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A 62-year-old Caucasian woman with a 12-month history of progressive paresthesias below the first lumbar level (L1) was hospitalized for rapid onset of ascending sensory impairment to the sixth thoracic level (T6), ataxia, saddle anesthesia, and diminishing central vision. Best-corrected visual acuity (BCVA) was 20/40 in the right eye and 20/400 in the left eye. Her BCVA had been 20/25 bilaterally two years prior. Color discrimination was severely diminished at 4/12 Ishihara color plates in the right and 1/12 in the left. Dilated fundus exams showed small flat yellowish deposits limited to wellcircumscribed subfoveal areas of retinal pigment epithelium (RPE) atrophy (Figure 1). There was no optic nerve pallor. The fundus appearance and fluorescein angiogram findings were similar to those described in cases of congenital MMA. 4,5 Full-field electroretinograms revealed mildly reduced scotopic and photopic responses in the left eye.Despite a low normal level of vitamin B12 (298 pg/ml; reference 180-914 pg/ml), the patient's serum methylmalonic acid (0.30 mM/l; reference o0.30 mM/l) and homocysteine (22.2 mM/l; reference 6.2-15.0 mM/l) levels were elevated, consistent with a diagnosis of vitamin B12 deficiency. Furthermore, brain and spinal cord magnetic resonance imaging revealed T2-weighed hyperintensity of the entire dorsal columns, characteristic of vitamin B12 deficiency.The patient was treated with cyanocobalamin injections by the inpatient Neurology service. Six weeks after treatment, her ataxia, paresthesias, as well as bowel and bladder function improved. Color discrimination improved to 8/12 in the right and 5/12 in the left eye.

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