HMPAO (CERETEC) SPECT BRAIN-SCANNING IN THE DIAGNOSIS OF ALZHEIMERS-DISEASE

OBJECTIVE: To evaluate the accuracy of Single Photon Emission Computed Tomography (SPECT) scanning in the diagnosis of Alzheimer's Disease ( AD) and its capacity to improve the diagnostic accuracy of conventiona l clinical evaluation. DESIGN: Comparison of SPECT scanning of AD and normal subjects with the criterion standard of clinical diagnosis conf irmed by 1-year repeated evaluation. SETTING: A memory clinic in a ter tiary care university hospital. PATIENTS: One hundred twenty patients were evaluated upon entering the Jewish General Hospital (McGill Unive rsity) Memory Clinic. Fifty-eight patients were diagnosed as having AD and 17 as having vascular dementia. Twenty unmatched controls (recrui ted mainly through newspaper advertisements) were normal, and 25 had c ognitive impairment without dementia (not included in the statistical analysis). MAIN OUTCOME MEASURES: Comparison of visual inspection of S PECT, based on the system of classification developed by Holman et al. , using B pattern alone as positive or B (bilateral posterior temporal and/or parietal cortex deficits) or C (bilateral posterior temporal a nd/or parietal deficits with additional defects) pattern and B or C or D (unilateral posterior temporal and/or parietal defects with or with out additional defects) as positive compared with clinical diagnosis a fter repeated evaluations. Sensitivity and specificity, as well as pos itive predictive value (PPV) and negative predictive value (NPV) based on the prevalence of AD in a memory clinic setting of 30% or 50%, wer e calculated.RESULTS: With B pattern as positive, the sensitivity of S PECT was 21% whereas the specificity was 80%. With B or C as positive, the sensitivity was 29% and the specificity was 75%. With B or C or D as positive, the sensitivity was 55% and the specificity was 65%. Wit h a 30% prevalence, the PPV with B pattern as positive was 31% whereas the NPV was 30%. The PPV with B or C as positive was 33% while the NP V was 29%, and the PPV with B or C or D as positive was 40% whereas th e NPV was 23%. With a 50% prevalence, the PPV with B pattern as positi ve was 51% and the NPV 49.6%; the PPV with B or C as positive was 54% and the NPV 48.6%; the PPV with B or C or D as positive was 61% while NPV was 41%. CONCLUSION: The sensitivity and specificity were too low for SPECT to be useful as a diagnostic test for AD. The poor positive and negative predictive values in our tertiary care clinic mean that S PECT is not useful in ''ruling-in'' or ''ruling-out'' AD in that setti ng. In fact, clinical evaluation is more accurate.