Recurrent encephalopathy associated with pegylated beta-interferon treatment.

A 62-year-old woman with a history of multiple sclerosis (MS) presented with recurrent episodes of confusion, dysarthria and gait difficulties. These episodes occurred about 3 days after administration of pegylated interferon-beta-1a (Plegridy®) and resolved spontaneously in around 4 days. The brain MRI scan, laboratory findings and cerebrospinal fluid analysis during these episodes were negative for other causes of encephalopathy. She discontinued treatment with interferon and was started on teriflunomide, experiencing no recurrence of symptoms. We believe that interferon was responsible for this patient's recurrent encephalopathic syndrome, possibly due to its effects on inflammatory cytokines and endothelial dysfunction.