Normal Pressure Hydrocephalus - Normal Pressure Hydroce...

Normal Pressure Hydrocephalus

Normal Pressure Hydrocephalus

Arif Dalvi, MD, Assistant Professor, Department of Neurology, University of Chicago, Co-director of Parkinson's Disease and Movement Disorders Center

Updated: Apr 9, 2007

INTRODUCTION


Background

Normal pressure hydrocephalus (NPH) is a clinical symptom complex characterized by abnormal gait, urinary incontinence, and dementia. It is an important clinical diagnosis because it is a potentially reversible cause of dementia. First described by Hakim in 1965, NPH describes hydrocephalus in the absence of papilledema and with normal cerebrospinal fluid (CSF) opening pressure on lumbar puncture.


Pathophysiology

NPH differs from other causes of adult hydrocephalus. An increased subarachnoid space volume does not accompany increased ventricular volume. Clinical symptoms result from distortion of the central portion of the corona radiata by the distended ventricles. This includes the sacral motor fibers that innervate the legs and the bladder, thus explaining the abnormal gait and incontinence. Dementia results from distortion of the periventricular limbic system.

The term "normal pressure" hydrocephalus was based on the finding that all 3 patients reported by Hakim and Adams showed low CSF pressures at lumbar puncture, namely 150, 180, and 160 mm H2 O. However, an isolated CSF pressure measurement by lumbar puncture clearly yields a poor estimation of the real intracranial pressure (ICP) in patients with NPH.

Hakim first described the mechanism by which a normal or high-normal CSF pressure exerts its effects. Using the equation, Force = Pressure X Area, increased CSF pressure over an enlarged ependymal surface applies considerably more force against the brain than the same pressure in normal-sized ventricles. Normal pressure hydrocephalus may begin with a transient high-pressure hydrocephalus with subsequent ventricular enlargement. With further enlargement of the ventricles, CSF pressure returns to normal; thus the term NPH, at least in view of the initial pathophysiologic events, is a misnomer. Intermittent intracranial hypertension has been noted in some patients.

Some authors prefer the term extraventricular obstructive hydrocephalus. They believe that the initial event is diminished CSF absorption at the arachnoid villi. This obstruction to CSF flow leads to transient high-pressure hydrocephalus with subsequent ventricular enlargement. As the ventricles enlarge, CSF pressure returns to normal.


Sex

No gender proclivity is demonstrated with NPH.


Age

NPH occurs in elderly patients.


CLINICAL

History

Patients present with a gradually progressive disorder.

* Gait of patients with normal pressure hydrocephalus (NPH) is bradykinetic, broad-based, and shuffling.
* The gait mimics Parkinson disease (PD), with marked difficulty taking the first step (start hesitation) or turning. Freezing episodes also can occur.
* Important features that differentiate NPH from PD include the following:
--- Rigidity, tremor, and slowing of rapid, alternating movements are less commonly observed in NPH than in PD.
--- NPH does not respond significantly to carbidopa/levodopa.
--- No true ataxia or weakness is present in NPH; hence, the gait disturbance in NPH is described as gait apraxia.
* Incontinence is usually urinary but may be fecal. In earlier stages, patients may complain of urgency and frequency rather than true incontinence.
* Dementia is characterized by prominent memory loss and bradyphrenia. It progresses less rapidly than the dementia of Alzheimer disease. Focal deficits and/or seizures are uncommon. Patients with NPH show subcortical cognitive deficits including forgetfulness, decreased attention, inertia, and bradyphrenia distinct from that of Alzheimer disease and other cortical dementias. They also do not present with the "aphasia-apraxia-agnosia syndrome," which is typical for cortical dementia.


Physical

Patients present with gait disorder and dementia.

* Pyramidal tract findings may be present.
* Parkinsonism is present to varying degrees (eg, tremor, hypophonia, hypomimia, bradykinesia, rigidity).


Causes

Possible etiologic factors include head injury, subarachnoid hemorrhage, meningitis, and CNS tumor. Although each of these conditions may cause hydrocephalus, how they are related to subsequent NPH is unclear.


DIFFERENTIAL DIAGNOSES

Alzheimer Disease
Aphasia
Apraxia and Related Syndromes
Confusional States and Acute Memory Disorders
Cortical Basal Ganglionic Degeneration
Dementia in Motor Neuron Disease
Dementia With Lewy Bodies
EEG in Dementia and Encephalopathy
Frontal and Temporal Lobe Dementia
Frontal Lobe Syndromes
Hydrocephalus
Lumbar Puncture (CSF Examination)
Marchiafava-Bignami Disease
Multiple System Atrophy
Paraneoplastic Encephalomyelitis
Parkinson Disease
Parkinson-Plus Syndromes
Pick Disease
Uremic Encephalopathy
Wilson Disease


Other Problems to Be Considered

Toxicity, Hallucinogen
Dementia in Huntington disease
Dementia in Parkinson disease
Dementia in progressive supranuclear palsy
Ethanol-related syndromes
Halstead-Reitan neuropsychological test battery
Postencephalitic parkinsonism
Increased intracranial pressure
Vascular Dementia


WORKUP

Laboratory Studies

* Hyponatremia was reported in a patient with normal pressure hydrocephalus (NPH), presumably due to pressure on the hypothalamus that resulted in a syndrome of inappropriate secretion of antidiuretic hormone. This is not a consistent finding.

Imaging Studies

* CT scan or MRI alone is not sufficient for diagnosis. Distinguishing features of NPH (which excludes hydrocephalus ex vacuo from the diagnosis) include the following:
--- Ventricular enlargement out of proportion to sulcal atrophy (see Image 1)
--- Prominent periventricular hyperintensity consistent with transependymal flow of CSF (see Image 1)
--- Prominent flow void in the aqueduct and third ventricle, the so-called jet sign, (presents as a dark aqueduct and third ventricle on a T2-weighted image where remainder of CSF is bright)
--- Thinning and elevation of corpus callosum on sagittal images
--- Rounding of frontal horns (see Image 2)
--- Lee et al (2005) report that the severity of gait disturbance was negatively correlated with the midbrain diameter as measured on MRI scans.
* Key elements in CT and MRI imaging
--- Hydrocephalus must be present. The modified Evan's ratio (Gyldenstad, 1977) should be greater than 0.31.
--- Presence of extensive cortical atrophy reduces the likelihood of a good response to shunt surgery.
--- Prominent medial temporal cortical atrophy favors a diagnosis of hydrocephalus ex vacuo as opposed to NPH.
--- Presence of abnormalities such as an Arnold Chiari malformation raise the possibility of a congenital hydrocephalus.


Procedures

* Large-volume lumbar puncture: See Surgical Care section.


TREATMENT

Medical Care

* While levodopa/carbidopa has been reported to be of benefit in anecdotal reports, these patients with NPH may represent misdiagnosed cases of parkinsonism. Currently, no definitive evidence exists that levodopa/carbidopa is an effective treatment for normal pressure hydrocephalus (NPH).


Surgical Care

Surgical CSF shunting remains the main treatment modality. Predicting response to shunting requires a large-volume lumbar puncture.
* Patients are given a baseline neuropsychological evaluation (eg, Folstein test or formal neuropsychological evaluation) and a timed walking test.
* Patients then undergo a lumbar puncture with removal of approximately 50 mL of CSF. The above evaluations are repeated 3 hours later.
* A clear-cut improvement in mental status and/or gait predicts a favorable response to shunt surgery. Improvement in gait may be seen in the form of reduced time to walk a fixed distance, reduced gait apraxia, or reduced freezing of gait.
* Videotaping the gait evaluation before and after the large volume lumbar puncture or lumbar drain placement can be helpful in decision making.
* Reduction in bladder hyperactivity also may be a sign of good outcome from shunting. Occasionally, improvement may be delayed and appear 1-2 days after the large-volume lumbar punctures.
* When clinical suspicion is high and the patient is a good candidate for surgery, repeated lumbar punctures are indicated over the next 1-2 days.
* Some clinicians use an indwelling CSF catheter in lieu of repeated lumbar punctures. This method carries a higher risk of meningeal infection but may allow for a more accurate prognosis.
--- In a recent study, Williams et al evaluated 86 patients for possible NPH by (1) CSF pressure monitoring and analysis for percentage of time with A or B waves and (2) controlled CSF drainage for 3 days via a lumbar subarachnoid catheter.
--- Clinical outcome after CSF drainage and shunt surgery were assessed by the change in clinical examination, with grades of none, minor, moderate, or marked change. The outcome analysis in 47 patients after shunt surgery showed moderate or marked clinical improvement in NPH.
--- The authors concluded that (1) clinical response to controlled CSF drainage accurately predicts the outcome after shunt surgery in patients suspected of having NPH and (2) A or B waves poorly predict which patients will respond to shunt surgery.
--- Three days of CSF drainage seem to encompass critical thresholds of CSF volume removal or the duration of CSF pressure reduction necessary for neuronal function to begin returning and symptoms to begin resolving in patients with NPH.
--- Lund et al (2005) found that lumbar infusion testing was not superior to the steady-state plateau pressure for selecting patients for surgery and could increase the risk of missing patients who should benefit from surgery.
* For a more objective assessment, videotape the timed walking test before and after lumbar puncture.

Patients with a good response to the above procedure are candidates for ventriculoperitoneal or ventriculoatrial shunting.
* Best results are reported in patients who have no adverse risk factors; have responded favorably to a large-volume lumbar puncture; and have definite evidence of dementia and ataxia, CT scan or MRI evidence of chronic hydrocephalus, and a normal CSF at lumbar puncture.
* Some evidence indicates that patients with gait disturbance, mild or no incontinence, and mild dementia fare best among shunt surgery patients.

Other modalities for predicting outcome after shunt surgery include isotope cisternography and dynamic MRI studies. No definitive evidence documents superiority of these methods.
* Cardoso et al followed 19 consecutive patients with suspected NPH by means of clinical evaluation, neuropsychological testing, isotope cisternography, CT scanning, and continuous intracranial pressure monitoring. Semiquantitative grading systems were used in the evaluation of the clinical, neuropsychological, and cisternographic assessments. Clinical examination, neuropsychological testing, and CT scanning were repeated 3 months after ventriculoperitoneal shunting. All patients showed abnormal intracranial pressure waves, and all improved after shunting.
* Close correlation was found between the number, peak, and pulse pressures of B waves and the mean intracranial pressure. However, quantification of B waves by means of number, frequency, and amplitude did not help in predicting the degree of clinical improvement postshunting. The most sensitive predictor of favorable response to shunting was enlargement of the temporal horns on CT scan. Furthermore, the size of the temporal horns correlated with mean intracranial pressure. No correlation was found between abnormalities on isotope cisternography and clinical improvement.
* The clinical usefulness of cisternography also was evaluated in a large-scale study (n = 76) by Vanneste et al. The predictive value of a scale based on combined clinical and CT scan criteria was established first, followed by an assessment of the predictive value of cisternography. Predictions based on cisternograms were identical to those of the clinical/CT scan scale in 43%, better in 24%, and worse in 33%. This suggests that cisternography does not improve the diagnostic accuracy of combined clinical and CT scan criteria in patients with presumed normal-pressure hydrocephalus.

Proper patient selection for shunt surgery is important. In a series of 127 patients observed by Vanneste et al, 36% improved after shunt surgery. However, 28% suffered complications, with death or persistent disability in 7% of cases. Other complications included cerebral infarcts, hemorrhages, infection, and seizures.

In summary, an ideal candidate for shunt surgery would show imaging evidence of ventriculomegaly indicated by a frontal horn ratio exceeding 0.50 on imaging studies along with one or more of the following criteria:
* Presence of a clearly identified etiology
* Predominant gait difficulties with mild or absent cognitive impairment
* Substantial improvement after CSF withdrawal (CSF tap test or lumbar drainage)
* Normal-sized or occluded sylvian fissures and cortical sulci on CT or MRI
* Absent or moderate white matter lesions on MRI


Consultations

* Consult with a neurologist for the initial evaluation, including the lumbar puncture.
* Obtain neurosurgical consultation if and when shunt surgery is considered.


MEDICATION

No definitive evidence exists that medication can successfully treat NPH. In patients who are poor candidates for shunt surgery, repeated lumbar punctures in combination with acetazolamide have been tried with mild and transient relief of symptoms.



FOLLOW-UP

Prognosis

The prognosis is poor.
* In a study by Vanneste et al, one of the more comprehensive studies described above, marked improvement was noted in only 21% of patients following shunt surgery. Complication rate was approximately 28%, further emphasizing the importance of careful patient selection.
* In the recent Dutch Normal-Pressure Hydrocephalus Study by Boon et al, concomitant cerebrovascular disease was documented as an indicator of poor prognosis.
* When symptoms of hydrocephalus recur after successful ventriculoperitoneal (V-P) shunt placement, shunt malfunction should be suspected and evaluation for mechanical failure pursued. Catheter migration should be recognized as a correctable cause of shunt malfunction.

Shunt complications
* The incidence of shunt complications is estimated in 30-40% of patients. These include anesthetic complications, intracranial hemorrhage from placement of the ventricular catheter, infection, CSF hypotensive headaches, subdural hematomas, shunt occlusion, and catheter breakage.
* Rapid reduction in ventricular size following the shunt favors complications such as subdural hematoma. Dual-switch valves and programmable valves may reduce the incidence of this complication.


Patient Education

* For excellent patient education resources, visit eMedicine's Dementia Center. Also, see eMedicine's patient education article Normal Pressure Hydrocephalus.


MISCELLANEOUS

Medicolegal Pitfalls

Two potential pitfalls include selecting the wrong patient for surgery and failure to send a patient who is a good candidate to surgery. Given the high risks associated with shunt surgery and its long-term complications, erring on the conservative side is preferred.
* Obtain a definite response to presurgical testing.
* Thorough counseling of the patient and family members is appropriate. Take care to avoid unrealistic expectations.


MULTIMEDIA

T2-weighted MRI showing dilatation of ventricles ...

Media file 1: T2-weighted MRI showing dilatation of ventricles out of proportion to sulcal atrophy in a patient with normal pressure hydrocephalus. The arrow points to transependymal flow.

CT head scan of a patient with normal pressure hy...

Media file 2: CT head scan of a patient with normal pressure hydrocephalus showing dilated ventricles. The arrow points to a rounded frontal horn.


REFERENCES

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KEYWORDS

normal pressure hydrocephalus, NPH, occult hydrocephalus, extraventricular obstructive hydrocephalus, abnormal gait, urinary incontinence, dementia, intracranial pressure, ICP, CSF pressure, cerebrospinal fluid pressure, extraventricular obstructive hydrocephalus, gait apraxia, gait disorder, parkinsonism


CONTRIBUTOR INFORMATION AND DISCLOSURES

Author

Arif Dalvi, MD, Assistant Professor, Department of Neurology, University of Chicago, Co-director of Parkinson's Disease and Movement Disorders Center
Arif Dalvi, MD is a member of the following medical societies: Movement Disorders Society
Disclosure: Nothing to disclose.

Medical Editor

Joseph F Hulihan, MD, Vice President, Medical Affairs, Ortho-McNeil Janssen Scientific Affairs, LLC
Joseph F Hulihan, MD is a member of the following medical societies: American Academy of Neurology, American Clinical Neurophysiology Society, American Epilepsy Society, American Headache Society, and American Medical Association
Disclosure: Johnson & Johnson Salary Employment; Johnson & Johnson Stock Employment

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Nestor Galvez-Jimenez, MD, Program Director of Movement Disorders, Department of Neurology, Division of Medicine, Director of Neurology Residency Training Program, Cleveland Clinic Florida
Nestor Galvez-Jimenez, MD is a member of the following medical societies: American Academy of Neurology, American College of Physicians, and Movement Disorders Society
Disclosure: Nothing to disclose.
CME Editor

Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida School of Medicine, Tampa General Hospital
Selim R Benbadis, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association
Disclosure: Nothing to disclose.
Chief Editor

Nicholas Y Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants
Nicholas Y Lorenzo, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Neurology
Disclosure: Nothing to disclose.