Normal Pressure Hydrocephalus
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Direct answer
Normal pressure hydrocephalus is a form of communicating hydrocephalus in older adults, causing the triad of gait disturbance, urinary incontinence and cognitive decline with a normal lumbar opening pressure. The classic MRI pattern is ventricular enlargement out of proportion to sulcal atrophy, and a positive lumbar tap test predicts benefit from shunting. Ventriculoperitoneal shunting is the established treatment, and gait is the component most reliably improved.
What you must remember
- Wet, wobbly and wacky: urinary incontinence, magnetic gait and subcortical dementia; the triad is a clinical aid rather than a full diagnosis.
- Gait: short shuffling steps with feet apparently stuck to the floor, a wide base and difficulty turning, often with reduced arm swing.
- Evans index: frontal horn width over the maximal inner skull width greater than 0.3 on axial imaging.
- DESH pattern: disproportionately enlarged subarachnoid space hydrocephalus, with tightened high convexity sulci on MRI.
- Tap test: removal of about 30 to 50 mL of CSF by lumbar puncture, followed by gait improvement within a day, predicts shunt response.
- Secondary NPH: may follow subarachnoid haemorrhage, meningitis or head injury, which gives a clearer history.
- Shunt response: gait responds best, urinary symptoms less reliably, and cognition least of all.
Working through an older man losing balance and memory
A 74-year-old retired teacher has two years of slowing gait, urinary urgency and forgetfulness. On examination he has a wide-based, short-stepped gait with difficulty starting and turning, reduced arm swing and no tremor.
- Confirm the triad and imaging: the triad suggests normal pressure hydrocephalus, and MRI shows ventricular enlargement with an Evans index above 0.3 and a DESH pattern.
- Measure the pressure: lumbar opening pressure is measured and is within the normal range.
- Perform the tap test: gait is assessed before and after removal of about 40 mL of CSF, using a timed walk and a standard gait score, and improvement supports shunting.
- Look for competing disease: before surgery, the team looks for coexisting Alzheimer or Parkinson disease, which reduces the chance of benefit.
- Record a baseline: a baseline neuropsychological assessment is recorded to measure any later change.
- Use a drainage trial if equivocal: if the tap test is equivocal, a continuous lumbar drainage trial over several days is an alternative.
- Discuss surgery: shunt surgery is discussed with the patient and family, including the risks of infection, blockage and overdrainage.
Where the examiner tests pressure rather than ventricles
Ventricular enlargement alone is common in old age, so the examiner expects the candidate to check the opening pressure, the gait pattern and the tap test first.
- Trap: diagnosing normal pressure hydrocephalus from ventricular enlargement alone. Correct: look for the normal opening pressure, the gait pattern and the tap test before making the diagnosis.
- Trap: expecting a shunt to help dementia with incontinence and gait change in Alzheimer or Parkinson disease. Correct: the shunt is unlikely to help in that setting.
- Trap: promising that memory will improve after surgery. Correct: cognition is the least responsive part of the triad, so the family should be told that memory may not improve.
- Trap: dismissing headache, vomiting or worsening gait after a shunt. Correct: these need urgent review for blockage or overdrainage, which are frequent examiner questions.
Frequently asked questions
What is the classic triad of normal pressure hydrocephalus?
The classic triad of normal pressure hydrocephalus is gait disturbance, urinary incontinence and cognitive decline, often summarised as wet, wobbly and wacky. Gait disturbance is usually the earliest and most treatable component, and the triad is typical of older adults with a normal lumbar opening pressure.
What does a positive tap test show in normal pressure hydrocephalus?
A positive tap test in normal pressure hydrocephalus is improvement in gait after removal of roughly 30 to 50 mL of CSF by lumbar puncture. It predicts a good response to ventriculoperitoneal shunting, although a negative test does not fully exclude benefit and a lumbar drainage trial may be considered.
Which MRI measure supports the diagnosis of normal pressure hydrocephalus?
The Evans index supports normal pressure hydrocephalus when the maximal width of the frontal horns exceeds 0.3 of the maximal inner skull width. A pattern of disproportionately enlarged subarachnoid space hydrocephalus further supports the diagnosis.
What complications follow ventriculoperitoneal shunting for normal pressure hydrocephalus?
Ventriculoperitoneal shunting for normal pressure hydrocephalus can cause infection, shunt blockage and overdrainage, which may lead to subdural haematoma. Shunt malfunction presents with headache, vomiting or worsening gait, and needs urgent neurosurgical review.