Normal Pressure Hydrocephalus

Normal pressure hydrocephalus (NPH) is a communicating hydrocephalus with normal opening CSF pressure and the triad of gait disturbance, cognitive decline and urinary incontinence.

• Prevalence about 1 to 2% over age 65, underdiagnosed; mean onset 70 years.

• Idiopathic (iNPH, impaired CSF absorption) or secondary (subarachnoid haemorrhage, meningitis, head injury, surgery).

• Potentially reversible cause of dementia.

• Comorbid Alzheimer pathology and vascular disease are frequent.

• Gait: broad based, magnetic, slow, short steps, small turns, poor balance ("feet stuck to the floor"); appears first and responds best.

• Cognition: subcortical (slowed processing, apathy, executive and attention deficits, memory retrieval).

• Urinary urgency and later incontinence; faecal incontinence late.

• Absence of papilloedema and headache.

• MRI/CT: ventriculomegaly (Evans index over 0.3) out of proportion to sulcal atrophy, disproportionately enlarged subarachnoid space hydrocephalus (DESH), callosal angle under 90 degrees, periventricular signal changes, flow void in aqueduct.

• Large volume lumbar puncture (tap test, 30 to 50 mL): improvement in gait speed (10 metre walk, Timed Up and Go) within hours to 2 days; sensitivity 50 to 60%, specificity high. Opening pressure 5 to 18 cmH2O.

• Extended lumbar drainage (external lumbar drain 8 to 10 mL/h for 3 days) improves prediction (sensitivity 80 to 100%).

• CSF infusion test (outflow resistance over 12 to 18 mmHg/mL/min).

• Exclude Parkinson disease, vascular dementia, Alzheimer disease, spinal stenosis, peripheral neuropathy, depression.

• CSF shunting (ventriculoperitoneal or lumboperitoneal) with programmable valve: improvement in 60 to 80% in carefully selected patients, with gait improving most; adjustable valve allows titration (set initial pressure 5 to 8 cmH2O, lower if no benefit).

• Perioperative cefazolin 2 g IV.

• Complications 5 to 15%: over drainage with subdural haematoma, infection (3%), obstruction, seizure.

• Acetazolamide 250 mg two to three times daily has been used to bridge when surgery is not possible (limited evidence).

• Physiotherapy after shunting, treat vascular risk factors, follow up with MRI/CT if new symptoms.

• Review benefits at 3 and 12 months, valve adjustments.