May 2nd 2005When Gordon R. Kelley, MD, was called to the ICU in Kansas City, Mo, to evaluate a deteriorating patient who had apparently overdosed on methadone, he was puzzled. CT and MRI scans revealed an obstructive hydrocephalus associated with abnormal signals throughout the cerebellum, basal ganglia, and hippocampi. He knew that these findings were not consistent with a typical cerebrovascular injury, but he and other treating physicians were unsure of the cause of the findings. Reaching for his handheld computer, he entered several key words into his favorite program, NERVLINE: cerebellum . . . heroin . . . leukoencephalopathy