Normal Pressure Hydrocephalus

Definition. NPH is a syndrome of gait disturbance, cognitive impairment and urinary incontinence (Hakim– Adams triad) with ventriculomegaly but a normal CSF opening pressure. It is idiopathic in most older people, or secondary to subarachnoid haemorrhage, head injury, meningitis or infarction.

Gait disturbance is the earliest and most important feature. It is magnetic or “glue-footed” with reduced stride length, reduced step height, broad base and poor balance. Unlike Parkinson’s disease, it does not respond to external cues or to levodopa.

Cognitive impairment is frontal-subcortical — inattention, slowed psychomotor speed, impaired recall more than recognition, and visuospatial dysfunction. Memory and orientation are relatively preserved, which separates it from Alzheimer’s disease.

Urinary dysfunction begins as frequency and urgency and progresses to urge incontinence and then total incontinence as frontal control is lost. Mechanisms are a small bladder capacity (mean 200 mL) and a hyperactive detrusor. Faecal incontinence occurs late.

Diagnosis. CT/MRI shows ventricular enlargement out of proportion to atrophy (Evans index >0.3, DESH pattern). Patient selection is crucial: a positive CSF tap test, external lumbar drainage or raised CSF outflow resistance predicts shunt response. Age is not a prognostic factor.

Treatment. Ventriculoperitoneal shunting is standard care and succeeds in about 80% of well-selected patients — gait improves in 81–86%, bladder control in 70%, cognition in only 40–44%. Serious adverse event risk is 11%: shunt infection (a neurosurgical emergency), subdural effusion or haematoma, obstruction, over-drainage and hearing loss.

PENS trial (NEJM 2025) — the first double-blind, placebo-controlled trial of shunting in iNPH (n=99; open valve 110 mmH O vs placebo setting >400 mmH O). At 3 months, shunting significantly improved gait velocity 2 2 and Tinetti gait-and-balance score, but showed no significant benefit in cognition (MoCA) or incontinence. This confirms that gait is the shunt-responsive domain and that response to temporary CSF drainage should drive patient selection.