Clinical Case Series of Destructive Thyrotoxicosis Associated with Hashimoto’s Thyroiditis Misdiagnosed as Graves’ Disease: Clinical Patterns, Diagnostic Pitfalls, and Hypothesized Molecular Insights

This descriptive clinical case series analyzes five cases of destructive thyrotoxicosis associated with Hashimoto's thyroiditis, historically referred to as hashitoxicosis, initially misdiagnosed as Graves' disease, highlighting a persistent diagnostic challenge in autoimmune thyroid disorders. The series includes four published cases reported between 2000 and 2025 and one unpublished case contributed by the authors. The cohort comprised three females and two males, with a mean age of 55.4 years (range: 21-69). Clinical presentations were heterogeneous, most commonly fatigue (80%), palpitations (60%), and weight changes (40%), while two patients exhibited no overt hyperthyroid symptoms.Biochemical evaluation demonstrated suppressed thyroid-stimulating hormone (TSH) levels in all cases (range: <0.000-0.13 µIU/mL), elevated anti-thyroid peroxidase (anti-TPO) antibodies in 80% (range: 41->1,000 IU/mL), and initially negative thyroid-stimulating hormone receptor antibodies (TRAb/TSI) in 60% of patients. Seroconversion to positive TRAb/TSI was observed in two cases during follow-up, suggesting autoimmune overlap rather than definitive disease transition. Imaging findings, including thyroid ultrasonography and radioiodine uptake (RAI) studies, consistently favored destructive thyroiditis over stimulatory hyperthyroidism, with heterogeneous echotexture observed in 75% of assessed cases and low or normal RAI uptake in all evaluated patients.Misdiagnosis occurred in 80% of cases, predominantly due to reliance on suppressed TSH levels without TRAb confirmation, resulting in inappropriate antithyroid drug administration in 80% and accelerated hypothyroidism in 60%. Immunopathological interpretation based on existing literature supports a predominantly Th1-mediated destructive process, in contrast to the Th2-driven antibody-mediated stimulation characteristic of Graves' disease, with rare Th1-to-Th2 immune shifts reported. Clinical outcomes ranged from spontaneous resolution to surgical intervention.This case series underscores the importance of mandatory TRAb testing, adherence to American and European Thyroid Association guidelines, and early specialist referral to reduce iatrogenic harm and improve diagnostic precision in autoimmune thyroid disease.