Prognostic factors for thyroid-stimulating immunoglobulin normalization in moderate-to-severe Graves' orbitopathy: a 36-month longitudinal study.

Purpose: The primary objective of this study was to identify predictive factors linked to the normalization of thyroid-stimulating immunoglobulin (TSI) levels in patients diagnosed with active, moderate-to-severe Graves' orbitopathy (GO). The study also tracked the longitudinal changes in TSI levels over a 36-month period following treatment.

Methods: The study population consisted of individuals who were recently diagnosed with active, moderate-to-severe GO and received a 12-week course of intravenous methylprednisolone (IVMP) treatment. A subgroup of patients who did not respond to the initial treatment received an additional 20 Gy of radiation therapy (RTx). TSI levels were monitored at the time of diagnosis, after treatment, and subsequently every 6 months for 36 months. Normalization was defined as a TSI level below 140%. Patients were divdied into two groups with success and failure group depending on whether TSI became normal or not.

Results: Out of 83 patients, 36 (43.4%) achieved normalized TSI levels within two years post-IVMP treatment. Lower initial TSI levels (< 425%), absence of additional RTx, and early treatment initiation were associated with a higher likelihood of TSI normalization (P = 0.035, P = 0.028, P < 0.001, respectively). Notably, significant differences in TSI level reduction were observed from 18 months post-treatment between the two groups (P = 0.031). A TSI cutoff value of 413% was identified as predictive for normalization at 24 months (P = 0.002).

Conclusion: This study is the first to identify key factors that influence normalization of TSI levels in moderate-to-severe Graves' Orbitopathy. It highlights the importance of early treatment decisions, particularly for patients with initial TSI levels above 425%. Despite the treatment, less than half of the patients achieved TSI normalization within 24 months, underscoring the need for additional research to explore the relationship between TSI levels and the clinical manifestations of chronic GO.