Localization of level of lesions in internuclear ophthalmoplegia through assessment of masseter and blink reflex

The masseter and blink reflexes were investigated in 100 patients with internuclear ophthalmoplegia due to multiple sclerosis (58 patients) or lacunar brainstem infarction (42 patients). In unilateral internuclear ophthalmoplegia, 38 of 60 patients (63.3%) had masseter reflex abnormalities, two patients (3.3%) showed changes of the blink reflex R1 component, and 13 patients (21.7%) combined alterations of the masseter reflex and the blink reflex R1 component. 46 (86.8%) of these 53 patients with electrophysiological abnormalities had unilateral changes, which were ipsilateral to the medial longitudinal fasciculus lesion in 42 patients (91.3%). In bilateral internuclear ophthalmoplegia, 24 of 40 patients (60.0%) had abnormalities of the masseter reflex, two (5.0%) showed changes of the blink reflex R1, and nine (22.5%) combined alterations of the masseter reflex and the blink reflex R1 component. 20 (57.1%) of these 35 patients with electrophysiological abnormalities had bilateral changes. Thus, masseter reflex abnormalities indicating midbrain lesions were seen in 63.3% and 60.0%, respectively, of unilateral and bilateral internuclear ophthalmoplegia. Blink reflex R1 component changes with or without impairment of the masseter reflex indicating rostral pontine to midpontine lesions occurred in 25.0% and 27.5%, respectively. These figures correspond to the results of postmortem examinations and to theoretical considerations based on the length of the medial longitudinal fasciculus.