Word-finding difficulty: a clinical analysis of the pro...

Word-finding difficulty: a clinical analysis of the progressive aphasias

The patient with word-finding difficulty presents a common and challenging clinical problem. The complaint of 'word-finding difficulty' covers a wide range of clinical phenomena and may signify any of a number of distinct pathophysiological processes. Although it occurs in a variety of clinical contexts, word-finding difficulty generally presents a diagnostic conundrum when it occurs as a leading or apparently isolated symptom, most often as the harbinger of degenerative disease: the progressive aphasias. Recent advances in the neurobiology of the focal, language-based dementias have transformed our understanding of these processes and the ways in which they breakdown in different diseases, but translation of this knowledge to the bedside is far from straightforward. Speech and language disturbances in the dementias present unique diagnostic and conceptual problems that are not fully captured by classical models derived from the study of vascular and other acute focal brain lesions. This has led to a reformulation of our understanding of how language is organized in the brain. In this review we seek to provide the clinical neurologist with a practical and theoretical bridge between the patient presenting with word-finding difficulty in the clinic and the evidence of the brain sciences. We delineate key illustrative speech and language syndromes in the degenerative dementias, compare these syndromes with the syndromes of acute brain damage, and indicate how the clinical syndromes relate to emerging neurolinguistic, neuroanatomical and neurobiological insights. We propose a conceptual framework for the analysis of word-finding difficulty, in order both better to define the patient's complaint and its differential diagnosis for the clinician and to identify unresolved issues as a stimulus to future work.

Key Words: aphasia; progressive aphasia; anomia; dementia; speech and language

Abbreviations: PPA, primary progressive aphasia; PNFA, progressive non-fluent aphasia; PSP, progressive supranuclear palsy; CBD, corticobasal degeneration; AD, Alzheimer's disease; AOS, apraxia of speech; DLB, dementia with Lewy bodies; FTD-MND, frontotemporal dementia associated with motor neuron disease; SD, semantic dementia; VaD, vascular dementia


Rohrer JD, Knight WD, Warren JE, Fox NC, Rossor MN, Warren JD. Word-finding difficulty: a clinical analysis of the progressive aphasias. Brain 2008 Jan;131(Pt 1):8-38.


INTRODUCTION

‘Word-finding difficulty’ is a common and challenging problem in neurological practice. In many cases, patients will complain of word-finding difficulty or, not uncommonly, the difficulty is identified by the neurologist in the course of the assessment. In both situations, the basis for the word-finding problem needs to be established but this is often not straightforward. Spoken communication depends on a sequence of cognitive processes, and disruption of any of these processes can affect word-finding (Fig. 1). Furthermore, processing occurs in a distributed network of brain areas that is vulnerable to a variety of acute and chronic pathological states (Levelt, 1989; Price et al., 1993; Levelt, 2001; Blank et al., 2002; Gorno-Tempini et al., 2004). The differential diagnosis of word-finding difficulty therefore encompasses a wide spectrum of acute and chronic disorders as diverse as delirium (Geschwind, 1964), aphasic stroke (Kertesz and McCabe, 1977), encephalitis (Okuda et al., 2001), major depression (Georgieff et al., 1998) and psychosis (Critchley, 1964), head injury (Levin et al., 1976), temporal lobectomy (Langfitt and Rausch, 1996) and metabolic and genetic disorders (Spinelli et al., 1995). In particular, however, it is a leading symptom of a number of degenerative conditions: the progressive aphasias (Mesulam, 1982, Hodges et al., 1992; Mesulam, 2003; Gorno-Tempini et al., 2004). In the degenerative diseases, in contrast to many of the other conditions associated with word-finding difficulty, the cause of the word-finding problem may not be obvious or it may be the presenting complaint: accurate diagnosis therefore depends on detailed characterization of the language deficit. It is accordingly in the context of degenerative disease that word-finding difficulty usually presents the greatest diagnostic challenge, yet the classical approach to the clinical assessment of language (which is based largely on the accumulated experience of aphasia in acute stroke: Hillis, 2007) may not be adequate. This reflects the often unique problems posed by speech and language breakdown in the degenerative dementias (Warrington, 1975; Mesulam, 2003).

___
Fig. 1 An outline of clinical syndromes and underlying functional deficits in patients with word-finding difficulty. Relations between acute and chronic syndromes and primary and secondary functional deficits are shown. Numerals refer to the operational stages in the language output pathway (dotted lines indicate processes that are related to but not essential for language output): I, generation of a verbal message; II, sense of the verbal message; III, structure of the verbal message; IV, motor programming of speech. Key: esp, especially; HSV, Herpes simplex encephalitis.
___

Here we use ‘word-finding difficulty’ as a shorthand for a class of symptoms which patients and carers commonly volunteer when describing impaired language output. Progressive cognitive syndromes with circumscribed deficits and preserved intellect have been recognized for many years (for example, Pick, 1892; Serieux, 1893, see also Luzzatti and Poeck, 1991; De Bleser, 2006 for other historical cases) and may preferentially affect a variety of cognitive domains, however the comparatively recent renaissance of interest in the language-based dementias (Mesulam, 1982) has transformed our picture both of disease biology in neurodegeneration and the organization of the human language system. The focal dementias pose considerable nosological and neurobiological difficulties. While circumscribed atrophy on structural brain imaging can support the impression of a focal dementia, diagnosis remains essentially clinical. Primary progressive aphasia (PPA) is a clinical syndrome of progressive language impairment with relative sparing of other aspects of cognitive function until late in the course (Mesulam, 1982, 2001, 2003). This broad definition subsumes substantial clinical, anatomical and pathological heterogeneity, and a spectrum of clinical subtypes of PPA has been described. While these subtypes have more or less distinctive profiles of speech and language disturbance, even where clinical characterization is robust (for example, in the distinction between ‘fluent’ and ‘non-fluent’ forms of PPA) understanding of the underlying pathophysiological mechanisms remains limited (Mesulam and Weintraub, 1992; Grossmann, 2002; Mesulam et al., 2003) Moreover, the overlap between clinical subtypes is substantial, incomplete syndromes are frequent (Grossmann, 2002; Mesulam et al., 2003), and none has been shown to have a unique correspondence with either anatomy or tissue pathology. This presents serious and unresolved nosological difficulties, and for the clinician, a substantial diagnostic dilemma. Furthermore, the stimulus of the focal language-based dementias has led to a wider appreciation of speech and language dysfunction in other neurodegenerative conditions, including Alzheimer's disease (AD) (Emery, 2000; Croot et al., 2000) and the problem of the differential diagnosis of ‘progressive aphasia’ in this broader sense. Accordingly, a conceptual framework is needed to allow the clinician to interpret the patient's complaint of word-finding difficulty in line with emerging evidence for language network dysfunction in neurodegenerative diseases.

Here we outline such a framework for the clinical analysis of ‘word-finding difficulty’. We propose a clinical scheme that can be used at the bedside to categorize the nature of the problem and to formulate a differential diagnosis, with reference in particular to the degenerative dementias, presented in Fig. 2. This scheme has speech as its focus because word-finding difficulty in spoken language is generally the dominant complaint in the progressive aphasias. Our scheme is informed by evidence emerging from the experimental brain sciences, and contemporary information-processing accounts of language processing (Levelt, 1989; Warren and Warrington, 2007; Hillis, 2007) (Fig. 1). Application of the scheme generates a taxonomy of clinical syndromes arising from different operational stages in the language output pathway and with distinct anatomical substrates. Our approach is based on a series of steps that probe the key stages in language output (Fig. 1). These steps are elaborated in the following sections and in Tables 1–4. The pattern of performance at each step identifies the cognitive processing stage that is principally affected and builds up a detailed profile of the speech syndrome. Both these levels of analysis are of clinical relevance: the broad cognitive operational level allows the deficit to be localized (Fig. 3), while the detailed syndromic description guides the differential diagnosis of the likely pathological process (Fig. 2). Our intention is to provide the neurologist with a bridge between the dilemmas of the bedside and the theoretical constructs of the brain sciences, rather than a comprehensive neurolinguistic treatise on the progressive aphasias. At the same time, however, we hope to show that understanding of the pathophysiology of these diseases can be advanced by the characterization of clinical phenomena that are difficult to reconcile with theoretical models of language function and dysfunction.

___
Fig. 2 A clinical scheme for assessing the patient with word-finding difficulty, particularly in the context of degenerative disease. The scheme is organized as a ‘grid’ in which each column represents a key step in the clinical assessment, and each row represents a speech or language syndrome. Each entry in the grid represents an abnormality. Based on the initial assessment of features of the patient's spontaneous speech directed toward key language operations (left; see also Fig. 1), followed by key speech and language tasks (centre), the clinical speech or language syndrome is characterized. Identification of the clinical syndrome allows a differential diagnosis to be formulated, based on associated clinical features (right) including both cognitive and other neurological abnormalities. These associated features also allow primary and secondary effects on word-finding to be interpreted (Fig. 1). See text for details. Key: filled circle: abnormal; AOS: apraxia of speech: *: as used in consensus criteria; {dagger}: nosological status not established; AD: Alzheimer's disease; bvFTLD: behavioural variant of frontotemporal lobar degeneration; CBD: corticobasal degeneration syndrome; CIRCUMLOC: empty, circumlocutory speech; COG: cognitive features; EPS: extrapyramidal syndrome; LTPS: lateral temporo-parietal syndrome; MND: motor neuron disease; PNFA: progressive nonfluent aphasia; PSP: progressive supranuclear palsy; SD: semantic dementia; SURFACE: surface (regularization) errors; VaD: vascular dementia.
___


___
Fig. 3 Structural anatomy of word-finding difficulty in degenerative disorders. Numerals and connecting arrows refer to the operational stages in the language output pathway (coded in Fig. 1 and Table 2). Key anatomical areas are indicated. Arrows are bi-directional to indicate that flow of information between these areas is likely to be reciprocal. Brain magnetic resonance images illustrate some degenerative disorders with word-finding difficulty (the left hemisphere is on the right side in all coronal sections; TL, temporal lobe): (a) asymmetric (left greater than right) frontal lobe atrophy, dynamic aphasia; (b) focal left anterior/inferior temporal lobe atrophy, semantic dementia; (c) bilateral mesial temporal atrophy, Alzheimer's disease (anomia); (d) left posterior superior temporal/inferior parietal atrophy, progressive ‘mixed’, logopenic or jargon aphasia; (e) focal left superior temporal lobe/insular atrophy, progressive nonfluent aphasia; (f) focal left inferior frontal gyrus/frontal opercular atrophy, progressive apraxia of speech.
___


___
Table 1 History of the problem

• What was the patient's previous level of verbal skill (bilingualism, formal education, occupation, specific learning difficulties, etc.)?
• How did the current problem begin, and how long ago?
• Since the onset is the problem unchanged, variable, deteriorating or improving?
• In what circumstances do word-finding problems typically occur (e.g. telephone conversations, public speaking, crossword puzzles, etc.)?
• Does the patient produce less speech overall than they used to? Do they initiate conversations less often?
• Can the patient communicate the idea of a message (despite pauses or errors), or is their meaning difficult to follow?
• Are the words used recognisable, are they pronounced correctly, and are they in context?
• Does the patient have difficulty understanding what is said to them or in following conversations or reading material?
• Is there a stutter (is this re-emergence of a childhood stutter)?
• Has the quality of the patient's voice altered (e.g. has it become softer or more monotonous)?
• Does the difficulty affect speech only, or is writing also affected?
• Are there other cognitive, behavioural or neurological problems?
___


___
Table 2 Analysis of spontaneous speech

I. Generating a message—verbal thought
• Does the patient find it difficult to initiate speech/conversation?
• Is the overall quantity of speech they produce diminished (or are they echolalic)?
II. The sense of the message—conceptual content and vocabulary
• Can the patient communicate the idea of a message (e.g. what is happening in the picture) or is the meaning of their spoken output difficult to follow (e.g. is the speech empty and/or circumlocutory)?
• Are there errors of meaning (semantic paraphasias)?
• Are there nonsense words (neologisms / jargon)?
• Are there stereotyped repetitive phrases?
III. The structure of the message—grammar and phonology
• Is speech ‘telegraphic’ (missing function words)?
• Are there other grammatical errors (use of wrong tense, words in the wrong order, incorrect use of plurals)?
• Are there speech sound errors affecting words and syllables (phonemic paraphasias)?
IV. Motor programming of speech—phonetics, articulation and prosody
• Is speech effortful?
• Is there a stutter?
• Are there distorted speech sounds (phonetic errors)?
• Are speech volume, rate, rhythm and intonation (prosody) normal?

See text and Tables 3 and 4 for examples; see Fig. 3 for anatomical localization.
___


___
Table 3 Examples of spontaneous speech in progressive versus acute aphasias (each of these patients is describing a beach scene, shown in Fig. 4)

Progressive aphasias:

Semantic dementia

That's the father, playing with his son, that thing (points to ball) ... hitting the thing in the air. (Pointing to boy falling out of boat) He's in the garden isn't he, playing that game again. I hope he doesn't fall down. Looks as if he's wobbling. (Pointing to sandcastle) I’m not quite sure. That's the water there, coming right up to there, and that stays there and he's working, he's pressing that down, isn't he? He's working it. He's moving it down there because that's the equivalent of that, and that goes there ... both sides. I’ve seen something like that somewhere else.

Alzheimer's disease (‘logopenic aphasia’)

A beach scene ... playing on the beach. A pier ... (pause) and a building on the pier and a row of beach (pause) things. (long pause) In the middle ground, a father and child playing with a large ball on the ... (pause). On the left.erm ... a rower has overbalanced next to the beach really ... and is falling out over the (pause) side of the erm. (pause) rowing boat. In the foreground is a youngster building some (pause) sandcastles.

Progressive nonfluent aphasia/apraxia of speech

The sea ... er ... er ... er ... um ... a man in a soup ... no suit ... with a panner (pointing at paddle) falling out of the boat. Er ... nice stand ... no sand next to the sea and the boy making a nice h. h. house ... houses. Another (long pause) m. m. m. man ... a big men ... no man ... and little g. g. g. girl p. p.p. playing. The two skygurls (points to seagulls). Water round castle ...


Acute aphasias

Broca's aphasia (left inferior frontal infarction)

It's picture of ... er ... ab ... about a ... a ... er. beach ... er ... holiday ... er ....er ... Father has gone down beach with his ... er ... (pause) three children ... erm ... He's playing with ... er ... a little ... maybe a ... er ... chil ... er ... girl or boy. He's having a ball and the ... the ... choldren. no ... the child is reaching for it.

Wernicke's aphasia (left temporo-parietal infarction)

A little boy with spanks an sparras. These are the ... It's got it on the high underground and a fly flow new boy, and the boy whose fallen in the water and the two children on the right there with one a bit two children. One childer and one in lyda and the child a boy in the flem of course. And that is the last one ... is the last one in the bottom.
___


___
Table 4 Specific speech and language tasks and the functions they assess (see text for examples)

Naming
- Lack of content words and proper nouns in spontaneous speech (see Tables 2 and 3)
- Naming of familiar items from pictures
- Naming from verbal description
- Effect of word frequency
- Effect of category (e.g. animate/inanimate; special cases, e.g. colours)
- Type of error (phonemic, speech sounds; semantic or neologistic, meaning)
- Effect of cueing (initial letter/semantic association)
Functions: retrieval of words from verbal knowledge store, verbal output

Speech comprehension
- Single words: vocabulary (point to items named by examiner, provide definitions, choose synonyms, categorise)
Functions: speech signal input, verbal knowledge storage
- Sentences: grammar (perform a short series of actions to command, identify a picture from description)
Functions: manipulation of on-line verbal information and grammatical relations

Speech repetition
- Monosyllabic words, polysyllabic words, phrases and sentences
Functions: speech signal input, verbal output, input:output transfer

Reading, writing and spelling
- Read a short passage aloud (including both irregular words and ‘nonsense’ words such as proper nouns)
- Write a sentence
- Spelling of regular and irregular words
Functions: verbal processing in other language channels
- Sentence generation and completion
- Sentence generation around a target word
- Sentence completion using terminal nouns (predictable versus open-ended)
Function: novel verbal thoughts and messages
- Motor assessment
- Repetition of single syllables
Function: articulation
- Repetition of syllable combinations
Function: phonetic encoding
___



THE CLINICAL BACKGROUND

The complaint of word-finding difficulty should not be taken at face value. The first task is to determine what is meant: defective speech output of various kinds may be described as a problem ‘finding words’, ‘finding’ (or ‘remembering’) names’, ‘getting words out’, ‘using the wrong words’, ‘jumbled’ or ‘mixed up’ words. Patients may complain that their vocabulary is reduced (particularly for more specialized material), there may be an inability to convey precise shades of meaning or loss of facility with crossword puzzles. Carers may have become aware of speech sound or grammatical errors in the patient's spoken or written output, or the appearance (or reappearance) of a stutter or alteration in voice quality. However, specific descriptions of this kind (though valuable) often must be actively elicited.

Although word-finding is central to normal communication, word-finding difficulty should not be equated with aphasia. Problems with word-finding may develop in the setting of otherwise normal language as a result of a problem in another cognitive domain. A major goal of clinical assessment, therefore, is to decide whether word-finding difficulty reflects a primary language disorder, or whether the problem is secondary to other non-linguistic cognitive deficits. Primary word-finding difficulty may occur as an isolated language disturbance or may occur as part of a more extensive cognitive or behavioural syndrome. Secondary word-finding difficulty occurs when a deficit within another cognitive domain interferes with the function of a more or less intact language system. For example, a patient in whom failure to name household objects on bedside testing is accompanied by a failure to locate or correctly use the same items may have a primary visual perceptual problem, patients who participate less in conversations may be deaf, while difficulty remembering the names of acquaintances or in delivering messages may indicate a more general problem with episodic memory. Conversely, patients with a primary word-finding difficulty and their carers often describe their symptoms in terms of memory failure (they may say that they ‘forget’ the names of people or things) or a perceptual defect (impaired speech comprehension is not uncommonly ascribed to ‘deafness’ by the patient's family). It is also important to recognize the wide spectrum of normal variation in word-finding ability, and the potential effects of fatigue, anxiety or mood disorders. The evaluation of word-finding ability therefore requires both an objective assessment of performance, and an awareness of the wider context in which the problem has developed and its impact on the patient's daily life.

Obtaining an accurate history of word-finding difficulty (Table 1) depends on interviewing both the patient and an informant who knows the patient well. A complaint of word-finding difficulty must be interpreted in light of a patient's premorbid verbal skills. Information about bilingualism (was English the first language, and if not, what level of competence was achieved?), educational attainment and literacy, occupation and any premorbid disabilities (such as developmental dyslexia) is essential. The family history may be relevant not only to the diagnosis in general but also to the interpretation of the word-finding problem in particular: an example is the emerging association of mutations in the progranulin gene with familial forms of progressive non-fluent aphasia (PNFA) (Cruts et al., 2006; Mesulam et al., 2007). Establishing the mode of onset and time course of the word-finding difficulty will assist in distinguishing acute processes (for example, stroke, encephalitis, delirium), chronic processes with static or fluctuating deficits (for example, head-injury or seizures) and chronic processes with progressive deficits (for example, a degenerative dementia). This information is particularly critical where the process leading to language breakdown has developed insidiously and there may be few other clinical clues to aetiology [for example, the interictal ‘pseudodementia’ of temporal lobe epilepsy: (Mayeux et al., 1980)]. The context in which the problem developed may be crucial. Whereas in acute disease processes, associated disturbances of alertness, perceptual and motor functions are often prominent (or may dominate the clinical presentation); in chronic disease processes, associated features may be subtle. However, the distinction between acute and chronic processes is not always clear. Patients who have sustained an acute event may present later with ongoing word-finding difficulty: accurate diagnosis then depends on establishing the degree of initial recovery and whether the word-finding deficit has evolved over time. Conversely, neurodegenerative disease can occasionally appear to present acutely following a particular event e.g. surgery (Larner, 2005). This may be secondary to a superimposed acute confusional state or due to the fact that mild word-finding or cognitive difficulties had previously gone unnoticed: the key to diagnosis here is to establish a background of more insidious or progressive difficulty prior to the acute presentation. The history often provides clues to the nature of the word-finding difficulty and associated cognitive, behavioural or neurological features which can then be explored systematically during the examination.


ANALYSIS OF SPONTANEOUS SPEECH

Systematic analysis of an extended sample of the patient's spontaneous (propositional) speech (Table 2) is the single most valuable aspect of the examination. Where little spontaneous conversation is offered, the patient can be asked to describe a scene in a photograph or drawing (an example is shown in Fig. 4A). This is preferable to asking the patient to recount an event in their daily routine, as it allows speech to be evaluated independently of episodic memory and provides a standard with which to compare speech characteristics in different clinical situations. Examples of scene descriptions produced by patients with canonical speech disorders are presented in Table 3. Valuable information is often obtained from observing the patient's general behaviour and approach to the clinical interview. The inert patient with a frontal dementia, who offers little speech at all and sits passively throughout the interview, makes a very different impression from the patient with PNFA, who is obviously frustrated by their difficulties and struggles to compensate with an excess of non-verbal gestures, and both contrast with the garrulous patient with semantic dementia (SD), who produces a steady stream of circumlocutory speech.

___
Fig. 4 Materials for assessing speech at the bedside. (Reproduced with permission of Professor EK Warrington.) (A) A beach scene, illustrating one means of eliciting conversational speech (see examples in Table 3). (B) A passage for reading aloud (see text).
___


The classification of aphasias as ‘expressive’ or ‘receptive’ (or ‘motor’ or ‘sensory’) is both overly simplistic and inaccurate (Geschwind, 1971): few patients present with either a pure speech production or comprehension deficit. This is true for acute lesions (Brust et al., 1976), but particularly relevant to the categorization of the progressive aphasias. Similarly, classifying speech disturbances as ‘fluent’ or ‘non-fluent’ also oversimplifies the clinical phenomenology and is open to misinterpretation. Fluency describes the flow of speech output, but it is multidimensional: ‘non-fluency’ may be due to a number of different factors, including decreased phrase length, agrammatism, poor articulation or slower speech rate (Hillis, 2007). As these impairments tend to occur together, an individual patient's speech can often be reliably categorized as fluent or non-fluent; moreover, certain dimensions (particular motor aspects such as rate and articulation) make a relatively greater contribution to the impression of dysfluency. However, the component processes are dissociable: thus, patients with milder forms of ‘non-fluent’ speech may still produce relatively long phrases or sentences, albeit containing many errors. Even in more advanced cases of ‘non-fluent’ speech, there may be stereotyped phrases comprising several words (e.g. ‘Hello, how are you?’): such phrases can be regarded as an expressive ‘unit’ serving a similar function to a single word. Conversely, patients with ‘fluent’ aphasias generally have empty speech due to an impaired ability to find appropriate content words but commonly also have conversational pauses during which they struggle to find the appropriate word: these gaps tend to reduce the overall number of words produced (‘logopenia’) and thus the fluency of the utterance as a whole. Although it remains clinically useful as a descriptive term, ‘fluency’ is therefore potentially misleading as a criterion for the categorization of speech and language syndromes, which is more usefully based on a combination of features (Fig. 2).

All propositional speech can be considered as an attempt to convey a thought or ‘message’ in verbal form, and the operational stages involved in this process (Fig. 1) suggest a broad classification of clinical deficits, according to whether the patient has difficulty initiating conversation, difficulty in conveying the sense of the message (a disturbance of speech content such that thought can no longer be conveyed coherently) or with message structure (a disturbance of word formation or word order). In practice, an individual patient's word-finding difficulty is rarely confined to a single one of these categories, although in many cases one category will predominate. Furthermore, deficits in these true word-finding categories may overlap with a difficulty in the motor programming of speech: production of intelligible words ultimately depends on an intact motor programme that enables correct articulation of a formulated utterance.

Generating a message: verbal thought

The ease of initiation of conversational (propositional) speech provides important information about the generation of verbal thought (the ability to express thoughts in words). This process involves the formulation of a plan for the verbal message (Fig. 1). Although patients with word-finding difficulty of all kinds may participate less in conversations as a non-specific result of reduced facility with language, a striking reduction in propositional speech is the hallmark of dynamic aphasia (Luria and Tsvetkova, 1967; Costello and Warrington, 1989; Robinson et al., 1998; Warren et al., 2003). The patient seems literally to have ‘nothing to say’. Such patients have a selective deficit at the level of the generation of verbal thought: although the amount of speech is reduced, the sense and structure of the message (provided it can be generated in the first place) usually remain intact. Sentence generation is dependent on context: a patient may be able to describe a simple picture but may not be able to talk to an everyday topic or may provide a sparse (but error-free) description of a complex scene (Fig. 4A). Compared to this decreased spontaneous output, speech can be produced relatively normally in specific contexts, such as naming tasks, repetition or reading. A similar decrease in speech output occurs in many patients with frontal and subcortical deficits who exhibit a generalized inertia and slowing of thought. However in pure dynamic aphasia there is retained ability to generate novel non-verbal material such as song, suggesting that dynamic aphasia is a true language disorder and not simply a consequence of abulia (Warren et al., 2003).

Some patients with impaired generation of verbal messages have defective (rather than simply absent) verbal output. The occurrence of spontaneous verbal stereotypies or echolalia (repetition of others’ utterances) suggests a loss of capacity for self-generated verbal thought; such phenomena are often associated with other evidence of environmental dependency in patients with frontal lobe or fronto-subcortical damage (Denny-Brown, 1956; Bathgate et al., 2001).

The sense of the message: conceptual content and vocabulary

Once a plan for a verbal message is generated, the message must be elaborated with specific content and function words. The sense of a spoken thought or message depends on its conceptual content. It is possible to convey the constituent concepts of a message even where the structure is disorganized or degraded, and the converse is also true. To take the example of the message ‘the bird sat on the branch’: compare ‘bird sat branch or ‘the birt sit on the brench’ (content preserved, structure degraded) with ‘the thing pit on the tam’ (structure preserved, content degraded). The content of speech can be assessed at the level of individual words themselves, and the way they are combined to convey a more extended message in a sentence (Fig. 1).

Impaired content at the level of individual words is evident as a deficient vocabulary—the patient may use approximate or imprecise expressions (circumlocutions) that substitute for a single word (e.g. ‘the thing’, ‘the whatchamacallit’) and speech (though fluent) may seem vague and lacking in substance. Errors of meaning or ‘semantic paraphasias’ may be evident as context-inappropriate words (for example, ‘dog’ may be used when ‘pig’ is meant). Superordinate or generic terms (such as ‘animal’) are used rather than more specific ones (such as ‘squirrel’ or ‘lobster’) and often accompany the use of circumlocutory phrases in an attempt to compensate for the deficiency of vocabulary. There may also be increased reliance on stereotyped expressions, stock phrases and clichés. Such fluent but ultimately empty speech is characteristic of conditions in which there is damage to the verbal knowledge store, the paradigm for which is SD with focal degeneration of the left temporal lobe (Warrington, 1975, Snowden et al., 1989; Hodges et al., 1992; Chan et al., 2001). In this situation there is often evidence from the history and on further specific language tasks for impaired comprehension of single-word meaning. A more common scenario is difficulty retrieving words from storage despite evidence that comprehension of the meaning of words (at least initially) is well preserved: this situation prevails in a range of different disorders, including early AD, and indeed can be considered ‘word-finding difficulty’ in its purest operational sense. In this situation there may be prolonged word-finding pauses affecting both spontaneous discourse and naming. Linguistic deficits arise at an early stage in ~10% of cases of typical amnestic AD: impaired verbal fluency is typically prominent (Emery, 2000), whereas speech production is characteristically relatively preserved in the earlier stages of the disease (Bayles and Kasniak, 1987). In some patients with progressive aphasias, idiosyncratic or novel expressions (neologisms) may dominate speech output, ‘jargon aphasia’ (Marshall, 2006): this is rare in degenerative disease (Ostberg et al., 2001; Rohrer et al., 2007).

Impairments of sentence-level content manifest as a lack of coherence in conveying the message—sentences may trail off unfinished, or tangential and context-inappropriate words or fragmentary phrases may be inserted, so that it is difficult to follow the patient's line of thought. Disordered speech of this kind is observed in acute brain syndromes, in which attentional and executive deficits may make organized or sustained verbal expression impossible (Chedru and Geschwind, 1972), and also in the intermediate and later stages of AD. Disorganized verbal output at the level of more complex narrative or discourse is a feature of the behavioural variant of frontotemporal lobar degeneration (bvFTLD), in which executive dysfunction is typically prominent (Ash et al., 2006). Though not conventionally considered with the canonical language syndromes, such higher-level difficulties with verbal output illustrate the wide range of phenomena that may impair patients’ ability to communicate and the limitations of conventional models of ‘aphasia’.

The structure of the message: grammar and phonology

The structure of a verbal message can be considered at two levels: grammar, the ordering of words at the level of phrases and sentences, including the use of ‘function words’ (articles, prepositions and conjunctions); and phonology, the selection and ordering of individual sounds into syllables and words. Impaired grammatical structure (agrammatism) typically manifests as disjointed or ‘telegraphic’ speech composed of single words and short phrases, omitting function and connecting words (e.g. ‘bird sat branch’). Incorrect ordering of words may occur, grammatical elements such as plurals or tenses may be misused or binary grammatical alternatives (such as ‘yes – no’, ‘him – her’) may be confused (Frattali et al., 2003). Impaired phonological structure manifests as speech sound errors, or ‘phonemic (‘literal’) paraphasias’ at the level of individual words and syllables, most commonly substitutions (‘crabon’ for ‘crayon’), transpositions (‘aminal’ for ‘animal’), omissions (‘elphant’ for ‘elephant’) or additions (‘hippopototamus’ for ‘hippopotamus’) (Duffy, 2005). Such errors often first appear and remain more evident with polysyllabic words. Agrammatism and phonemic errors are typical features of PNFA (Neary et al., 1998, Gorno-Tempini et al., 2004; Grossman and Ash, 2004) and help distinguish this syndrome from the language output difficulties observed in patients with AD (Mendez et al., 2003) (Table 3). Agrammatism and phonological breakdown commonly occur together but relatively pure dissociations have been described in degenerative disease (Caramazza et al., 2000). Agrammatism may be partly masked by other speech-production impairments, unless more detailed testing of the receptive aspects of sentence comprehension or written output is undertaken (Bak et al., 2001, 2006; Code et al., 2006).

Motor programming of speech: phonetics, articulation and prosody

Disorders of the motor programming of speech (Fig. 1) have a different clinical significance from true word-finding difficulty. Nevertheless such deficits frequently co-occur, and this assists in anatomical localization and diagnosis. Here we consider these deficits at some length, because they are difficult to characterize with precision and because they entail several concepts which continue to stimulate controversy in the literature on progressive aphasias. One example is apraxia of speech (AOS). This term has been used to describe a motor speech disorder which (by analogy with other ‘apraxias’) can be defined operationally as impairment of the motor gestures of speech that is not attributable to a primary motor deficit (Darley, 1969; Ogar et al., 2005). Although the cognitive basis of AOS remains controversial, it is likely to arise at the level of cortical programming of phonetics, the step in speech production where the phonological structure is converted into an ‘articulatory score’ that directs the relevant muscles of the vocal tract to produce the word or phrase. AOS is probably therefore synonymous with phonetic breakdown or disintegration. The characteristic features of AOS are slow speech rate with hesitancy (difficulty initiating utterances), effortfulness (with articulatory groping, i.e. multiple attempts at trying to get to the right word and self-correction, worse with longer words), phonetic errors (errors in the shaping, timing and ordering of individual syllables) and dysprosody (abnormal rhythm, stress and intonation, attributable to poor phonetic sequencing rather than a primary prosodic deficit) (Dabul, 2000; Duffy, 2005; Ogar et al., 2005; Duffy, 2006). Patients may describe the problem as a stutter or stammer and there may be re-emergence of a childhood stutter. In a recent review of AOS in degenerative disease, only 10% of cases occurred in an isolated fashion, independently of aphasia or dysarthria (Duffy, 2006). It is associated particularly with PNFA (Josephs et al., 2006a; Duffy, 2006).

In principle, phonetic errors (errors in the execution of a programmed speech sound) are distinct from phonemic errors (errors in the selection of speech sounds to be executed): speech sounds may be selected correctly during the programming of an utterance but then articulated incorrectly or conversely, speech sounds may be selected incorrectly but then articulated correctly. However, in practice this is a difficult distinction to make at the bedside, and the two types of error frequently coexist. Clues to phonetic errors include the presence of distortions (commonly either distorted substitutions e.g. ‘brop-er-ty’ for the target word ‘property’, or additions e.g. prop-er-ta-ty’) and the co-occurrence of other features of AOS. This is in contrast to patients with pure phonological or phonemic breakdown: true phonemic errors are not distorted and speech is not effortful (Caramazza et al., 2000).

Speech features such as volume, rate, rhythm and intonation relate principally to the motor programming of speech output. These non-verbal aspects of speech output are most commonly affected in extrapyramidal disease [for example, the disorder of speech timing in Huntington's disease (Darvesh and Freedman, 1996)], and with cerebellar and subcortical (pseudobulbar or bulbar) pathologies. Such speech disturbances are often subsumed under the term ‘dysarthria’. Although dysarthria is most commonly secondary to a ‘peripheral’ disorder, it can occasionally be produced by cortical damage (progressive ‘cortical’ dysarthria or anarthria) (Broussolle et al., 1996; Silveri et al., 2003a; Soliveri et al., 2003). Dysarthric patients are likely to complain of slurred speech (or rarely, an altered or ‘foreign’ accent: e.g. Luzzi et al., 2007), reduced voice volume or other motor symptoms. Dysarthric and phonetic speech errors are generally difficult to distinguish. However, patients with phonetic impairment (AOS) make variable, inconsistent sound errors, and may articulate a word correctly on one occasion but not another, whereas the patient with dysarthria tends to make consistent errors. Like progressive AOS, isolated progressive dysarthria is rare and also overlaps with PNFA. Indeed, it is likely that all three disorders have frequently been conflated in the literature (Duffy, 2006), due both to the overlap and difficulty in distinguishing them and still unresolved problems of definition. This is underlined by the plethora of terms for motor speech disorders in the literature: ‘pure progressive aphemia’ (Cohen et al., 1993), ‘primary progressive anarthria’ (Silveri et al., 2003a), ‘slowly progressive anarthria’ or ‘anterior opercular syndrome’ (Foix–Chavany–Marie syndrome) (Broussolle et al., 1996).

Patients with progressive AOS or cortical dysarthria classically have well-preserved writing, indicating that these are disorders of speech output and that language processing per se is spared (Broussolle et al., 1996; Silveri et al., 2003a). In contrast, impairment at the level of phonological structure will manifest as phonemic errors in both speech and writing. Comparison of the patient's speech and writing is therefore generally a useful means of distinguishing primary phonological and phonetic disorders at the bedside. The severity of the speech deficit also provides a clue: patients with impaired motor programming of speech often have profoundly impaired speech production eventually leading to mutism. However, mutism is an end-stage of a number of disease processes (Kertesz and Orange, 2000) and can occur as an early feature in PNFA (Gorno-Tempini et al., 2006).

Other components of the motor programme that are functionally separate from phonetic encoding can also be disrupted by degenerative disease: a key example is prosody, the intonational pattern of pitch, stress and timing that constitutes the ‘melody’ of speech (Ross, 1981). Many patients with speech-production difficulties lose the normal rhythms of conversational speech and the ability to regulate fine pitch and accent shifts. If severe, dysprosody may disrupt the intelligibility of the utterance as a whole and could be misinterpreted as a primary verbal problem. Commonly, dysprosody is secondary to poor articulation but rare cases of primary progressive dysprosodia have been described (Confavreux et al., 1992; Ghacibeh and Heilman, 2003).


SPECIFIC SPEECH AND LANGUAGE TASKS

The patient's word-finding difficulty can be further analysed using specific speech and language tasks (Table 4), which both corroborate the information obtained so far and may also expose additional deficits. As a result of these tasks, it should be possible to categorize the word-finding difficulty in terms of a core defect (summarized in Fig. 1), leading to a more detailed characterization of the speech or language syndrome (Fig. 2). Each of the suggested bedside tasks can be refined and amplified by more specialized and detailed neuropsychological tests. These allow the language disorder to be quantified or characterized in more detail than is usually possible at the bedside and may allow the identification of mild or ‘subclinical’ deficits that more fully define the cognitive phenotype. This is particularly useful in detecting and tracking disease progression. The information obtained at neuropsychometry, however, is most useful if the neuropsychologist is guided by information provided by the neurologist based on an initial bedside characterization of the problem and differential diagnosis.

Naming

Word-finding depends fundamentally on a capacity to retrieve words from the verbal knowledge store in the appropriate context. This is most conveniently assessed as the ability to name. However, this ability is not related simply to word retrieval: it is an active and multi-step process (Grossman et al., 2004) which calls upon many of the cognitive operations outlined in Fig. 1. Impaired naming, or anomia, is frequent in patients who complain of word-finding difficulties (indeed, patients and their carers frequently characterize the language deficit as a problem with names), and it is a feature of many different disorders. The diversity of clinical situations that lead to anomia underlines the need to evaluate other cognitive functions in order to arrive at a diagnosis. Although pure anomia is uncommon in degenerative settings, both primary verbal storage and word retrieval disorders typically present with anomia. Anomia is the most salient linguistic feature of early AD (Mendez et al., 2003; Blair et al., 2007): in this context, the diagnosis is usually based on impairments in other cognitive domains (notably, episodic memory; see next section). Early striking anomia is a characteristic feature of SD: in this situation, more sophisticated neuropsychological instruments may be required to expose the primary semantic defect (see for example, Howard and Patterson, 1992; Warrington et al., 1998). Because of its importance as a presenting symptom, the broad spectrum of clinical associations and the fundamental role of word retrieval in the language output pathway, we consider the problem of anomia and its practical evaluation in detail.

The evaluation of naming begins with the analysis of the patient's spontaneous speech (see previous section and Tables 2 and 3). Clues to anomia include a dearth of content words (especially low frequency or proper nouns), abundant circumlocutions or frequent word-finding pauses. The nature of the defect is established using a structured series of subtests designed to assess different aspects of naming. Poor performance on these naming tasks may lead to the characterization of a word-finding problem even in patients who do not present with a primary complaint of word-finding difficulty. Conversely, particular patterns of performance on naming tasks may help to establish that the basis for the word-finding impairment lies beyond (or is not confined to) the language system. Naming of objects in the environment depends on intact perceptual processing and activation of the appropriate semantic associations by the percept; only if these operations are successfully accomplished can verbal processing proceed.

Naming should be tested directly both in response to pictured items (confrontational naming) and from verbal description (e.g. ‘a large grey animal with a trunk’). Primary deficits of visual perception or visual knowledge manifest as a better performance in naming to verbal description than naming pictures. Having established a primary verbal deficit, naming performance should be assessed for words of both high and low frequency (e.g. ‘shoe’ versus ‘moat’) as subtle deficits may not emerge for confrontational naming of highly familiar items (Warrington, 1975). It should be established whether there is improvement with phonological (first letter) or semantic (associated item) cueing. Different categories of items should be presented (animals, inanimate objects, familiar faces, colours, nouns versus actions, etc.). Striking category effects are more commonly observed in acute brain damage (such as herpes simplex encephalitis) than in degenerative disease (Warrington and Shallice, 1984; Silveri et al., 1991; Laws et al., 2003), however selective deficits or sparing of noun categories have been described in SD (Robinson and Cipolotti, 2001; Incisa della Rochetta and Cipolotti, 2004; Zannino et al., 2006) and AD (Garrard et al., 1998). Naming deficits may be relatively specific for a particular grammatical class (for example, naming of verbs may be more impaired than naming of nouns in PNFA (Hillis et al., 2002), or selectively spared in AD (Robinson et al., 1999): it is debatable whether this is a primary verbal defect or part of a broader deficit involving knowledge of actions versus objects (Bak et al., 2006).

Naming errors
Any errors made on naming tasks should be recorded: the type of naming error provides important information about the primary defect. Deficits of visual perception manifest as ‘visual’ errors on confrontational naming tasks (for example, a line drawing of a teapot may be called a face). With primary involvement of the verbal knowledge store, there are typically highly consistent deficits that affect naming both to confrontation and from description, but which affect unusual (low frequency) items (e.g. hippopotamus) more than common (high frequency) items (e.g. cat). Naming errors take the form of semantic paraphasias: incorrect semantic categorisations (which may be from related categories: for example, a camel may be called a horse), or substitution of a generic category for a more specific one (for example, a hippopotamus and a lobster may both be called animals, or all animals may become ‘dog’). There may also be circumlocutory responses (e.g. a picture of a squirrel may elicit ‘they live in the garden, grey in colour’). Such errors are characteristically made by patients with SD, however similar errors are also observed not uncommonly in other dementias, including AD and vascular dementia (VaD) (Lukatela et al., 1998) and should be interpreted cautiously.

Deficits involving the process of word retrieval proper (common in early AD) lead to a relatively pure anomia: in this situation, knowledge about words and the phonological encoding of words are preserved, but the means for accessing these stores or linking stored word information with the appropriate phonological code is defective (Hillis, 2007). The selective nature of the anomia can be established from the overall pattern of performance on naming versus other speech and language tasks. On confrontational naming tasks, such patients may offer no response at all or they may produce circumlocutions or semantically (or phonologically) related alternatives to the target item, either due to aberrant activation of alternative stored word codes or in an attempt to compensate for their naming difficulty. Although the nature of circumlocutions and semantic paraphasias in nominal aphasia has been recognized for many years (Luria, 1970), these are frequently misinterpreted as evidence for a primary semantic (verbal knowledge store) defect. Clues to the true nature of the deficit are a tendency to hunt spontaneously through related items in the semantic field (‘it's not a fox ... not a rat ... it eats nuts ... it's a squirrel’) or for naming performance to improve when such additional semantic associations are provided, and retained ability to recognize the correct name when alternatives are presented by the examiner. More conclusively, single word comprehension is intact (see later), whereas this is impaired from an early stage of the illness in diseases (particularly SD) with primary verbal semantic impairment.

Naming errors in patients with a primary breakdown in the phonological encoding of verbal concepts into speech sounds (as in PNFA) generally take the form of literal (phonemic) paraphasias (e.g. ‘hotapitamus’ for hippopotamus) that approximate the target item and which are usually also evident in other contexts (for example, speech repetition) (Mendez et al., 2003). Primary deficits of both word retrieval and phonological encoding (in contrast to primary verbal store defects) may benefit from cueing with the initial letter of the target word. Indeed, patients may complain that the words that elude them in conversation are ‘at the tip of the tongue’ (Delazer et al., 2003; Hillis, 2007). Personal names may present particular difficulties: this is likely to reflect the combined demands of accessing stored information about the subject's identity, retrieving that information from storage, and encoding it phonologically (since proper nouns are generally ‘non-words’ rather than part of the universal lexicon) (Delazer et al., 2003), though the rare occurrence of selectively spared proper names does raise the possibility of separable brain stores (De Bleser, 2006). Neologisms on confrontational naming tasks are comparatively rare in degenerative disease, however the presence of jargon should be noted as it may be of localising value (Fig. 3).

Speech comprehension

Speech-comprehension difficulties commonly coexist with word-finding and language output problems in both acute settings (such as left hemisphere stroke) and degenerative disease. Speech comprehension can be assessed at the level of single words, which depends both on intact perceptual mechanisms and the verbal knowledge store (vocabulary), and sentences, which depends on the ability to hold verbal information on line and to process grammatical relations between words.

Single-word comprehension
Impaired single-word perception manifesting as progressive word deafness has been described rarely in degenerative disease (Serieux, 1893; Mesulam, 1982; Ikeda et al., 1996; Otsuki et al., 1998): these patients have difficulty both in understanding and repeating spoken words but normal comprehension of written material, and speech output is often loud and dysprosodic and may contain phonemic substitutions. The perceptual deficit is likely to lie with auditory temporal acuity and discrimination of speech sounds (Otsuki et al., 1998) and often leads to associated impairments of environmental sound and/or music perception (Serieux, 1893; Otsuki et al., 1998): an apperceptive auditory agnosia. The auditory deficit can be demonstrated at the bedside by testing discrimination of phoneme pairs (e.g. ‘pat – tap, ‘gat - cat’).

Impaired comprehension of single words in the setting of intact acoustic analysis results from a breakdown in verbal knowledge systems. The most striking and selective deficits of single-word comprehension are associated with SD, however semantic impairment is also well documented in AD (Hodges et al., 1993; Garrard et al., 1998, 2005). Primary deficits of the verbal knowledge store lead to reduced vocabulary and also impair comprehension of both spoken and written material at single-word level. The comprehension of nouns can be assessed by asking the patient to point to items named or otherwise described by the examiner, to generate a definition or provide other information about a target word (e.g. ‘What is a squirrel?’), or to choose between alternative synonyms for a target word (e.g. does ‘trench’ mean ‘hedge’ or ‘ditch’?). This can be finessed according to the examiner's assessment of the patient's premorbid level of competence (for example, a highly competent patient with excellent premorbid verbal skills could be asked the difference between laziness and idleness). Defects of word knowledge can be further probed by asking the patient to classify items according to nominated criteria (for example, ‘Is a lion a mammal?’). Degradation of word knowledge typically progresses from more specific to superordinate categories (for example, loss of knowledge about dogs might evolve in the sequence: dachshund—dog—animal). Typically, meaning is retained for broad categories of nouns when more fine-grained classifications are impossible. It is important to take account of this when interpreting patients’ responses, and to be prepared to probe for more detail than the patient may initially volunteer: asked ‘what is a hippo?’, the response ‘it's an animal’ indicates only a very general level of superordinate knowledge; one would expect to be able to elicit further information (‘big, lives in Africa, in the water’) if the verbal knowledge store is intact. Comprehension of verbs can also be assessed, for example by having the patient select an appropriate description of actions pantomimed by the examiner (‘pushing’ versus ‘pulling’, ‘catching’ versus ‘throwing’, etc.) or by asking them to produce actions nominated by the examiner. In patients with very impaired language output (for example, in the context of PNFA), gestures can also be used as a tool to assess comprehension of single words (nouns), provided readily manipulable items are chosen (for example, ‘shovel’ or ‘teapot’) and there is not an associated dyspraxia or significant motor deficit.

The organization of brain knowledge systems, in particular the extent to which different modalities and categories of knowledge are dissociable, remains a core theoretical issue in contemporary cognitive neuropsychology. Category-specific deficits of verbal knowledge have been documented in degenerative disease, but category effects are unusual and occur much less frequently than with acute pathologies. There may be selective impairment of the ability to comprehend the names of living things (McCarthy and Warrington, 1988; Lambon Ralph et al., 2003) or inanimate items (Silveri et al., 1997), or concrete versus abstract words (Warrington, 1975). Conversely, there may be relatively preserved comprehension of the names of body parts (Coslett et al., 2002), colours (Robinson and Cipolotti, 2001) or countries (Incisa della Rochetta et al., 1998). Though rare, category-specific deficits are of theoretical importance: the existence of such category effects, together with the consistency of deficits observed in SD and evidence for retention of partial knowledge in SD and AD (Murre et al., 2001; Garrard et al., 2005), argues for degradation of stored concepts (i.e. direct involvement of the knowledge store) rather than loss of access to the knowledge store. One well-established category effect in degenerative disease is the dissociation between noun and verb knowledge. Impairments of noun retrieval and comprehension are well documented (Silveri et al., 2003b) and usually are most salient in SD. Conversely, selective impairments of verb retrieval and comprehension have been demonstrated in patients with frontal dementia syndromes including frontotemporal dementia associated with motor neuron disease (FTD-MND) (Bak et al., 2001). Such patients have particular difficulty in processing verb phrases, and may rely more heavily on noun phrases (such as ‘laddering’ for ‘climbing’) and ‘superordinate’ verbs (such as ‘being’, ‘making’ or ‘having’).

Sentence comprehension
Under most circumstances in daily life, words must be processed not in isolation but combined into sentences. Difficulty with sentence comprehension may occur despite normal single-word comprehension. This pattern suggests that the processing of grammatical relations is deficient, and it may also be associated with particular difficulty understanding verbs rather than nouns (Price and Grossman, 2005). Having established that the comprehension of single words (nouns) is normal, the sentence level of comprehension can be assessed by asking the patient to perform a short sequence of actions according to different syntactic rules (e.g. ‘put the paper underneath the pen that is on the book’, ‘you pick up the watch and then give me the book’). Alternatively, the patient can be asked to identify a picture based on a syntactical sentence description (e.g. ‘point to the boy being chased by the dog’). The comprehension of grammar involves a number of different procedures (including determination of tense and number, interpretation of pronouns and prepositions, analysis of word order and subject-object relations and parsing of clauses). These procedures can be broadly classified as syntactical (relations between words) and morphological (word modifications according to grammatical context) and may have distinct neural bases. Some aspects of grammar processing may be dissociable from sentence comprehension (Cotelli et al., 2007) and can be assessed by asking the patient to detect grammatical errors within written sentences.

Patients with progressive aphasias may exhibit different types of deficits on sentence comprehension tasks, and these may assist in differential diagnosis. An early selective deficit in comprehending grammatical relations may be found in PNFA (Grossman, 2002; Grossman and Moore, 2005; Price and Grossman, 2005), whereas in SD, comprehension of syntactical constructions is typically intact within the limitations of reduced vocabulary. More subtle impairment of sentence comprehension has been documented in patients with AD: this is likely to be multifactorial in origin, including deficits in comprehension of pronouns (Almor et al., 1999) and in processing the structural and semantic coherence of sentences (Grossman and Rhee, 2001; Price and Grossman, 2005). However, other elements of grammar (such as gender, person and tense inflections) may be comprehended normally (Kavé and Levy, 2003). Sentence comprehension impairments have been documented in patients with bvFTLD not conventionally considered ‘aphasic’ (Cooke et al., 2003): in such patients, executive dysfunction and impaired working memory for complex syntactic constructions are likely to be responsible, emphasising the multidimensional nature of sentence comprehension and its susceptibility to a variety of different disease processes.

Speech repetition

Repetition of heard speech depends on intact input and output pathways and the ability to transfer information between these pathways. Accordingly, difficulties with speech repetition occur in patients with impaired processing of incoming speech signals (such as word deafness) and in those with impaired speech output. Like speech comprehension, repetition can be assessed at the level of words and sentences. Patients with word deafness or primary speech production problems may have difficulties even with single word repetition (especially for polysyllabic words) (Westbury and Bub, 1997). Repetition is hesitant and effortful and there are typically many phonemic errors. Patients with agrammatism may show a selective deficit in the repetition of phrases, particularly if these contain novel word combinations (clichés may be repeated more successfully, probably because they are processed as a single unit rather than a string of separate words). Single-word repetition is generally preserved in SD, though sentence repetition is influenced by the level of comprehension. Where comprehension of individual words is lost, there may be ‘migration’ of phonemes between words (e.g. ‘the flag was co