Synonyms: chronic hydrocephalus, extraventricular obstructive hydrocephalus

Normal pressure hydrocephalus (NPH) describes the condition of ventricular dilatation in the absence of raised CSF pressure on lumbar puncture, characterised by a triad of gait abnormality, urinary (usually) incontinence and dementia. The importance of this diagnosis lies in the fact that it is a potentially reversible cause of dementia, accounting for up to 6% of dementias.¹

It was first described by Hakim and Adams in 1965.² The three patients identified in the original series had dilation of the cerebral ventricles without an increase in CSF pressure on lumbar puncture.

Further research has revealed that intracranial pressure (ICP) does indeed rise in the initial phase and that subsequent ventricular enlargement results in the ICP returning to normal. CSF pressure, as measured during an isolated lumbar puncture procedure, is a poor assessment of CSF dynamics in these patients, many of whom do indeed exhibit a rise in pressure, albeit on an intermittent basis.³

Current studies suggest that CSF pressure is controlled by alterations in spinal compliance or decrease in CSF absorption at the sagittal sinus. Four subtypes of NPH have thus been identified depending on whether one or other or both of these mechanisms are operating. This may have important implications in terms of management.⁴

Aetiology

The cause of normal pressure hydrocephalus (NPH) is not always obvious. In 50% of cases, there is no known preceding cause (idiopathic NPH). In the remainder, it may be secondary to:

• Subarachnoid haemorrhage.
• Meningitis.
• Head injury.
• Central nervous system (CNS) tumour.

All of these conditions can cause hydrocephalus but the pathological process that leads to NPH is not clear. These patients must be differentiated from patients whose ventricular enlargement is a result of shrinkage of surrounding tissue, as in Alzheimer's disease for example.

See separate article Hydrocephalus for more detail.

Epidemiology

The condition occurs mainly in elderly patients. Prevalence ranges from 3.3 per 100,000 for people 50 to 59 years of age, to 49.3 per 100,000 for people 60 to 69 years of age, to 181.7 per 100,000 for people 70 to 79 years of age.⁵

Some researchers maintain that similar CSF hydrodynamic changes are seen in some hydrocephalic children.^3,6 There is no predominance of gender.

Presentation

Symptoms

The (gradually progressive) classic triad of symptoms is:⁵

1. Gait disturbance - this is due to distortion of the corona radiata by the dilated ventricles. This area contains the sacral motor fibres than innervate the legs. Movements are slow, broad-based and shuffling. The clinical impression is thus one of Parkinson's disease, except that rigidity and tremor are less marked and there is no response to carbidopa/levodopa. Freezing episodes can also occur. True ataxia and weakness is absent and the gait disturbance is referred to as gait apraxia.
2. Sphincter disturbance - this is also due to involvement of the sacral nerve supply. Urinary incontinence is predominant although bowel incontinence can also occur.
3. Dementia - this is due to distortion of the periventricular limbic system. The prominent features are memory loss, inattention, inertia and bradyphrenia (slowness of thought). The dementia progresses less rapidly than that seen with Alzheimer's disease.

Signs

• Pyramidal tract signs may be present.
• Reflexes may be brisk.
• Papilloedema is absent (but there has been found to be an association with glaucoma, so glaucomatous optic disc changes may be noticed).⁷

Investigations⁶

• Neuroimaging - MRI or CT scanning may show ventricular enlargement out of proportion to sulcal atrophy and periventricular lucency. Isotope cisternography may also be useful to demonstrate CSF dynamics, particularly when attempting to predict which patients will benefit from surgery.⁸
• Large-volume lumbar puncture (spinal or CSF tap test)⁹ - CSF pressure will be normal, or intermittently raised. Furthermore, the effect of the lumbar puncture is assessed looking at improvement of the patient's symptoms which can last for a period of days to weeks. The value of this test is limited in diagnosing normal pressure hydrocephalus (NPH) but may be useful in narrowing the differential diagnosis. If it is positive and symptoms do improve, it can be used as a predictor of positive operative outcome (see below).
• Intraventricular monitoring - in NPH, this may show a particular pattern characterised by beta waves - see 'Management', below.¹⁰
• Lumbar infusion test (intrathecal infusion test)⁹ - the CSF absorptive capacity is tested with a fluid challenge. An abnormal, sustained rise in CSF suggests NPH.

Although the invasive tests carry theoretical risks (infection, post-procedure headache, bleeding, localised pain and nerve root damage), evidence suggests that these are actually very safe procedures.⁹ In these patients, it is also useful to check the serum sodium, as hyponatraemia has been reported.¹¹

Diagnosis

This is based on the clinical triad described above, in the absence of papilloedema, backed by neuroimaging (specific criteria are defined) without evidence of raised intracranial pressure (ICP) and with evidence of symptom improvement on lumbar puncture.⁹ Accurate diagnosis is the key to treatment success.¹

Differential diagnosis⁶

• Alzheimer's disease.
• Aphasia.
• Apraxia and related syndromes.
• Confusional states and acute memory disorders.
• Cortical basal ganglionic degeneration.
• Dementia with Lewy bodies.
• Dementia in motor neurone disease.
• EEG in dementia and encephalopathy.
• Frontal lobe syndromes.
• Frontal and temporal lobe dementia.
• Hydrocephalus.
• Marchiafava-Bignami syndrome (gait disturbance and dementia, usually in alcoholics, thought to be due to bilateral reduction cerebral blood flow).
• Multi-infarct dementia.
• Multiple system atrophy.
• Paraneoplastic encephalomyelitis.
• Parkinson's disease.
• Parkinson-plus syndromes.
• Pick's disease.
• Uraemic encephalopathy .
• Wilson's disease.

Management

The identification and treatment of normal pressure hydrocephalus (NPH) is worthwhile, providing patients are carefully selected, as it remains one of the truly reversible causes of dementia.

Medical

Medical treatment of NPH includes acetazolamide and repeated lumbar puncture. These methods are rarely successful long-term and are usually used as temporary deferment measures or in patients who are too ill for surgery.

Surgical³

The mainstay of treatment is surgical insertion of a CSF shunt.^5,9 This could be to the peritoneum, the right atrium or, more recently, via external lumbar drainage. Selection of patients for surgery is important, as exposing patients to shunt-related complications such as mechanical failure or infection is unwarranted, unless a good clinical outcome is expected. Various parameters are used to predict which patients will benefit from surgery, but there is insufficient evidence for their efficacy.

Features suggesting a good outcome include:

• Presence of a clearly identified aetiology.
• Predominant gait difficulties with mild cognitive impairment.
• Normal-sized or occluded Sylvian fissures and cortical sulci on CT or MRI.
• Absent or moderate white matter lesions on MRI.

Insertion of a ventriculoperitoneal shunt is the first-line procedure, with ventriculo-atrial shunting being used as an alternative.

Prognosis

Prognosis is variable, even after shunt surgery. The combined rate of permanent neurological deficit or death has been reported as 6%, with the need for additional surgery occurring in 22%.^1,5 Over a period of 10 years, shunt revision was required in approximately 1 in 2-3 cases. There is good long-term survival of 39% after 5 years.

Complications of shunt surgery are found in up to 10% and include:

• Shunt occlusion
• Catheter breakage
• CSF hypotensive headaches
• Cerebral infarct
• Haemorrhage
• Infection
• Seizures
• Death

Document references

1. Pujari S, Kharkar S, Metellus P, et al; Normal pressure hydrocephalus: long-term outcome after shunt surgery. J Neurol Neurosurg Psychiatry. 2008 Nov;79(11):1282-6. Epub 2008 Mar 20. [abstract]
2. Adams RD, Fisher CMm, Hakim S, et al; Symptomatic occult hydrocephalus with "normal" cerebrospinal-fluid pressure. A treatable syndrome. N Engl J Med. 1965 Jul 15;273:117-26.
3. Bret P, Guyotat J, Chazal J; Is normal pressure hydrocephalus a valid concept in 2002? A reappraisal in five questions and proposal for a new designation of the syndrome as "chronic hydrocephalus". J Neurol Neurosurg Psychiatry. 2002 Jul;73(1):9-12. [abstract]
4. Hamlat A, Adn M, Sid-ahmed S, et al; Theoretical considerations on the pathophysiology of normal pressure hydrocephalus (NPH) and NPH-related dementia. Med Hypotheses. 2006;67(1):115-23. Epub 2006 Mar 13. [abstract]
5. Shprecher D, Schwalb J, Kurlan R; Normal pressure hydrocephalus: diagnosis and treatment. Curr Neurol Neurosci Rep. 2008 Sep;8(5):371-6. [abstract]
6. Dalvi A et al, Normal Pressure Hydrocephalus, Medscape, Oct 2010
7. Chang TC, Singh K; Glaucomatous disease in patients with normal pressure hydrocephalus. J Glaucoma. 2009 Mar;18(3):243-6. [abstract]
8. Factora R; When do common symptoms indicate normal pressure hydrocephalus? Cleve Clin J Med. 2006 May;73(5):447-50, 452, 455-6 passim. [abstract]
9. Lumbar infusion test for the investigation of normal pressure hydrocephalus, NICE Interventional Procedure Guideline (June 2008)
10. Rao G; Neurological Monitoring. Indian J. Anaesth. 2002; 46 (4) : 304-314.
11. Chou CY, Liu JH, Wang SM, et al; Hyponatraemia in patients with normal pressure hydrocephalus. Int J Clin Pract. 2009 Mar;63(3):457-61. [abstract]