A Case of Unilateral Graves’ Disease with a Previously Unreported Bilateral–Unilateral–Bilateral Imaging Pattern

AbstractBackground/Objective Unilateral Graves' disease (UGD) is a rare phenotypic variant of Graves' disease characterized by asymmetric radionuclide uptake confined to a single thyroid lobe. Its natural history remains poorly understood. We report a case to elucidate the temporal evolution of lobar involvement using serial thyroid scintigraphy. Case Report A 42-year-old woman initially presented with classic bilateral Graves' disease, confirmed by Tc-99m pertechnetate scintigraphy showing diffuse bilateral uptake. She achieved and maintained euthyroidism for over 18 months on low-dose carbimazole. After treatment withdrawal, she relapsed with subclinical hyperthyroidism, and repeat scintigraphy demonstrated marked unilateral uptake confined to the right lobe, consistent with UGD. Following definitive radioiodine (I-131) therapy, a repeat scan performed one month later revealed restoration of bilateral uptake with persistent asymmetry, completing a bilateral → unilateral → bilateral scintigraphic sequence. Discussion This case demonstrates dynamic functional variability in lobar thyroid activity during the course of Graves' disease. The observed unilateral uptake was not a fixed or static phenomenon and evolved over time. The return to bilateral uptake in the post-radioiodine setting suggests that both lobes retained functional responsiveness, highlighting the potential for transient asymmetry in autoimmune thyroid stimulation. Conclusion This is the first documented case demonstrating a complete bilateral–unilateral–bilateral scintigraphic cycle in Graves' disease, with the final transition occurring after radioiodine therapy. Unilateral uptake on thyroid scintigraphy should not be assumed to represent a permanent pattern, and awareness of such variability may assist clinicians in interpreting atypical imaging findings and planning appropriate follow-up.