Summary: Encephalopathy associated with B12 deficiency improves with treatment if initiated early; however, the features of mental impairment as well as the rate and pattern of improvement with vitamin replacement remain unclear. A patient with marked B12 deficiency syndrome is presented with neurological, neuropsychological, neuropsychiatric, and neurophysiological examinations before and 2 weeks and 3 months after treatment was initiated. The initial pattern of encephalopathy was consistent with subcortical dementia. With vitamin replacement, psychomotor speed, mood, copying skills, and frontal system functions quickly improved but performance on memory, block design, and a visuoperceptual task remained impaired.
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