SUN-360 Recurrent Eosinophilic Pleural Effusion Due To The Use Of Methimazole

Abstract Disclosure: J. Gill: None. A. Couch: None. D. Escalante: None. A 71-year-old female with PMHx significant for COPD, chronic systolic heart failure, recurrent left pleural effusions, and stage 3 CKD, was diagnosed with hyperthyroidism in February 2023. She was started on methimazole 10mg as TSH 0.1(normal TSH 0.4-4.5Mu/L, FT4 1.4-3.5mU/L) ,T4 was 15.7 mU/L. Over the following months, her thyroid function tests were monitored, and later her T4 level had decreased to 12.5 mU/L, prompting a reduction in methimazole to 7.5 mg. Concurrently, she reported worsening shortness of breath. A physical examination revealed a left-sided neck nodule and decreased breath sounds on the left, with chest X-ray showing moderate left pleural effusion. A CT scan confirmed bilateral pleural effusions, with a small, layered right pleural effusion.US-guided thoracentesis was performed, yielding 700 mL of serosanguinous fluid. Pleural fluid analysis showed an elevated white blood cell count (1,392/µL), moderate eosinophilia (49%), and protein content of 4.4 g/dL. Thyroid function tests during this time showed FT4 21.89 and TSH 0.72, suggesting worsening hyperthyroidism. The patient was diagnosed with eosinophilic pleural effusion likely induced by methimazole. As a result, methimazole was discontinued, and plans were made for radioactive iodine therapy.Despite therapy, she continued to experience shortness of breath and recurrent pleural effusions. A second thoracentesis showed red, bloody fluid with 61,500 RBCs, protein 4.1 g/dL, and albumin 2.2 g/dL. Chest X-ray showed stable, moderate pleural effusion with left lower lobe atelectasis. Pulmonary function tests (PFTs) revealed mixed obstructive and restrictive lung disease with significant diffusion impairment, consistent with COPD and interstitial lung disease (ILD).A third thoracentesis revealed red, bloody fluid with RBC 74,000 and protein 3.2 g/dL. Subsequent follow-up showed slight improvement in pleural effusion on chest X-ray, but the left-sided effusion persisted. Diuretic therapy and low-dose prednisone were continued, with plans for further thoracentesis if needed. After one month, a fourth thoracentesis was performed, showing a red, cloudy effusion with RBC 162,400, glucose 117, and albumin 2.0 g/dL.After three months of ongoing management, the patient was stable with small to moderate left pleural effusion, slightly improved from prior visits. Thyroid function improved with FT4 at 1.48 and TSH at 2.07. She underwent two treatments of radioactive iodine (10 mCi each) for her hyperthyroidism, and no new complaints were noted. Chest X-ray showed a small left pleural effusion. At this point, her thyroid function tests were within normal limits, and the patient remained stable with no current respiratory distress, continuing oxygen therapy at 2L/min and prednisone 5 mg daily. Top of Form Bottom of Form Presentation: Sunday, July 13, 2025