Avellis syndrome due to borreliosis.

Avellis syndrome is a rare form of alternating hemiparesis that is usually because of atherosclerosis. We report a 67-year-old man who developed paresthesiae of the left arm, dysphagia and dysphonia. The clinical picture, magnetic resonance imaging and cerebrospinal fluid findings were consistent with Avellis syndrome caused by brain stem arteritis because of late stage Borrelia burgdorferi infection, an extremely unusual aetiology for Avellis syndrome; this may well be the first such instance. It may be unrecognized in elderly patients with other risk factors for cerebrovascular disease.