Fever of unknown origin as the major manifestation of subacute thyroiditis

Fever of unknown origin is a commonly encountered medical problem. Most common causes include infections, malignancy, and connective tissue diseases. Endocrine causes are rare but are well documented. While fever is common in some endocrine disorders, fever of unknown origin as the sole presenting feature is very rare. We describe a case report of a 63-year-old male who presents with fever of unknown origin. Imaging and biopsy results confirmed the diagnosis of subacute thyroiditis. He was started on prednisone with a good response. We conclude that subacute thyroiditis should be considered in the work up of fever of unknown origin even in the absence of classical signs and symptoms. LEARNING POINTS: Fever of unknown origin is a rare sole presentation of subacute thyroiditis. The classic signs and symptoms may not be manifest at the time of presentation. Normal thyroid function tests and elevated markers of inflammation often make infections, malignancy and autoinflammatory conditions the prime consideration. Imaging of the thyroid gland may point to a morphologic aberration and prompt a thyroid biopsy. After exclusion of infection, a rapid response to steroids may be both diagnostic and therapeutic.