Normal pressure hydrocephalus is the classically treatable dementia mimic. The triad — gait apraxia, urinary incontinence, and cognitive impairment — was first described by Hakim and Adams in 1965. The disease is uncommon but consequential because, when identified, ventriculoperitoneal shunting can substantially improve symptoms.
The Hakim triad — often summarized as "wet, wobbly, weird":
Gait apraxia ("wobbly"): often the dominant and earliest symptom. The patient walks with a wide base, short shuffling steps, sometimes described as "magnetic" — feet seem stuck to the floor with difficulty initiating each step. Distinct from cerebellar ataxia (no past-pointing or finger-to-nose dysmetria) and from Parkinsonian gait (no rest tremor, often no rigidity, no asymmetric onset).
Urinary incontinence ("wet"): often emerges with gait. Urinary urgency and frequency progressing to frank incontinence.
Cognitive impairment ("weird"): typically executive dysfunction, processing speed slowing, attention difficulties — frontal-subcortical pattern. Often relatively preserved memory for recall. Cognitive symptoms typically less dominant than gait early in disease.
The clinical recognition that matters: NPH should be suspected in any older patient with gait disturbance disproportionate to memory complaints, particularly with urinary symptoms. Many NPH patients are diagnosed with general "dementia" and miss the opportunity for treatment because the gait pattern is not specifically noticed.
Imaging: MRI typically shows ventriculomegaly out of proportion to cortical atrophy. Specific features: Evans index >0.3 (ratio of frontal horn width to maximal skull width), callosal angle <90 degrees on coronal images, periventricular white matter changes, sometimes flow voids in aqueduct. Distinguish from atrophic ventriculomegaly of aging (which shows commensurate cortical atrophy).
Diagnostic workup: after suggestive history and imaging, large-volume lumbar puncture (LP) with 30-50 mL CSF removal is often performed to predict shunt response. Pre- and post-procedure gait assessment (timed up-and-go, gait video, cognitive testing). Improvement after LP predicts shunt response. Some centers use external lumbar drainage for several days for more definitive prediction.
Treatment: ventriculoperitoneal shunt. Neurosurgical placement of a shunt diverting CSF from ventricles to peritoneum. Gait often improves dramatically — sometimes within days. Cognition more variable. Urinary symptoms intermediate. Complications include shunt infection, malfunction, subdural hematomas. Patient selection matters — patients with concurrent significant cerebrovascular disease or Alzheimer's pathology benefit less.
The treatable mimic worth not missing: a patient with progressive gait, urinary incontinence, and mild cognitive decline who is diagnosed with "general dementia" and not worked up for NPH may have years of preventable progression. The shunt is not curative for all patients but is reasonably effective in well-selected cases.
When you encounter an older adult with a "magnetic" gait disproportionate to memory loss, particularly with urinary symptoms, the workup for NPH is appropriate. MRI, LP-with-gait-assessment, neurosurgery referral if confirmed. The treatable mimic deserves attention.