The treatment of vitamin B12 deficiency caused severe neurological complications in an infant.

A report describes a case of a 10-month-old boy with pathological neurological symptoms of muscle tremors of the upper limbs, head, tongue, and lips, as well as delayed psychomotor development and decreased muscle tone. 

The parents described no significant pre or post-natal history, except when the child was three months old- they observed a decreased muscle tone; around the age of 6 months- a decrease in appetite, and at nine months of age- due to delayed psychomotor development and decreased muscle tone, he received a hospitalization. 

The patient could not sit, pull himself up to sit, or crawl. He could not hold his head stable when lying on his stomach. Laboratory investigation revealed megaloblastic anemia, decreased B12 concentration, abnormal tandem mass spectrometry (MS/ MS) results (reduced amino acid concentration of methionine and free carnitine), and markedly elevated methylmalonic acid (MMA) concentration.

 The slightly widened cerebral ventricles on brain ultrasound prompted an MRI scan that revealed dilatation of the parieto-cerebral spaces with wide Sylvian furrows, widened ventricular system, and frontal horns of the lateral ventricles. Dilation of Extracerebral and intracerebral fluid spaces suggested atrophic brain. Encephalopathic electroencephalography (EEG) revealed abnormal basal activity, while a video-EEG study did not document any seizure-like incidents. 

The patient received 1 unit of red blood cell concentrate supplementation and two doses of vitamin B12, 100 μg each, administered by intramuscular injection on two consecutive days, after which he received a discharge. However, later that day, the child demonstrated tremors in his upper limbs, head, tongue, and mouth and reached the nearest hospital. His laboratory tests revealed significantly elevated serum vitamin B12 levels (5570 pg/mL), hyper-transaminasemia, and elevated lactate dehydrogenase. The patient received anticonvulsant treatment (diazepam, clonazepam, chlorpromazine, and midazolam), but it brought no clinical improvement, which raised the suspicion of an inborn error in metabolism.

The mother's vitamin B12 concentration was normal, but from the sixth month of the child's life, she received vitamin B12 supplements. Considering the laboratory and clinical findings, the clinicians suspected tremors caused by vitamin B12 supplementation in severe deficiency. The patient received clonazepam (target dose of 0.1 mg/kg/day) and showed a reduction in tremors from the fifth day of full-dose therapy. On the ninth day of full-dose treatment, he showed only minimal tongue, head, and upper extremities tremors. He continued the therapy and then gradually reduced it until complete withdrawal. Two months following the treatment, the patient showed complete disappearance of muscle tremors. 

Even though the patient underwent regular physiotherapy and his vitamin B12 levels returned to normal, he still experienced delayed psychomotor development and had significantly reduced muscle tone. The molecular investigation detected a change in the SLC9A7 gene, variant: c.203G>A(p.Arg68Gln). At 22 months of age, the boy continues to gain weight properly, can sit up independently, crawl, and walks with support, shows interest in toys, and pronounces single words. He continues to be under care and is receiving intensive somatosensory physiotherapy.

Leśniak A, Patalan M, Sieńko M. et al. Severe neurological complications in an infant during vitamin B12 deficiency treatment: a case report. Pomeranian J Life Sci 2023;69(1):53-57 doi: 10.21164/pomjlifesci.913