We report a case of paraneoplastic limbic encephalitis presenting with purely olfactory symptoms. For 7 weeks, a 76-year-old man experienced distorted impressions of the odour of most foods and liquids and hallucinatory olfactory perceptions without objective stimuli. The perceived odour was metallic and foul, causing loss of appetite and weight, nausea and repeated retching. No dental or ENT cause for his symptoms was found. MRI of the brain and sinuses was normal. EEG showed no focal or paroxysmal activity. CSF protein was elevated (1.17 g) and isoelectric focusing revealed oligoclonal bands (3+) in the CSF only. A paraneoplastic antibody screen was positive for anti-Hu and weakly positive for anti-amphiphysin. CT TAP revealed malignant-appearing mediastinal lymphadenopathy but no pulmonary abnormality. The patient underwent endoscopic biopsy of the enlarged subcarinal lymph nodes. Histology confirmed metastatic small cell lung carcinoma (SCLC). Clinically, he was initially intact but later developed diplopia and bilateral horizontal nystagmus on lateral gaze. His gait became ataxic, veering towards the left, and he developed asymmetrical leg weakness, L>R. Repeat MRI brain and spine showed no metastatic deposits to explain his symptoms. Olfactory abnormalities may be associated with limbic encephalitis but have never been reported as an isolated presenting symptom. Occult malignancy should be considered in new onset olfactory symptoms in the absence of other causes.
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