Mustafa Buğra BOZDOĞAN, Teoman ŞAKALAR, Mehmet Emin YERLİ, Ayten OĞUZ
Endocrinology Research and Practice - 2026;30(2):130-133
A case of subacute thyroiditis (SAT) associated with pembrolizumab, is presented with unusual symptoms. A 36-year-old male patient with renal cell carcinoma undergoing pembrolizumab therapy presented with complaints of sweating, fatigue, and pain in the left lower thyroid lobe 1 week after completing his fourth treatment cycle. There was no recent history of viral infection or vaccination. On physical examination, the patient's vital signs were normal and palpation revealed tenderness in the left thyroid lobe. Laboratory tests showed thyrotoxicosis and a C-reactive protein (CRP) level of 11.2 mg/L; thyroid antibodies were negative. Thyroid ultrasound and scintigraphy revealed thyroiditis, and the patient was diagnosed with SAT. The CRP levels were moderately elevated, so ibuprofen was prescribed, but symptoms worsened. During the 2-week follow-up, CRP levels increased to 14.9 mg/L. Pembrolizumab therapy was postponed, and steroid therapy was initiated. The patient reported improvement in symptoms 1 day after starting steroid therapy. Thyroid function returned to normal after 2 weeks. Steroids were gradually tapered and discontinued in the fifth week. Pembrolizumab therapy was restarted, and the patient remained euthyroid 3 months later. Thyrotoxicosis is an important side effect that can be seen during treatment with pembrolizumab. However, SAT is rare and should be considered in the differential diagnosis.
