Divergence Paralysis Caused by Acute Midbrain Infarction

A 41-year-old woman with idiopathic thrombocytopenic purpura and dyslipidemia abruptly developed vertigo, truncal ataxia and divergence paralysis. Cranial magnetic resonance imaging demonstrated the presence of infarction in the left superior paramedian mesencephalic artery involving the vicinity of the periaqueductal gray matter. The symptoms rapidly resolved under the administration of anti-platelet agents. The precise location of the hypothetical divergence center of the ocular motor system remains unclear because the lesions responsible for divergence paralysis are rarely identified on neuroimaging. We emphasize that this is a first reported case of DP caused by acute midbrain infarction and speculate that the mesencephalic reticular formation may be partially involved.