Elevated serum thyroid stimulating immunoglobulin linked to failure of first-line intravenous methylprednisolone monotherapy in moderate-to-severe thyroid eye disease.

Purpose: To assess factors associated with failure of intravenous methylprednisolone (IVMP) monotherapy as the first-line treatment for thyroid eye disease (TED) and to identify patients who might benefit from supplementing mycophenolate mofetil (MMF) to IVMP.

Methods: Data for all patients with TED treated with IVMP according to the EUGOGO protocol in our center between 2016-2021 were retrospectively analysed.

Results: Forty-seven patients (mean age 51.32 ± 14 years, 27 females) were enrolled. The mean time from first reported symptoms to first IVMP treatment was 12.1 ± 5.59 months (range 0-120). The mean clinical activity score (CAS) before treatment and at a mean of 5 and 12.2 weeks after treatment initiation was 6.00, 2.96, and 1.81, respectively (P < 0.01). Twenty-one patients (44.68%) were recommended second-line treatment: nine due to no response or worsening of CAS, six due to partial response, four with good response but early relapse after completion of treatment, and one due to late relapse. Eighteen of those 21 patients received second-line treatment which included rituximab (n = 7), MMF (n = 6), a second course of IVMP (n = 4), and tocilizumab (n = 1). Serum thyroid-stimulating immunoglobulin (TSI) levels were higher in patients who received second-line treatment compared with patients who responded well to first-line IVMP monotherapy at presentation (2135% vs 1159%, P = 0.05) and after completion of first-line treatment (2201% vs. 986%, P = 0.043).

Discussion: TED patients requiring second-line treatment after failed IVMP monotherapy had higher baseline and post-first-line treatment serum TSI levels. Those with elevated TSI may benefit from dual therapy (IVMP and MMF) and require closer monitoring.