To the Editor. —We would like to comment on the article by Johnson et al 1 that appeared in the April 1988 issue of theArchives. 1 The authors reported that single photon emission computed tomography (SPECT) brain imaging with iofetamine hydrochloride I 123 was able to reflect dementia severity in patients with Alzheimer's disease (AD). To determine dementia severity, they used a global estimate of functional disability on a 4-point scale. Dividing a group of patients with AD into several groups based on functional impairment seems rather artificial. The great range of overlap in score on the Blessed Dementia Scale 2 between the four groups (Table 1 in the article) seems to support this. In our opinion, a comparison of the whole spectrum of dementia should be made with SPECT abnormalities. Further-more, dementia severity was determined by estimating functional disability, without referring to previous ability. We think that the