Sensory ataxia associated with vitamin B12 deficiency and hypocalcaemia in a patient with 'hikikomori' syndrome.

A man in his 40s presented with progressive gait instability and distal sensory disturbance after 2 years of 'hikikomori' syndrome associated with a depressive state. Neurological examination demonstrated severe sensory ataxia with sensory-dominant polyneuropathy. Serum vitamin B12 was markedly reduced (56 pg/mL), accompanied by elevated homocysteine levels (19.1 nmol/mL). Evaluation of calcium metabolism demonstrated hypocalcaemia due to vitamin D deficiency with secondary hyperparathyroidism. Sunlight exposure combined with methylcobalamin treatment improved both neurological symptoms and serum calcium levels. Repeated measurements during 4 years of follow-up demonstrated a strong positive association between serum vitamin B12 and corrected calcium levels. This case suggests that prolonged social withdrawal and reduced sunlight exposure may contribute to concurrent vitamin D and vitamin B12 deficiencies and that resultant hypocalcaemia may contribute to vitamin B12 deficiency.