Pupil-sparing, painless compression of the oculomotor nerve by expanding basilar artery aneurysm: A case of ocular pseudomyasthenia

Background: Oculomotor nerve paresis may have relatively benign but also life-threatening causes. Distinguishing between these is of great clinical importance. Objective: To reveal a potential pitfall of the clinical evaluation of oculomotor nerve paresis. Patient: Single case observation. Results: A 56-year-old man had fluctuating diplopia and fatigable ptosis, promptly relieved by intravenous edrophonium, leading to the diagnosis of ocular myasthenia gravis. His pupillary function was intact. A few days after the initial diagnosis, he suffered a subarachnoid hemorrhage secondary to the rupture of a basilar artery aneurysm. His ocular symptoms were related to aneurysmal oculomotor nerve compression. Conclusion: Patients with oculomotor nerve dysfunction need more detailed evaluation because the underlying cause cannot be safely determined on a clinical basis.