[Subdural block which appeared 21 days after beginning continuous epidural block].

An epidural catheter was inserted at the T10-11 interspace for the treatment of acute herpetic pain in a 68-year-old woman. Loss of resistance method with saline was used for identifying the epidural space. After negative aspiration test for cerebrospinal fluid and blood, continuous epidural infusion of 0.2% ropivacaine 2 ml x hr(-1) with intermittent injections of 1% mepivacaine 3 ml was performed for 20 days without side effects. However, on the 21st day, Horner's syndrome and weakness of the left arm and leg appeared 10 minutes after injection of 1% mepivacaine 3 ml. The symptoms and signs suggested subdural block. Migration of the epidural catheter into the subdural space may have occurred. Subdural block may occur even if the catheter is initially properly placed in the epidural space.