Endocrine Abstracts

Background: Thionamides are a class of drugs used to control thyrotoxicosis. A wide range of systemic adverse effects have been described, including agranulocytosis, rash, fever, arthralgia, hepatitis and even drug-induced lupus. Besides, there are some uncommon events related to their use, such as pleural effusion (only eight cases have been previously reported). We report a case of methimazole-induced eosinophilic pleural effusion.

Case: Our patient is a 77-year-old female diagnosed with Graves’ disease on august 2022, one month after SARS-CoV-2 infection. She started treatment with methimazole 30 mg daily right after the diagnosis. 4 weeks after starting thionamides, the patient developed severe dyspnoea, tachycardia and chest pain, even though thyroid hormones were within normal limits. Chest X-Ray showed extensive right-sided pleural effusion without mediastinal deviation. Blood test showed elevated C-reactive protein and eosinophilia. Thoracentesis result showed exudative fluid with eosinophilia (27% eosinophils); cytology and adenosine deaminase were negative, as well as the result of multiple pleural fluid cultures. She was admitted to our hospital. Blood cultures, IGRA, and autoinmunity tests (antinuclear antibodies, antineutrophil cytoplasmic antibody and antimyeloperoxidase) were performed, all of them came back negative. Total body CT scan didn´t show suggestive signs of neoplastic disease. Due to her age and comorbidities, she was not a candidate for pleural biopsy, so our patient was discharged after complete resolution of the pleural effusion, which required three evacuating thoracenteses procedures. Patient kept on using carbimazole. Two months after hospital discharge, we suspected that carbimazole was the potential cause of her pleural effusion, so the drug was discontinued. She was then referred to radio-iodine ablation with subsequent total resolution of the thyrotoxicosis. One month later, chest X-ray showed complete resolution of the pleural effusion without new recurrence.

Conclusion: Although the temporal relationship between the carbimazole use and the development of the effusion was clear, and the most common causes for pleural effusion were excluded, discontinuation of carbimazole was delayed and as a result the patient suffered from several recurrences of the effusion. This case highlights the relevance of keeping in mind the potential adverse events related to the use of anti-thyroid drugs. Some of them, although rare, are associated with severe and even life-threatening consequences. In these cases, definitive treatment alternatives to control the thyrotoxicosis are mandatory to avoid uncontrolled thyroid disease.