Normal Pressure Hydrocephalus

What Normal Pressure Hydrocephalus is

Normal Pressure Hydrocephalus (NPH, ICD-11 6D85.6) is an abnormal accumulation of Cerebrospinal Fluid (CSF) in the brain ventricles, causing ventricular enlargement. The CSF pressure is, paradoxically, in the normal range, hence the name. NPH typically affects adults aged 60 and over, with around 5 in every 10,000 people affected. It is potentially treatable, which is the most important reason to recognise it.

The classic triad

The triad described by Hakim and Adams in 1965 remains the diagnostic frame:

1. Gait disturbance ("magnetic" gait, with feet appearing stuck to the floor; short, shuffling steps; wide base, often with falls);
2. Urinary incontinence (urgency, frequency, then incontinence);
3. Cognitive impairment (mainly slowed processing, executive dysfunction, attention, with relatively preserved memory).

Not everyone has all three features. Gait is the most reliable, often the first, and the most responsive to treatment.

How it is diagnosed

• Clinical history with attention to the triad;
• Examination including a witnessed walking test;
• Magnetic Resonance Imaging showing enlarged ventricles disproportionate to the degree of cortical atrophy (the Evans index helps quantify this), often with the DESH sign (disproportionately enlarged subarachnoid space hydrocephalus);
• Lumbar Puncture "tap test", with removal of 30 to 50 mL of CSF, followed by re-assessment of gait and cognition over the following hours. Improvement after the tap supports the diagnosis;
• Extended lumbar drainage over 3 to 5 days, in selected cases where the tap test is equivocal;
• Specialist neurosurgical or neurology assessment.

Treatment

The mainstay of treatment is ventriculoperitoneal (VP) shunt insertion. A shunt drains excess CSF from the brain ventricles into the abdominal cavity, where it is reabsorbed. Surgery is performed by a neurosurgical team.

Outcomes are best when:

• The triad is clear, particularly with gait disturbance dominant;
• Symptom duration is shorter (under 2 years);
• The tap test shows clear improvement;
• Imaging shows the typical pattern.

Around 60 to 80 per cent of carefully selected patients improve substantially after shunt surgery. Gait responds best, followed by cognition, with incontinence responding least reliably. Improvement is often dramatic in the first weeks.

Risks of shunt surgery

The procedure carries risks including infection, bleeding, shunt malfunction requiring revision, and over-drainage causing headache or subdural collections. The risks are weighed carefully against the potential for substantial improvement. Older age and frailty influence the decision.

When to consider NPH

NPH should be considered in any older adult with:

• Gait change as the first symptom of cognitive decline;
• Magnetic gait or apraxic gait;
• Disproportionate ventricular enlargement on brain imaging;
• Cognitive picture dominated by slowed processing rather than dense memory loss.

NPH is often missed when the cognitive features are interpreted as Alzheimer's Disease without adequate attention to the gait and imaging.

Where to get assessed

UK neurosurgical units assess and treat NPH; referral is via your GP or neurologist. The Dementia Service can provide structured cognitive assessment to clarify the picture before onward neurosurgical referral.