Carbimazole-induced lupus

We describe the case of a 50-year-old lady admitted with a 3-week history of dyspnoea and left-sided pleuritic pain associated with pleural effusion. This common clinical picture nevertheless gave rise to a significant diagnostic challenge. The medical history included a diagnosis of thyrotoxicosis made 6 months previously that was being treated with carbimazole by her general practitioner. Key-investigation results were as follows: (1) pleural fluid was sterile and exudative, with no malignant cells, (2) erythrocyte sedimentation rate, C reactive protein and D-dimer were raised, (3) antinuclear antibody, anti-dsDNA and antihistone antibodies were newly positive, (4) imaging revealed a large left ventricular mass consistent with thrombus in the absence of evidence of a myocardial infarction. Based on the above investigations we hypothesised that carbimazole had induced systemic lupus erythematosus, manifesting as serositis resulting in an exudative pleural effusion and a proinflammatory/prothrombotic state. Carbimazole was stopped. The patient's pleural effusion completely resolved and she remains asymptomatic.