Incidence and causes of nondegenerative nonvascular dementia: A population-based study

Background: Information on the incidence of nondegenerative and nonvascular dementia is limited. Design: We used the records-linkage system of the Rochester Epidemiology Project to ascertain incident cases of dementia in Rochester, Minn, from January 1, 1990, through December 31, 1994. To define causes of dementia, we reviewed all diagnoses, imaging study results, laboratory test results, and clinical courses, as recorded historically in the patient dossier. Results: We found 560 incident cases of dementia, and 60 of them (10.7%) had onset before the age of 70 years (younger-onset group). Forty-three cases (7.7%) were due to nondegenerative nonvascular causes and represented 30.0% of the total in the younger-onset group, but only 5.0% of the total in the older-onset group (aged 70-99 years). The most common nondegenerative nonvascular causes were cancer with or without brain metastases (n=13), chronic alcoholism (n=7), and chronic mental illness (n=11). There were no cases of dementia due to normal-pressure hydrocephalus, subdural hematoma, hypothyroidism, vitamin B12 deficiency, or neurosyphilis. There were 2 individuals with acute confusion due to subdural hematoma and 1 with hypothyroidism whose cognition normalized with therapy. Conclusions: Nondegenerative nonvascular causes were more common than expected in patients with a younger onset of dementia. None of the patients with dementia reverted to normal with treatment of the putative reversible cause.