Painful Hashimoto's Thyroiditis Masquerading as Subacute Thyroiditis: Insights from two cases suggesting distinct clinical patterns

Hashimoto’s thyroiditis is typically a painless disease. In rare instances, painful Hashimoto’s thyroiditis may clinically mimic subacute thyroiditis and lead to improper treatment or delayed therapy. Herein, we present two cases of painful Hashimoto's thyroiditis, each representing different clinical manifestations of this disease. In both cases, elevated antithyroid antibodies and elevated ESR were observed during the onset of the illness. In case 1, a 53-year-old woman had a history of Graves' disease and experienced transient thyroid pain without steroid treatment. Eventually, hypothyroidism ensued. A fine-needle aspiration cytology confirmed the diagnosis of Hashimoto's thyroiditis in the patient. In contrast, in case 2, a 66-year-old woman with no prior thyroid disorders, presented with recurrent episodes of thyroid pain. Although an initial steroid therapy provided temporary relief, tapering the steroid dose led to a resurgence of pain. Ultimately, total thyroidectomy was performed, which ameliorated painful sensation. A histopathological examination of the excised thyroid tissue revealed Hashimoto's thyroiditis. These two cases have expanded the clinical spectrum of uncommon painful Hashimoto’s thyroiditis. Taken together with the cases reported in the literature, we further identify two distinct clinical patterns (Rapid vs. Slow progression) based on clinical presentation. • Rare diagnostic challenge: Painful Hashimoto thyroiditis is an uncommon, intensely inflammatory phenotype that mimics subacute thyroiditis and often delays diagnosis. • Two-pattern prognostic classification: Pattern 1 (rapid, ∼20%) and Pattern 2 (slow, ∼80%) stratify course and treatment needs. • Pattern 1 course and response: Rapid progression to permanent hypothyroidism within months; typically, responsive to NSAIDs and thyroid hormone replacement. • Pattern 2 course and management: Slow, relapsing pain with frequent steroid dependence and a high rate of definitive thyroidectomy. • Autoimmune trigger signal: 32.9% of 70 reported cases had prior Graves disease, implicating autoimmune phenotype conversion as a possible trigger. • Clinical implication: Use the subtype to guide care - conservative medical therapy for rapid cases; earlier surgical consideration for recurrent, steroid-dependent cases to reduce prolonged immunosuppression.