Olfactory ability in normal pressure hydrocephalus as compared to Alzheimer's disease and healthy controls

Normal pressure hydrocephalus (NPH) is a treatable neurological disorder that appears in older adults, lacks specific diagnostic criteria, and resembles symptoms seen in Alzheimer's disease (AD). Presently, differentiating NPH from AD in the early stages of symptom presentation remains difficult. This study established whether olfactory testing may be useful in this regard. In addition, we determined whether olfactory function of NPH patients differed before and after extended lumbar drainage (ELD), as well as six months after surgical implantation of a ventriculoperitoneal (VP) shunt.

Twenty-two NPH patients (mean age=77.6yrs), 14 age- and gender-matched healthy controls (mean age=79.9yrs), and 7 AD patients (mean age=75.5yrs) were administered the 40-item University of Pennsylvania Smell Identification Test (UPSIT). Eighteen of the 22 NPH patients were also tested following ELD and 8 patients were tested six months following implantation of VP shunt.

Prior to ELD, patients with NPH scored significantly higher on the UPSIT than those with AD [respective means (SDs)=26.9 (7.1) & 14.1 (4.7)]. While the mean NPH score was significantly below that of the matched controls [control mean (SD)=32.7 (6.7)], their test scores were nonetheless within the general normal range, as determined from published normative data (48th percentile). The UPSIT scores did not differ significantly among the three longitudinal time points in the NPH patients.

Olfactory testing may be useful in differentiating between patients with NPH and patients with AD. Odor identification test scores of NPH patients are not influenced by the release of intracranial pressure via ELD or six months following implantation of a VP shunt.