Normal-Pressure Hydrocephalus (NPH)
The most likely diagnosis is D) Normal-pressure hydrocephalus. This 75-year-old man presents with the classic triad of NPH: progressive gait disturbance (specifically described as "magnetic gait" with wide base), memory loss (cognitive impairment), and urinary incontinence over 6 months 1.
Why NPH is the Clear Answer
The clinical presentation is pathognomonic for NPH based on several key features:
Gait characteristics are diagnostic: The description of "magnetic gait" with a wide base is the hallmark of NPH and typically appears first among the triad symptoms 2, 3. This apractic/ataxic gait pattern—where patients appear to have their feet stuck to the floor—is highly specific for NPH and distinguishes it from other neurodegenerative conditions 1.
Temporal progression supports NPH: The 6-month progressive course with gait disturbance appearing early, followed by cognitive impairment and incontinence, follows the typical NPH presentation pattern 1, 2. Gait tends to be affected first and more severely than other domains in idiopathic NPH 2.
Age and symptom constellation: NPH has an estimated prevalence of 3.7% in patients over 65 years and represents a potentially reversible cause of dementia following CSF diversion 1. The complete triad presentation in this elderly patient strongly suggests NPH.
Why Other Options Are Less Likely
Parkinson's disease (A): While Parkinson's can cause gait disturbance and cognitive decline, the "magnetic gait" with wide base is not characteristic. Parkinsonian gait is typically narrow-based with shuffling steps, festination, and reduced arm swing. The prominent early urinary incontinence and specific gait pattern argue against Parkinson's.
Dementia (B): Primary dementia syndromes (Alzheimer's, vascular dementia) do not typically present with the specific magnetic gait pattern or the full triad in this temporal sequence. Gait disturbance in NPH precedes and is more severe than cognitive impairment, which is the opposite of most primary dementias 2.
Stroke (C): Acute stroke would have sudden onset rather than 6-month progressive course. Multiple small strokes (vascular dementia) could cause similar symptoms but would show a stepwise decline pattern and lack the characteristic magnetic gait.
Cerebellar tumor (E): Would typically present with ataxia, but the gait pattern would be different (wide-based cerebellar ataxia without the magnetic quality), and would likely have additional cerebellar signs (dysmetria, nystagmus, dysarthria) and possibly increased intracranial pressure symptoms.
Critical Diagnostic Considerations
Imaging is essential: The diagnosis requires confirmation with neuroimaging showing ventriculomegaly, narrowed posterior callosal angle, effaced sulci along high convexities, and widened sylvian fissures 1. MRI brain without contrast is the preferred initial imaging modality as it has higher sensitivity for periventricular white matter changes and can detect disproportionately enlarged subarachnoid-space hydrocephalus (DESH) 1, 3.
CSF tap test confirms diagnosis: The CSF tap test is a key diagnostic tool where both objective and subjective improvements in symptoms help identify patients likely to benefit from shunt surgery 2, 4. Note that CSF pressure may be normal in NPH patients, and absence of low pressure should not exclude the diagnosis 4.
Important Clinical Pitfall
Comorbid cervical stenosis is common and may coexist with NPH in elderly patients, potentially causing overlapping symptoms of gait disturbance and incontinence 5. Cervical spine imaging should be considered if myelopathic findings are present on examination, as cervical stenosis can mask the effect of CSF diversion and may require surgical decompression in addition to shunt placement 5.
NPH is potentially reversible with CSF diversion (shunting), making accurate diagnosis critical for patient outcomes 1, 3. Any patient showing improvement after CSF drainage deserves therapeutic intervention 4.