A Case of Hypocalcaemia Due to Vitamin D Deficiency in ‘Hikikomori’ Syndrome

Objective: To describe hypocalcaemia due to vitamin D deficiency in ‘hikikomori’ syndrome. Materials and methods: A 37-year-old man with ‘hikikomori’ syndrome for a year was admitted with hypocalcaemia (serum ionic calcium 1.17 mmol/l). Serum 1,25(OH)2-vitamin D3 determined by liquid chromatography–tandem mass spectrometry was depressed at 12.1 pg/ml (29.0 pmol/l) and plasma intact PTH elevated at 324 ng/l. Administration of 1 μg/day 1α(OH)-vitamin D3 and 1 g/day calcium lactate for 1 week normalized calcium and PTH, and raised 1,25(OH)2-vitamin D3 to low normal levels. Conclusion: This is the first report of hypocalcaemia due to vitamin D deficiency in a patient with ‘hikikomori’ syndrome.