A Rare Case of Painful Thyroiditis: Initially Suspected as Subacute Thyroiditis, Ultimately Diagnosed as Hashimoto Thyroiditis

Background: Painful Hashimoto thyroiditis (pHT) is a rare variant of Hashimoto thyroiditis (HT). Because neck pain, raised inflammatory markers and an initial response to glucocorticoids are shared with subacute thyroiditis (SAT), pHT is frequently misdiagnosed. We describe a steroid-dependent case to highlight the features that help distinguish pHT from SAT. Methods: A 49-year-old Chinese woman with a 10-year history of goiter and treated hypothyroidism presented with recurrent painful neck swelling initially diagnosed as SAT. Evaluation comprised thyroid function, autoantibodies, inflammatory markers, grayscale, Doppler and contrast-enhanced ultrasound, ultrasound-guided 18-gauge core-needle biopsy, and, after thyroidectomy, histopathology, immunohistochemistry and immunoglobulin gene rearrangement analysis. Results: The erythrocyte sedimentation rate was markedly elevated, thyroid autoantibodies were modestly positive, and no thyrotoxic phase was documented. Pain relapsed during each of two prednisone tapers, despite the addition of mycophenolate mofetil to the second. Biopsy and surgical histology showed HT, with no evidence of malignancy, IgG4-related disease or B-cell clonality. Total thyroidectomy resolved the pain, and the patient remained pain-free on levothyroxine at 24-month follow-up. Conclusions: Recurrent “SAT” in a patient with pre-existing autoimmune thyroid disease, especially when pain relapses with each steroid taper, should prompt tissue diagnosis; total thyroidectomy provides durable relief in refractory pHT.