Evaluation of the relationship between laboratory parameters at initial presentation and clinical course in patients diagnosed with subacute thyroiditis

Subacute thyroiditis (SAT), also known as giant cell or De Quervain's thyroiditis, is a clinical condition characterized by thyroid inflammation. In this study, we aimed to evaluate the clinical and laboratory features at initial presentation, the relationship between acute-phase reactants and thyroid function tests (TFTs), and the impact of treatment modalities on long-term clinical outcomes in patients diagnosed with SAT. This retrospective study included 49 patients aged 18 years or older who were diagnosed with SAT between January 1, 2018, and January 1, 2024. Demographic characteristics, clinical findings, laboratory parameters [thyroid-stimulating hormone (TSH), free T3, free T4, Creactive protein (CRP), erythrocyte sedimentation rate (ESR)], ultrasonographic (USG) features, and treatment approaches were recorded. Correlations between CRP/ESR and TFT parameters, as well as differences between treatment groups, were statistically analyzed. The mean age of the patients was 50.3 ± 11.7 years. During follow-up, hypothyroidism developed in 34.69% of patients, while 63.26% remained euthyroid. A negative correlation was observed between CRP and TSH, and a positive correlation between CRP and T3 (p<0.05). No significant correlation was found between ESR and TFT parameters. NSAIDs were used as the first-line therapy, and steroids were initiated in cases unresponsive to NSAIDs. Patients receiving steroids had significantly higher CRP and neutrophil-to-lymphocyte ratio (NLR) levels. No significant difference was observed in CRP or ESR values between patients who developed hypothyroidism and those who remained euthyroid. USG revealed unilateral involvement in half of the patients and bilateral involvement in the other half. Although inflammatory markers such as CRP are useful in predicting disease severity and treatment requirements, they are not sufficient alone to predict the development of long-term hypothyroidism. Comprehensive evaluation of clinical, laboratory, and imaging findings is crucial in the management of SAT. Key Words: subacute thyroiditis, hypothyroidism, treatment, steroid