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Vitamin B12 deficiency is known to cause widespread neurological and psychiatric manifestations usually attributed to abnormal myelin synthesis. 1 2 There are rare case reports of partially reversible leukoencephalopathy due to cyanocobalamin deficiency in the setting of very low serum B12 levels. 3-7 Autonomic dysfunction with orthostatic hypotension that responds to B12 supplementation, without evidence of other neurologic dysfunction, has also been reported. 8 We report the case of a 62-year-old woman with cognitive decline, autonomic dysfunction, progressive leukoencephalopathy, "normal" B12 , methylmalonic acid (MMA) and homocysteine (Hcys) levels, and positive anti-intrinsic factor antibodies who clinically and radiologically responded to B12 supplementation.
Case report
A previously healthy social worker experienced her first episode of depression at the age of 62. She was treated with a selective serotonin reuptake inhibitor after organic causes and structural brain abnormalities were ruled out. One year later, the patient developed syncopal episodes that were frequent enough to impair her ability to work. She felt dizzy in the standing position and was unable to hold her head up in the sitting position. Autonomic testing revealed severe sympathetic and parasympathetic failure. Supine blood pressure was 131/62 mm Hg with a heart rate of 61 beats per minute. Passive head-up tilt elicited a progressive fall in blood pressure, and after 12 min, blood pressure was 52/28 mm Hg. Despite the profound fall in blood pressure, heart rate only increased to 81 beats per minute. Heart rate variability during paced deep breathing was markedly reduced. Within 3 years the patient became bed-bound and was unable to stand because of severe orthostatic symptoms. She had minimal response to hydration, salt supplementation and treatment with mineralocorticoid (fludrocortisones) and [alpha]-agonist agents (midodrine). During this time the patient developed severe anorexia with a 30-lb weight loss and body mass index of 18. Her husband noticed worsening cognition with memory and concentration deficits. Examination during this time period found mini-mental status examination variably between 21 and 25/30, positive Myerson's sign, snout and palmomental reflexes, decreased vibration and joint position sense below the knees and a wide-based gait. Neuropsychological testing revealed a dementia rating scale of 122/144. Extensive testing over 4 years included blood counts, liver function tests, renal function tests, chest and abdominal scans...