Serum Biomarkers Linked to Disease Activity, Severity, and Methylprednisolone Response in Graves' Orbitopathy: A Proteomic Study.

Purpose: To identify biomarkers related to disease activity, severity and response to intravenous methylprednisolone (IVMP) in Graves' orbitopathy (GO), and to evaluate differences in serum proteome between GO, IgG4-related orbital disease (IgG4-ROD) and idiopathic orbital inflammation (IOI). Methods: Serum proteomics targeting 368 inflammatory proteins (Olink Explore Inflammation panel) was performed on biobank samples from patients with GO (n = 111), IOI (n = 16), IgG4-ROD (n = 10), and healthy controls (n = 25). GO activity, severity and response to IVMP were assessed retrospectively. Differentially expressed proteins (DEPs) were defined as Log2-fold change <-0.5 or >0.5 and false discovery rate (FDR)-adjusted P < 0.05. Results: No DEPs were associated with GO activity or severity. No DEPs linked to IVMP response were seen after FDR correction, likely because of limited sample size (22 responders vs. 16 non-responders). However, five top-ranked proteins related to IVMP response prior to FDR correction were further evaluated by Luminex or ELISA, showing significantly higher VEGF-A in IVMP non-responders. Receiver operator characteristic analysis showed that VEGF-A predicted treatment response with an area under the curve (AUC) of 77.3% (sensitivity = 77.3%, specificity = 75%). Combining VEGF-A and thyroid stimulating immunoglobulins improved predictive accuracy, especially in patients receiving standard IVMP treatment for moderate-to-severe disease (AUC 84%, sensitivity 91.7%, specificity 75%). Compared to healthy controls, 105 DEPs were found in GO, 83 in IOI and 57 in IgG4-ROD. Forty-eight DEPs were differentially expressed across all three conditions. Conclusions: Serum VEGF-A is increased in IVMP non-responders and thus may be a biomarker for predicting treatment response in GO. Furthermore, GO shares immunopathobiological features with IOI and IgG4-ROD.