Fuld's formula and WAIS subtests in differential diagnosis of dementia

The Fuld formula and the linear discriminant function applied to WAIS subtest scores were tested for their ability to identify Alzheimer's disease and senile dementia of the Alzheimer type in a group of 101 demented subjects. The sensitivity and specificity of Fuld's formula for Alzheimer dementia against other dementias were 44.2% and 73.8% respectively; when compared with an age-matched normal control group specificity was 91.4%. When the linear discriminant function was applied only WAIS subtest scores in "similarities and digit span" and "object assembly" significantly differentiated Alzheimer from other dementias (sensitivity 61.5% and specificity 63.3%). Specificity increased to 97.1% when the function was applied to discriminate Alzheimer from normal controls. Discriminant analysis applied to other WAIS subtests for the two demented groups revealed "picture completion" as significantly differentiating the groups but it did not contribute to diagnostic accuracy. WAIS scores are of limited value in the differential diagnosis of dementias.