Decreased computerized tomography numbers in patients with presenile dementia. Detection in patients with otherwise normal scans.

Patients in their 50s who show clinical signs of dementia (possible Alzheimer's disease) often have ocmputerized tomographic (CT) scans that appear normal. This study examined the mean CT number within a 169-pixel sample in white matter in the centrum semiovale slice. Slice sizes ranged from 6,800 to 9,000 pixels; all were without contrast enhancement. The CT numbers were higher for six nondementia cases (CT numbers of 41 and above)than for 14 dementia cases (CT numbers of 40 and below). The non-overlap in mean CT numbers between the two groups was observed independent of the presence or absence of prominent sulci. Similar low CT numbers were observed for seven patients with senile dementia. Differential diagnosis between dementia and depression may be better aided by studying the CT numbers rather than the presence of prominent sulci.