Abstract
BACKGROUND: Pyrexia of unknown origin is a difficult and challenging problem for the physician. Endocrine disorders, such as subacute thyroiditis, rarely present with pyrexia of unknown origin. Subacute thyroiditis can have a broad spectrum of clinical presentations including fever and biochemical thyrotoxicosis without overt signs or symptoms. CASE PRESENTATION: A previously healthy 42-year-old Sri Lankan Sinhalese man was extensively investigated for a prolonged fever of 3 weeks with high inflammatory markers. He had mild tenderness over his neck with cervical lymphadenopathy with no thyrotoxic symptoms or signs. An ultrasound scan revealed an enlarged thyroid with increased vascularity and he had suppressed thyroid-stimulating hormone with elevated free thyroxine and free triiodothyronine hormone levels. Fine-needle aspiration cytology confirmed thyroiditis. He responded well to low-dose steroids. CONCLUSION: Subacute thyroiditis should be considered in the diagnostic workup of pyrexia of unknown origin even in the absence of overt toxic symptoms of thyroid hormone excess.