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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.
It was first described by Hakim and Adams in 1965. The three patients identified in the original series had dilation of the cerebral ventricles without an increase in CSF pressure on lumbar puncture.
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.
The cause of 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.
- Head injury.
- Central nervous system (CNS) tumour.
All these conditions can cause hydrocephalus but the pathological process which 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 Hydrocephalus article.
The condition occurs mainly in elderly patients. Prevalence ranges from 3.3 per 100,000 for people aged 50 to 59 years, to 49.3 per 100,000 for people aged 60 to 69 years, to 181.7 per 100,000 for people aged 70 to 79 years.
The (gradually progressive) classic triad of symptoms is:
- 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 are absent and the gait disturbance is referred to as gait apraxia.
- Sphincter disturbance - this is also due to involvement of the sacral nerve supply. Urinary incontinence is predominant although bowel incontinence can also occur.
- 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.
- 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).
- 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.
- Large-volume lumbar puncture (spinal or CSF tap test).CSF pressure will be normal, or mildly elevated.The value of this test is limited in diagnosing NPH but may be useful in narrowing the differential diagnosis.
- Intraventricular pressure monitoring.
- Lumbar infusion test (intrathecal infusion test).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. In these patients, it is also useful to check the serum sodium, as hyponatraemia has been reported.
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. Accurate diagnosis is the key to treatment success.
- Alzheimer's disease.
- 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.
- Frontotemporal dementia (Pick's disease).
- 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.
- Uraemic encephalopathy .
- Wilson's disease.
The identification and treatment of NPH is worthwhile, providing patients are carefully selected, as it remains one of the truly reversible causes of dementia.
Medical treatment of NPH includes carbonic anhydrase inhibitors (acetazolamide) and repeated lumbar puncture. These methods are rarely successful long-term. Carbonic anhydrase inhibitors and serial lumbar punctures are not advisable as alternative treatments, except for a limited time in medically inoperable patients.
The mainstay of treatment is surgical insertion of a CSF shunt.[3, 6] 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.
Insertion of a ventriculoperitoneal shunt is the first-line procedure, with ventriculo-atrial shunting being used as an alternative.
Complications of shunt surgery are found in up to 10% and include:
- Shunt occlusion
- Catheter breakage
- CSF hypotensive headaches
- Cerebral infarct
70% to 90% of patients obtain a lasting clinical benefit from shunting compared to their pre-operative state.
Further reading and references
; Normal pressure hydrocephalus: long-term outcome after shunt surgery. J Neurol Neurosurg Psychiatry. 2008 Nov79(11):1282-6. Epub 2008 Mar 20.
; Theoretical considerations on the pathophysiology of normal pressure hydrocephalus (NPH) and NPH-related dementia. Med Hypotheses. 200667(1):115-23. Epub 2006 Mar 13.
; Normal pressure hydrocephalus: diagnosis and treatment. Curr Neurol Neurosci Rep. 2008 Sep8(5):371-6.
; Glaucomatous disease in patients with normal pressure hydrocephalus. J Glaucoma. 2009 Mar18(3):243-6.
; When do common symptoms indicate normal pressure hydrocephalus? Cleve Clin J Med. 2006 May73(5):447-50, 452, 455-6 passim.
; NICE Interventional Procedure Guidance, June 2008
; The differential diagnosis and treatment of normal-pressure hydrocephalus. Dtsch Arztebl Int. 2012 Jan109(1-2):15-25
; Hyponatraemia in patients with normal pressure hydrocephalus. Int J Clin Pract. 2009 Mar63(3):457-61.