11th August 2024

Normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) was historically described as the triad of gait disturbance, urinary incontinence and cognitive slowing as a result of hydrocephalus without raised cerebrospinal fluid pressure. The aide-memoire “wobbly, wet and wacky” may have come up in medical school! Clinical features typically develop gradually over years.

The reported incidence of NPH is variable as there are different diagnostic criteria. The pathophysiology is not well understood, but the underlying processes are thought to drive formation of a communicating hydrocephalus with resultant ischaemic insult to subcortical and periventricular structures including the basal ganglia.

Risk factors are predominantly age >65 and vascular, thought to be related to effects on compliance of cerebral blood vessels that, in turn, regulate the flow of CSF.

Diagnosis and management of NPH

Gait disturbance is the key and usually first symptom noticed and is typically small stepped, slow, hesitant, wide based and magnetic (‘stuck to the floor’), with difficulties in making 180 degree turns in 3 or fewer steps.

Lumbar puncture has both a diagnostic and therapeutic role – specifically, pressure measured by manometry should be normal. Large volume CSF removal (40-50 ml) can be done with cognitive testing and gait assessment pre- and post-therapeutic lumbar puncture; cases that respond to this may represent candidates for further lumbar drainage, although identifying this group of individuals can be challenging.

A trial of levodopa should not yield gait improvement (excluding Parkinson’s disease) and brain imaging can demonstrate ventriculomegaly which is disproportionate to sulcal atrophy, distinguishing it from global cerebral atrophy. There may also be evidence of periventricular white matter change, although imaging can also be normal. A space-occupying lesion with obstruction would exclude the diagnosis of NPH.