Clinical Reasoning: A 75-year-old woman with visual disturbances and unilateral ataxia

Abstract

A 75-year-old woman presented in July 2007 with 2 months of oscillopsia when looking downward and horizontal diplopia during rapid rightward gaze. She reported 3 weeks of progressive clumsiness of the right limbs, weakness of the right leg, and an unsteady gait. She denied cognitive dysfunction, headache, bulbar or sensory symptoms, muscle stiffness/spasms, antecedent infection, fever, or other systemic complaints. Nine years earlier, the patient had experienced an episode of diplopia and unsteadiness which resolved spontaneously after 3 months. Her neurologic examination in 1998 had revealed downbeat nystagmus, a right internuclear ophthalmoparesis (INO), and gait ataxia. Brain MRI and stroke evaluation had been negative. Type I diabetes mellitus was diagnosed several months after this initial episode. In the 1980s, a low vitamin B12 level (value unknown) was thought to have been an incidental finding; levels >500 ng/L have been maintained with a B12 supplement. There was also a history of well-controlled hypertension. A grandparent had type I diabetes, but no relatives had neurologic disorders. She rarely consumed alcohol and never used tobacco or recreational drugs. General medical examination had normal results, including the absence of vitiligo. Mental status examination was unremarkable with clear speech. Funduscopic, pupillary, visual field, and monocular acuity examinations were unremarkable. Near card straight-ahead binocular acuity was 20/20, but only 20/50 in lateral downgaze due to oscillopsia. The eye movement abnormalities were saccadic pursuit, gaze-evoked nystagmus, downbeating nystagmus maximal on lateral downgaze, and saccadic slowing but full range of the left adducting eye (i.e., left INO) (see videos 1, 2a, and 2b on the Neurology ® Web site at www.neurology.org). Convergence was normal. There was no rigidity or stiffness of limb or axial muscles. There was 4+/5 right leg weakness (hip/knee flexors, toe extensors), with hyperreflexia, downgoing plantar responses, and normal sensation. There was right-sided …