Hydroxychloroquine-Induced Bradycardia in a Male Patient With Sarcoidosis: A Case Report.

Hydroxychloroquine (HCQ) is often used in sarcoidosis as a steroid-sparing agent. Though generally safe, rare cardiac side effects like bradycardia can occur, especially in patients with underlying cardiac vulnerability. A 40-year-old South Asian male with biopsy-proven sarcoidosis, stable on HCQ, azathioprine, and prednisolone, presented with low-grade fever, vomiting, and diarrhea. He was febrile, but hemodynamically stable. Labs showed leukocytosis, elevated CRP, and prerenal acute kidney injury. IV hydrocortisone was started, after which he developed sudden asymptomatic bradycardia (30-40 bpm). ECG revealed sinus bradycardia with partial right bundle branch block. Cardiac enzymes and echocardiogram were normal. Despite switching to methylprednisolone, bradycardia persisted. Given the temporal correlation and exclusion of other causes, HCQ-induced bradycardia was suspected. HCQ was discontinued, and the heart rate normalized within 48 h. This case highlights the rare risk of HCQ-induced bradycardia, which can unmask or worsen occult cardiac sarcoidosis, even after long-term therapy. Clinicians should maintain vigilance for conduction abnormalities in sarcoidosis patients receiving HCQ, particularly when immunosuppressive regimens are modified.