Methimazole associated eosinophilic pleural effusion: a case report

Area of Science:

• Endocrinology
• Pulmonology
• Pharmacology

Background:

• Anti-thyroid drugs, including thionamides like methimazole, propylthiouracil, and carbimazole, are used to treat hyperthyroidism.
• Adverse reactions to these drugs can include fever, rash, arthralgia, agranulocytosis, and hepatitis, often considered hypersensitivity reactions.
• Previous reports have documented five cases of pleural effusion associated with thionamides.

Observation:

• A 75-year-old male with newly diagnosed hyperthyroidism developed unilateral pleural effusion and pleuritic chest pain six days after initiating methimazole.
• Laboratory tests revealed elevated C-reactive protein and erythrocyte sedimentation rate, with normal white blood cell count and liver enzymes.
• Imaging confirmed a moderate right pleural effusion, which ultrasound identified as a loculated, eosinophilic exudate.

Findings:

• The temporal association between methimazole use and pleural effusion, coupled with the exclusion of infectious, neoplastic, and autoimmune causes, strongly suggested a hypersensitivity reaction to methimazole.
• Discontinuation of methimazole and initiation of corticosteroid therapy resulted in complete resolution of the pleural effusion over three months.

Implications:

• This case highlights methimazole as a potential cause of drug-induced eosinophilic pleural effusion.
• Clinicians should consider methimazole-induced hypersensitivity when evaluating patients with unexplained pleural effusion, especially those on anti-thyroid medication.
• Increased awareness of this rare adverse reaction is crucial for timely diagnosis and management of patients receiving thionamide therapy.