Severe neurological complications in an infant during vitamin B₁₂ deficiency treatment: a case report

Disorders of vitamin B₁₂ (cobalamin) metabolism in children can be manifested by numerous symptoms. They result from the dysfunction of many systems, including the central nervous system. The most common cause of cobalamin deficiency in infants is inadequate supplementation of the vitamin with food. This mainly affects children who are exclusively breastfed by mothers who follow a diet with insufficient supplementation of vitamin B₁₂, including an imbalanced vegetarian or vegan diet. Adequate vitamin B₁₂ supplementation is essential for the proper growth and development of a child. However, attempts to compensate for severe vitamin B₁₂ deficiency can paradoxically lead to severe adverse reactions to vitamin B₁₂ treatment.

In this paper, we present a case of a 10-month-old boy with global developmental delay, muscle hypotonia, and profound vitamin B12 deficiency with megaloblastic anemia. The boy developed pathological neurological signs after intramuscular injections of vitamin B₁₂. The symptoms included muscle tremors of the upper extremities, head, tongue, and lips. A broad differential diagnosis including inborn errors of metabolism and other genetic disorders is discussed. We describe treatment that led to the complete resolution of symptoms related to the side effects of the B₁₂ therapy. The patient’s psychomotor development during over 1 year of clinical follow-up is also analyzed.