Tonic seizures are a poorly understood manifestation of demyelinating
disease, first reported in 4 patients with multiple sclerosis. We describe a patient with tonic extension of the left limbs caused by a right-sided brainstem lesion as the first manifestation of demyelinating
disease. A 19-year-old man was referred with a 4-month history of spontaneous attacks of mild paresthesias of the left arm and leg, followed by 15-45 s of rigid extension of the left limbs, occurring up to 25 times per day. Two months after onset, an MRI scan revealed areas of T2 abnormality in the lateral right cerebral peduncle and deep frontal white matter. The EEG was normal, including during hyperventilation which induced a typical episode. All attacks were successfully suppressed by carbamazepine, phenytoin, and valproate monotherapy. Serologic testing for toxoplasmosis, cytomegalovirus, Epstein-Barr virus,
Lyme disease, and HIV was negative. Cerebrospinal fluid oligoclonal bands were absent but cerebrospinal fluid immunoglobulin G was mildly elevated (4.2 mg/dl). Over the next 30 months, serial MRIs revealed a normal spinal cord and persistence of the midbrain lesion, with resolution of some of the white matter lesions but reappearance of others. At 46 months, the midbrain lesion resolved on MRI, and the spasms no longer occurred spontaneously, nor could they be elicited by hyperventilation. While two previous reports have shown internal capsule lesions to underlie the tonic spasms in demyelinating
disease, this is the first report in which a brainstem lesion has been causative.