Myths about vitamin B12 deficiency.

Neurologic manifestations of vitamin B12 deficiency are protean, including neuropathy, depression, and dementia. We present evidence to dispel confounding myths about vitamin B12 deficiency. Hematologic indices are normal in up to 30% of patients with vitamin B12 deficiency, and results of the Schilling test may be normal in patients with symptoms of deficiency. Isolated neuropathy or myelopathy may occur independently, but often appear concurrently. The neuropathy is primarily axonal and predominantly sensory. Myelopathy is caused by demyelinated areas in posterior and lateral columns. After therapy, recovery from neuropathy is incomplete or may extend for several years. Vitamin B12 replacement should not be withheld from patients with borderline vitamin B12 levels, since the consequences of allowing myelopathy, neuropathy, dementia, and mental disorders to worsen clearly outweigh any disadvantage of therapy.