THE AGE AT ONSET OF ALZHEIMERS-DISEASE AND AN INTRACRANIAL AREA MEASUREMENT - A RELATIONSHIP

Objective: To examine the possibility that premorbid brain size may in fluence the age at onset of symptoms of Alzheimer's disease (AD). Desi gn: Retrospective case series. Setting: Outpatients attending a memory disorders clinic in a tertiary referral center. Patients: Twenty-eigh t female patients with the diagnosis of probable AD, selected for the availability of informant derived estimates of age at onset of symptom s and computed tomographic scans of the head satisfying angulation cri teria. Main Outcome Measure: An average intracranial area of two adjac ent computed tomographic scan sections appropriately angled was used a s a correlate of premorbid brain size. Strict intracranial volume meas urement was not performed. Results: Age at onset of symptoms of AD cor related positively (r=.48, P=.009) with our measure of premorbid brain size. There was no confounding by education, height, or ethnicity. Co nclusion: Premorbid brain size may be an important determinant of the age at onset of symptoms of AD. Epidemiologic studies of AD may need t o assess the relationship between brain size and putative risk factors , eg, low educational attainment, since there is evidence that brain s ize is not distributed uniformly across populations.