Myasthenia Gravis with Horizontal Gaze Palsy
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A 68-year-old male presented with complaints of sudden-onset lid ptosis and diplopia beginning 3 weeks ago. He denied any past medical history of hypertension or diabetes mellitus. His best-corrected visual acuity was 6/12 OD and 6/15 OS. Eye fissures were found to be 7.5 mm in the right and 6.5 mm in the left. A prism cover test revealed 3 prism diopters of esotropia on primary gaze, which increased to 16 prism diopters on left gaze. Extraocular movements showed moderate limitation on left gaze in both eyes (Fig. 37.1, Video 37.1). Slit lamp examination showed a moderate degree of nuclear sclerosis in both lenses. Fundoscopic examination was normal. A neostigmine test was borderline positive with partial resolution of the gaze palsy at 40 min (Fig. 37.2). MR angiography of the brain demonstrated minimal bilateral stenosis of the distal internal carotid arteries. A peripheral blood examination was ordered, and positive anti-acetylcholine antibody was found (9.02 nmol/L). The patient’s ptosis and diplopia condition improved after the use of Mestinon and prednisolone for 2 weeks (Fig. 37.3). However, he began to occasionally experience dysphagia, easy choking, and chest tightness. An MR imaging of the chest revealed a 3.6 × 1.8 × 5.9 cm mass lesion at the anterior mediastinum, suspected to be thymoma (Fig. 37.4). Surgical removal of the thymoma was done 2 months after onset and pathological report indicated encapsulated thymoma.
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