Caudal paramedian midbrain syndrome

BACKGROUND: Caudal midbrain lesions involving the entire decussation of the superior cerebellar peduncles have a distinctive clinical picture: bilateral cerebellar ataxia, eye-movement disorders, and palatal myoclonus. Occasionally, unilateral lesions may produce a similar neurologic picture. OBJECTIVE: To define the clinical and radiologic picture of patients with unilateral lower midbrain ischemic lesions of the decussation of the brachium conjunctivum. METHODS: Five patients with MRI evidence of unilateral paramedian caudal midbrain infarction were investigated, after the acute stage. RESULTS: All patients had bilateral cerebellar dysfunction characterized by dysarthric speech, truncal and gait ataxia, and dysmetric movements of the limbs, which were more pronounced on one side. Ocular movement abnormalities were observed in three cases. A constant MRI finding was a bilateral inferior olivary degeneration, but only one patient displayed a delayed palatal tremor. CONCLUSIONS: A single strategically placed unilateral lesion can cause bilateral dysfunction. In addition, a bilateral cerebellar syndrome can occur with unilateral lesions in the lower midbrain with a wide range of other clinical features.