Involuntary movement in infants during vitamin B12 treatment.

Megaloblastic anemia is rare in infants and is generally due to vitamin B12 (cobalamin) deficiency in the mother. Neurologic symptoms of vitamin B12 deficiency include irritability, failure to thrive, hypotonia, and developmental regression/delay. Herein we present 2 infants with vitamin B12 that developed movement disorder 5 d after initiation of vitamin B12 treatment. Symptoms included tremor and myoclonus, involving in particular the face, tongue, and hands. Clinical findings in infants associated with vitamin B12 deficiency vary, and temporary involuntary movement can be observed during vitamin B12 therapy.