Subacute Thyroiditis: A Rare Cause of Pyrexia of an Unknown Origin

Subacute thyroiditis is inflammation of the thyroid gland, classically presenting with neck pain or discomfort and sometimes with associated diffuse tender goiter and overt hyperthyroid symptoms. Only a few rare cases of subacute thyroiditis presenting as pyrexia of unknown origin (PUO) without any of the aforementioned clinical features have been reported in the literature. A 62-year-old male, with a past history of diabetes mellitus, presented with a history of intermittent fever lasting for one month duration. He did not have any significant localizing symptoms, except for a mild headache, and his examination findings were unremarkable as well. Investigations revealed a high erythrocyte sedimentation rate (ESR), high C-reactive protein (CRP) levels, and a deranged thyroid profile, with high free T3 and T4 and suppressed thyroid-stimulating hormone (TSH) levels, suggestive of subacute thyroiditis. The diagnosis was further reinforced by the findings of a supportive ultrasound scan of the neck. The patient was started on steroids, to which he showed a significant clinical and biochemical response. Here, we aim to highlight atypical presentations of subacute thyroiditis and the importance of early consideration of endocrine diseases in the workup of PUO, sometimes even in the absence of suggestive clinical features.