Diagnosing Alzheimer's disease in elderly, mildly demented patients: the impact of routine single photon emission computed tomography

Based on the observation of bilateral temporoparietal hypoperfusion in Alzheimer's disease (AD), single photon emission computed tomography (SPECT) is advocated by some as a powerful diagnostic tool in the evaluation of demented patients. We studied whether routine brain SPECT in elderly, mildly demented outpatients increases the a priori diagnostic sensitivity and specificity of a careful clinical examination.99mTc-HMPAO SPECT imaging was performed in 110 patients for a first evaluation for dementia. A semiquantitative measure of temporoparietal (TP) perfusion was calculated as the ratio of the activity in the temporoparietal cortex to activity in the cerebellum. A diagnosis of probable AD according to the McKhann criteria was made in 68 patients (mean age of 79.3 years) based on the results of a clinical examination, ancillary investigations and a 6-month follow-up. TP perfusion was significantly lower in AD patients than in 18 age-matched, non-demented controls. However, at a specificity of 89%, sensitivity was only 43% for detecting probable AD. The clinicians judged that SPECT had contributed to the final diagnosis in only 8% of the demented patients investigated. Routine brain SPECT in elderly, mildly demented outpatients does not contribute substantially to diagnostic accuracy after a careful clinical examination using current diagnostic criteria. Clinical guidelines have to be developed for the use of SPECT in patients with (suspected) dementia.