Correct Answer: D. Normal pressure hydrocephalus
Normal pressure hydrocephalus (NPH) is a classic triad of gait disturbance (magnetic gait), urinary incontinence, and dementia — often remembered as "wet, wacky, wobbly." The discriminating feature here is the combination of all three symptoms together with a history of multiple falls, which is pathognomonic for NPH. Unlike other dementias, NPH presents with a characteristic shuffling, broad-based gait (magnetic gait) that precedes cognitive decline. The pathophysiology involves impaired CSF absorption despite normal opening pressure, leading to ventricular enlargement and periventricular white matter changes. In elderly Indian patients, NPH is often underdiagnosed because it mimics Parkinson disease or primary dementia. The key diagnostic clue is the triad occurring together — dementia alone, or gait disorder alone, would not be NPH. Diagnosis is confirmed by MRI showing ventricular enlargement with normal sulci and CSF tap test (lumbar puncture with 30–50 mL CSF removal followed by gait assessment). The reversibility of symptoms after ventriculoperitoneal shunt placement distinguishes NPH from other progressive dementias. This is a high-yield diagnosis because it is one of the few treatable causes of dementia in India, yet frequently missed.
Why the other options are wrong
A. Frontotemporal dementia — Frontotemporal dementia presents with behavioral change and personality disturbance as the primary feature, not gait disturbance or incontinence. While behavioral change is mentioned in the stem, the combination of gait disorder (falls), incontinence, and dementia together is not typical of FTD. FTD patients have normal gait and normal pressure CSF. This is an NBE trap using 'behavioral change' as a red herring. B. Creutzfeldt-Jakob disease — CJD presents with rapidly progressive dementia (weeks to months) with myoclonus, ataxia, and visual disturbances, not the insidious triad of gait-incontinence-dementia. CJD is rare in India and typically affects younger patients. The absence of myoclonus and rapid progression timeline rules out CJD. CJD does not cause the characteristic magnetic gait of NPH. C. Parkinson disease — While Parkinson disease causes gait disturbance and can present with cognitive decline, it does not classically present with urinary incontinence as an early feature. Parkinsonism shows resting tremor, rigidity, and bradykinesia — none mentioned in the stem. The triad of gait-incontinence-dementia is not Parkinsonian; NPH's magnetic gait is distinct from Parkinsonian shuffling. This is a common trap confusing gait disorders.
High-Yield Facts
- NPH triad: gait disturbance (magnetic gait), urinary incontinence, dementia — mnemonic 'wet, wacky, wobbly'
- Magnetic gait in NPH is broad-based, shuffling, with feet appearing 'stuck to the floor' — distinct from Parkinsonian gait
- MRI findings in NPH: ventricular enlargement (Evans index >0.3) with normal or tight sulci (key discriminator from atrophy)
- CSF tap test: lumbar puncture with removal of 30–50 mL CSF; improvement in gait within 24–48 hours predicts shunt response
- NPH is reversible if diagnosed early and shunt placed before irreversible white matter damage — only treatable dementia in this differential
- Opening pressure in NPH is normal (10–20 cm H₂O) despite ventricular enlargement — distinguishes from obstructive hydrocephalus
Mnemonics
Wet, Wacky, Wobbly Wet = urinary incontinence; Wacky = dementia/behavioral change; Wobbly = gait disturbance (magnetic gait). All three together = NPH. Use this at the bedside when you see an elderly patient with this triad. Evans Index >0.3 Ratio of maximal ventricular width to maximal cranial width >0.3 on CT/MRI = ventricular enlargement. In NPH, this is enlarged but sulci are NOT dilated (unlike atrophic dementia). This imaging pearl separates NPH from Alzheimer disease.
NBE Trap
NBE pairs 'behavioral change' with frontotemporal dementia to distract from the combination of gait disorder + incontinence + dementia, which is pathognomonic for NPH. Students who focus only on behavioral change miss the complete clinical picture.
Clinical Pearl
In Indian elderly patients, NPH is often misdiagnosed as Parkinson disease or primary dementia and left untreated. A simple bedside clue: ask the patient to walk — if they shuffle with a broad base and feet seem "glued to the floor" (magnetic gait), and they have incontinence + dementia, order an MRI and CSF tap test immediately. Early shunt placement can reverse symptoms and restore independence, making this a critical diagnosis not to miss.
_Reference: Harrison Ch. 452 (Dementia); Robbins Ch. 28 (CNS pathology); KD Tripathi Ch. 12 (Neuropharmacology)_