An Unusual Presentation of Subacute Thyroiditis As Pyrexia of Unknown Origin With Normal Thyroid Functions

Subacute thyroiditis is a rare condition believed as immune-mediated inflammation of the thyroid gland that frequently manifests after a viral upper respiratory tract infection. A 52-year-old South-Asian female patient presented to Same Day Emergency Care (SDEC) with feeling unwell and sore throat. Moreover, she reported low-grade fever, fatigue, headache, and breathlessness on exertion for the past five weeks. She had a past medical history of gastroesophageal reflux disease. She had no associated cough, rigors, chills, urinary symptoms, night sweats, or weight loss. There was no history of recent travel abroad. On examination, she was tachycardic; however, there was no lymphadenopathy, palpable thyroid gland, skin rash, or signs of infective endocarditis. Routine blood analysis showed elevated erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and normal white blood cell count. Her thyroid stimulating hormone (TSH) was normal. Chest X-ray and echocardiogram were unremarkable. She was prescribed clarithromycin with no effect. After inconclusive results of the routine investigation and no response to antibiotics, a computed tomography (CT) scan of the thorax, abdomen, and pelvis (TAP) was performed, which revealed a thickened thyroid isthmus. Positron Emission Tomography (PET) scan revealed bulky appearances of the thyroid gland with diffuse increased uptake suggestive of thyroiditis. Prednisolone 30mg daily was prescribed, which was later reduced by 5mg weekly for six weeks. The patient showed improvement in symptoms, and normal ESR and CRP were achieved.