Isolated Parosmia Caused by Vitamin B12 Deficiency

Abstract

Vitamin B12 deficiency classically presents with neurological or hematological abnormalities. Prior reports have shown that vitamin B12 deficiency also causes olfactory dysfunction when patients have concurrent neurological or hematologic findings. To our knowledge, this is the first case of isolated parosmia caused by vitamin B12 deficiency in the absence of neurological/hematological abnormalities or structural sinonasal disease. A 20-year-old man presented with a 3-month history of parosmic symptoms. Nasal endoscopy, brain MRI, and neurological examinations were normal. A laboratory evaluation demonstrated marked vitamin B12 deficiency without hematologic abnormalities, and oral methylcobalamin led to the complete resolution of parosmia within 3 months. Clinicians should consider vitamin B12 deficiency as a reversible cause of olfactory dysfunction.

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BibTeX RIS

BibTeX

@article{handa2026isolated,
  title = {{Isolated Parosmia Caused by Vitamin B12 Deficiency}},
  author = {Hideo Handa and Akiyuki Uzawa and Nobuaki Shu and Masahiro Mori and Satoshi Kuwabara},
  journal = {Internal Medicine},
  year = {2026},
  month = sep,
  doi = {10.2169/internalmedicine.7232-26},
  url = {https://www.jstage.jst.go.jp/article/internalmedicine/advpub/0/advpub_7232-26/_article},
  note = {CC BY-NC-ND},
}

RIS

TY  - JOUR
TI  - Isolated Parosmia Caused by Vitamin B12 Deficiency
AU  - Hideo Handa
AU  - Akiyuki Uzawa
AU  - Nobuaki Shu
AU  - Masahiro Mori
AU  - Satoshi Kuwabara
PY  - 2026
DA  - 2026/09/01
JO  - Internal Medicine
DO  - 10.2169/internalmedicine.7232-26
UR  - https://www.jstage.jst.go.jp/article/internalmedicine/advpub/0/advpub_7232-26/_article
AB  - Vitamin B12 deficiency classically presents with neurological or hematological abnormalities. Prior reports have shown that vitamin B12 deficiency also causes olfactory dysfunction when patients have concurrent neurological or hematologic findings. To our knowledge, this is the first case of isolated parosmia caused by vitamin B12 deficiency in the absence of neurological/hematological abnormalities or structural sinonasal disease. A 20-year-old man presented with a 3-month history of parosmic symptoms. Nasal endoscopy, brain MRI, and neurological examinations were normal. A laboratory evaluation demonstrated marked vitamin B12 deficiency without hematologic abnormalities, and oral methylcobalamin led to the complete resolution of parosmia within 3 months. Clinicians should consider vitamin B12 deficiency as a reversible cause of olfactory dysfunction.
SN  - 1349-7235
SN  - 0918-2918
ER  -

Abstract

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