Isolated pupil-sparing third-nerve palsy as the presenting sign of multiple sclerosis

A 27-year-old man presented with an isolated, pupil-sparing, partial third-nerve palsy. Etiologic investigations proved unrevealing. Subsequent development of an optic neuropathy prompted magnetic resonance imaging, which confirmed the clinical suspicion of multiple sclerosis. Rarely does multiple sclerosis present with oculomotor nerve involvement.