{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,27]],"date-time":"2026-08-27T13:23:04Z","timestamp":1787836984746,"version":"build-2784847793"},"reference-count":15,"publisher":"BMJ","issue":"8","content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Case Rep"],"accepted":{"date-parts":[[2026,8,3]]},"published-print":{"date-parts":[[2026,8]]},"abstract":"<jats:p>\n                    A man in his 40s presented with progressive gait instability and distal sensory disturbance after 2 years of \u2018hikikomori\u2019 syndrome associated with a depressive state. Neurological examination demonstrated severe sensory ataxia with sensory-dominant polyneuropathy. Serum vitamin B\n                    <jats:sub>12<\/jats:sub>\n                    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 B\n                    <jats:sub>12<\/jats:sub>\n                    and corrected calcium levels. This case suggests that prolonged social withdrawal and reduced sunlight exposure may contribute to concurrent vitamin D and vitamin B\n                    <jats:sub>12<\/jats:sub>\n                    deficiencies and that resultant hypocalcaemia may contribute to vitamin B\n                    <jats:sub>12<\/jats:sub>\n                    deficiency.\n                  <\/jats:p>","DOI":"10.1136\/bcr-2026-275337","type":"journal-article","created":{"date-parts":[[2026,8,27]],"date-time":"2026-08-27T13:05:19Z","timestamp":1787835919000},"page":"e275337","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Sensory ataxia associated with vitamin B\n                    <sub>12<\/sub>\n                    deficiency and hypocalcaemia in a patient with \u2018hikikomori\u2019 syndrome"],"prefix":"10.1136","volume":"19","author":[{"given":"Takao","family":"Hashimoto","sequence":"first","affiliation":[{"name":"Department of Neurology, Aizawa Hospital, Matsumoto, Nagano Prefecture, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Megumi","family":"Kubota","sequence":"additional","affiliation":[{"name":"Department of Neurology, Aizawa Hospital, Matsumoto, Nagano Prefecture, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yasuto","family":"Nakasone","sequence":"additional","affiliation":[{"name":"Diabetes Center, Aizawa Hospital, Matsumoto, Nagano Prefecture, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Toru","family":"Aizawa","sequence":"additional","affiliation":[{"name":"Diabetes Center, Aizawa Hospital, Matsumoto, Nagano Prefecture, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,8,27]]},"reference":[{"key":"2026082706051072000_19.8.e275337.1","article-title":"A Case of Hypocalcaemia Due to Vitamin D Deficiency in \u201cHikikomori\u201d 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