MAR 05, 2013
The authors report the case of a 69-year-old man with new-onset isolated diplopia only in downward gaze. Hess chart findings revealed underactivity of the superior oblique (SO) and inferior rectus (IR) muscles of the right eye. Diffusion-weighted imaging revealed the presence of an acute infarction in the bilateral ventral midbrain suggesting involvement of the infranuclear oculomotor nerves. The oculomotor nuclei and rostral interstitial nucleus of the medial longitudinal fasciculus, the center of vertical gaze control, were spared. The authors conclude that their patient's symptoms reflected mild impairment of the IR and SO fascicles.
Ocular examination revealed normal pupil size and light reflexes. Neither limitation of extraocular movements nor ptosis was evident, and the patient's convergence was preserved.
The authors explain that partial fascicular oculomotor palsy includes various combinations of ocular muscle impairment that depend on even slight differences in midbrain lesions. Isolated IR palsy caused by midbrain infarction has been reported, suggesting the possible selective involvement of an individual fascicle.