Subacute Thyroiditis Masking as Fever of Unknown Origin: An Intriguing Case Report.

This study presents a unique case of subacute thyroiditis, which presents as prolonged high-grade fever without any other symptoms except for mild throat pain. A 46-year-old, otherwise healthy male presented with high-grade fever for more than two to three weeks and was found to have hyperthyroidism, with elevated free thyroxine levels (free T4), low thyroid-stimulating hormone (TSH) levels, elevated c-reactive protein (CRP) an inflammatory marker, and heterogeneous bilateral thyroid nodules on imaging studies. His workup was negative for infectious etiology of fever, thus favoring the diagnosis of subacute thyroiditis as the cause of fever of unknown origin (FUO). This case highlights the importance of considering subacute thyroiditis as a potential etiology in patients with FUO and the significance of a comprehensive workup to guide appropriate management.