Synopsis
Recognise the characteristic gait-led syndrome and DESH imaging pattern, separate idiopathic from secondary disease and common mimics, and interpret tap-test results without excluding treatable disease after a negative test.
- Think gait first: iNPH typically causes a small-step, shuffling, broad-based, unstable gait with difficulty initiating and turning; gait is often the earliest and most treatment-responsive domain.
- The triad is gait disturbance, cognitive impairment and urinary urgency or incontinence, but all three need not be equally advanced before referral.
- Ventriculomegaly is necessary context, not proof. DESH combines an Evans index of at least 0.3 with tight high-convexity or midline subarachnoid spaces and enlarged Sylvian fissures.
Key red flags
Abrupt or fluctuating reduced consciousness, new focal weakness, seizure, severe headache or repeated vomiting suggests an acute process rather than uncomplicated iNPH.
Fever, meningism, recent neurosurgery or a CSF device raises infection and requires urgent device-aware assessment.
A known shunt with rapid symptom recurrence, vomiting, drowsiness, wound inflammation or abdominal symptoms may have failed or become infected.
Prominent early visual, bulbar, cerebellar, sensory-level or upper-motor-neurone findings require a broader structural and neurological differential.
An obvious preceding SAH, meningitis, head injury or congenital hydrocephalus means the syndrome is secondary or developmental, not idiopathic NPH.
Falls and urinary symptoms can cause immediate harm even in a chronic syndrome; assess injury, retention, infection and safeguarding while the diagnosis is investigated.
Sudden coma, focal deficit, seizure or vomiting is not explained by routine iNPH progression. Investigate immediately for acute hydrocephalus, bleeding, stroke, infection or shunt complication.
Reasoning priorities
Document the dominant impairment and create a reproducible baseline before and after CSF drainage.
Use a timed up-and-go or short straight-walk test with recorded steps, speed, turn quality and video where appropriate. A meaningful change must exceed day-to-day variability and be interpreted with pain, fatigue and practice effects.
Worked reasoning
An older adult has progressive magnetic gait, executive slowing and urgency, MRI shows DESH, but no improvement is seen immediately after a tap test.
- Confirm that more than one triad symptom is present, no preceding cause is obvious and no competing disorder completely explains the disability.
- Review MRI for true DESH—ventriculomegaly with tight high-convexity or midline spaces and enlarged Sylvian fissures—rather than using ventricular size alone.
- Check that gait and cognition were measured objectively before drainage and reassess on the following day and, through the specialist pathway, more than once within the first week.
- Do not exclude iNPH because the immediate tap response is negative; discuss possible false negativity and further specialist testing or shunt selection in context.
- Balance potential functional gain against comorbidity and shunt risks, agree meaningful patient-centred goals, and retain alternative diagnoses if response remains incomplete.