Isolated superior oblique palsies with electrophysiologically documented brainstem lesions

Over a 13.5-year period, we observed 10 patients with isolated superior obl ique palsies in whom electrophysiological abnormalities indicated brainstem lesions. In 7 patients unilateral masseter reflex abnormalities were seen, and were located on the side of the superior oblique palsy in 2 patients a nd on the opposite side in 5 patients. Two patients had slowed gain of foll owing eye movements to the side contralateral to the superior oblique palsy , Slowed adduction saccades in the eye contralateral to the superior obliqu e palsy were seen in 1 patient. Clinical improvement was frequently tin 7 o f 10 patients) associated with improvement or normalization of electrophysi ologic findings. Magnetic resonance imaging (MRI) was normal, showing no ev idence of brainstem lesions in 6 patients. Unilateral superior oblique pals y may be the only clinical sign of a brainstem lesion. Although such a caus e may be underdiagnosed if based on MRI-documented lesions only, it remains a rare condition. (C) 2000 John Wiley & Sons, Inc.