Effect of fluoxetine on regional cerebral metabolism in autistic spectrum disorders: a pilot study

The regional metabolic effects of fluoxetine were examined in patients with autism spectrum disorders. Six adult patients with DSM-IV and Autism Diagn ostic Interview (ADI) diagnoses of autism (n = 5) and Asperge's syndrome (n = 1), entered a 16-wk placebo-controlled cross-over trial of fluoxetine. T he patients received F-18-deoxyglucose positron emission tomography with co -registered magnetic resonance imaging at baseline and at the end of the pe riod of fluoxetine administration. After treatment, the patients showed sig nificant improvement on the scores of the Yale-Brown Obsessive-Compulsive S cale - Obsessions subscale and the Hamilton Anxiety Scale; Clinical Global Impressions - Autism scores showed 3 of the patients much improved and 3 un changed. Relative metabolic rates were significantly higher in the right fr ontal lobe following fluoxetine, especially in the anterior cingulate gyrus and the orbitofrontal cortex. Patients with higher metabolic rates in the medial frontal region and anterior cingulate when unmedicated were more lik ely to respond favourably to fluoxetine. These results are consistent with those in depression indicating that higher cingulate gyrus metabolic rates at baseline predict SRI response.