Methimazole is a thionamide drug that inhibits the synthesis of thyroid hormones by blocking the oxidation of iodine in the\nthyroid gland.We report a case of methimazole-induced recurrent pleural effusion. A 67-year-old female with recently diagnosed\nGravesâ?? disease on methimazole 20mg daily was admitted with dyspnea and new onset atrial fibrillation with rapid ventricular\nrate. Chest X-ray revealed a unilateral right pleural effusion, which was consistent with a transudate on thoracocentesis. She was\nmanaged as a case of congestive heart failure and methimazole dose was increased to 30 mg daily. She was readmitted twice with\nrecurrent right pleural effusion.Thefluid revealed an exudative process on repeat thoracocentesis.CT scan of the chestwith contrast\nshowed mediastinal lymphadenopathy and a diffuse ground glass process involving the right lower lobe suggestive of pneumonitis.\nBronchoalveolar lavage showed neutrophil predominant fluid, and cytology and adenosine deaminase were negative. Patient also\nhad an endobronchial ultrasound guided biopsy of the lymph nodes (EBUS). She was treated empirically with steroids 40 mg for\n10 days and themethimazole was also discontinued.The antinuclear antibodies (ANA) came back positive with a speckled pattern;\nantineutrophil cytoplasmic antibody (c-ANCA) and antimyeloperoxidase were also positive. The effusion resolved but recurred\non rechallenge with methimazole. She was referred for urgent thyroidectomy. The patientâ??s repeat chest X-ray showed complete\nresolution of the pleural effusion after stopping themethimazole. Fewweeks later, repeat ANCA and antimyeloperoxidase antibody\nwere both negative. Our case report highlights the importance of the recognition of a rare side effect of methimazole. Timely\ndiagnosis would ensure that appropriate treatment is given.
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