Brain in toxic encephalopathy. FLAIR magnetic resonance imaging (MRI) scan of an axial section through the brain of a 44-old transplant patient in a coma due to toxic encephalopathy caused by treatment with cyclosporin. Toxic encephalopathy is a degenerative neurologic disorder caused by exposure to toxic substances. Cyclosporin is a common immunosuppressant used in organ transplantation to prevent rejection. Some adverse effects of cyclosporin, such as hepatic (liver) and renal (kidney) toxicity, are relatively common, however central nervous system toxicity caused by cyclosporin is rare.