Acute hyposmia in type 2 diabetes.

During treatment for type 2 diabetes with a diabetic diet (without medication), a 61-year-old Japanese man suddenly developed hyposmia. The fasting plasma glucose was 208 mg/dl and haemoglobin A1c was 8.6%. On investigation, there were no indications of disease of the brain, or the nasal or paranasal sinuses. The intravenous olfaction test yielded no response, indicating suspected neural hyposmia. After 6 months, the symptoms of hyposmia improved without medication, and the intravenous olfaction test results were normal. This clinical course is very similar to that seen with diabetic neuropathy of the third and sixth cranial nerves. We speculate that hyposmia in this case may have been caused by diabetic mononeuropathy of the first cranial nerve.