Introduction: Subacute thyroiditis (SAT) and acute suppurative thyroiditis (AST) are two distinct inflammatory conditions but share many overlapping clinical and biochemical features, which may pose a diagnostic challenge. We report a case of SAT mimicking AST. Case: A 39-year-old female presented with a 3-week history of painful neck swelling and symptoms of thyrotoxicosis, including palpitations, heat intolerance, and diaphoresis. She had no family history of thyroid disease. On examination, she was febrile and had a smooth and tender goiter. Her blood tests showed leukocytosis with elevated erythrocyte sedimentation rate and C-reactive protein. Her thyroid function test (TFT) showed thyroid-stimulating hormone of 0.023 mIU/L and free thyroxine 4 of 32.15 pmol/L. An urgent ultrasound revealed a large, ill-defined heterogeneously hypoechoic lesion predominantly at the left lobe of the thyroid gland with mild intralesional vascularity. These were reported as features of thyroiditis with infective or early suppurative changes. Fine needle aspiration (FNA) of the lesion was attempted by the radiologist but was unsuccessful. She was treated with intravenous antibiotics and nonsteroidal anti-inflammatory drugs (NSAIDs), but symptoms persisted. Repeated ultrasound and computed tomography scans about 1 week later confirmed an enlarged thyroid gland with no obvious lesion or collection within the gland. The diagnosis was revised to SAT, and prednisolone 15 mg OD was started. This resulted in rapid improvement in her symptoms and inflammatory markers. Four weeks later, she remained asymptomatic, and prednisolone was gradually tapered off. Serial TFT monitoring showed a classic triphasic pattern with an initial hyperthyroid phase, followed by hypothyroidism before returning to euthyroidism. Conclusion SAT can present with a focal lesion on the ultrasound during the early stage of the disease, making it difficult to distinguish from a thyroid abscess due to overlapping features. Good clinical judgement guided by FNA and appropriate follow-up imaging may be helpful in differentiating between the two conditions.
Thyroiditis, Subacute ; Thyroiditis, Suppurative