Freddi Segal-Gidan is Director of the Rancho Los Amigos/University of Southern California (USC) Alzheimer’s Disease Center and Assistant Clinical Professor in the departments of Neurology and Family Medicine at Keck School of Medicine, USC, and in Gerontology at L. Davis School of Gerontology at USC, Los Angeles.
DIAGNOSIS The diagnosis of iNPH is based on clinical findings. Making the diagnosis can be challenging, as the symptoms overlap with common age-related changes and age-associated medical conditions, and there is no single diagnostic test. A high index of clinical suspicion or an incidental finding on neuroimaging done in the diagnostic work-up for cognitive impairment/dementia (or some other reason) are the usual triggers for further investigation.
Clinicians should include iNPH in the differential, along with alternative diagnoses, when the history includes one or more of the three symptoms of iNPH: cognitive decline, gait disturbance, and/or urinary incontinence (see Table 1). While superficially appearing to be an easily recognizable condition, iNPH is actually a very complex disease that goes unrecognized and undiagnosed in many individuals.8 Evidence-based guidelines developed in 2005 attempted to devise a classification system based upon age, gait speed, nature of symptoms, neuroimaging changes, and CSF opening pressures.9
The symptoms of iNPH typically develop insidiously and progress slowly. The earliest symptom is most often gait disturbance. The gait disturbance associated with iNPH is described as “magnetic” or gait apraxia and includes trouble with initiation, reduced stride length, and a slow, cautious quality.10 Cognitive impairment typically has a frontosubcortical pattern, with psychomotor slowing, decreased attention or concentration, and problems with verbal fluency and executive function.11 Deficits in visuospatial and construction skills may also be observed.
Memory decline, which predominates in Alzheimer disease, may be less pronounced in iNPH. Urinary incontinence is usually a combination of urgency and frequency, mostly due to detrusor overactivity.12 A majority of patients (62%) treated for iNPH have all three symptoms of the triad, but in some cases only one or two symptoms are present.13 Gait disturbance is the most common feature, present in 98% of cases, followed by urinary incontinence (79%) and cognitive impairment (78%).13
Physical examination should include a complete neurologic exam. Mental status testing will typically show slowing, with decreased comprehension and increased time required to complete tasks. Decreased short-term memory recall may be improved with cues. Speech may be slow but is without aphasia or dysarthria. The gait pattern often includes a wide stance; slow, small steps with decreased floor clearance; and retained arm swing. Motor examination of the lower extremities may demonstrate some increased tone and slightly brisk reflexes.
