Background Vitamin B12 is found in food of animal origin. Vitamin B12 deficiency leads to megaloblastic anaemia. It could be due to intrinsic factor deficiency or selective B12 malabsorption. In addition to anaemia, neurological symptoms (developmental delay, tremor, ataxia, irritability) may be seen in B12 deficiency.

Case A previously healthy 1 year 4-months-old girl, who was born after a normal full term pregnancy, with a normal developmental history until 1 year 2 months of age, presented to the hospital with somnolence, choreic and some intermittent myoclonic movements, and a regression of her psychomotor skills starting 2 months ago. The baby was exclusively breastfed, with normal growth curves. Upon admission, she showed a significant delay in her developmental milestones, a neurologic regression with somnolence, and some intermittent myoclonic movements. Laboratory studies showed the presence of an isolated mild macrocytic anaemia with abnormal hemolytic markers (high LDH, low haptoglobin). Otherwise, normal CBC, glycemia, electrolytes, pyruvic acid and lactate, liver, renal and thyroid function tests. Magnetic resonance imaging of the brain showed the absence of significant abnormalities, and the EEG showed the presence of an intermittent low amplitude signal in the frontal region. Further investigations showed the presence of an isolated vitamin B12 deficiency (52.72 pg/ml, normal value 191–663 pg/ml) with a normal serum folate level. The child was treated with intramuscular vitamin B12 injections, starting with a dose of 0.2mcg/kg/day for 2 days. And since, neurological symptoms improved directly after starting therapy. On day 6 after starting the vitamin B12 therapy, the child presented again to the hospital with increased nonstop myoclonic movements, despite a progressive recuperation of her psychomotor skills. New neurological symptoms were described in literature in some rare cases, where involuntary movements may be noticed during the treatment with vitamin B12. Furthermore, the side effects of the treatment should not be a contraindication to continue the vitamin B12 injections, or otherwise an irreversible regression of the neurological status may occur as described in the literature. The treatment should be started more progressively to avoid or decrease its side effects.