SPECT in Alzheimer's disease: features associated with bilateral parietotemporal hypoperfusion.

OBJECTIVE: To investigate why bilateral parietotemporal hypoperfusion, the typical SPECT pattern of Alzheimer's disease (AD), occurs in some but not in all patients with probable AD. METHODS: We reviewed the SPECT scans of 220 patients presenting with cognitive impairment. Among them, 104 patients fulfilled NINCDS-ADRDA criteria for probable AD, 48 (32 women) with early onset (before age of 65) and 56 (40 women) with late onset of the symptoms. Dementia severity was assessed by the Mini-Mental State Examination. The SPECT scans were classified by visual inspection blind to clinical diagnoses. RESULTS: Bilateral parietotemporal hypoperfusion was more frequent in patients with severe AD, in those with early onset of the symptoms, and in men. Duration of symptoms, type of gamma-camera or radiopharmaceutical agent used were not associated with this SPECT pattern. CONCLUSION: These findings may be useful in the clinical setting and point to heterogeneity of AD according to age at onset.