Background/aims We evaluated longitudinal autoantibody changes after intravenous methylprednisolone (IVMP), compared them with those in untreated patients and identified prognostic factors for treatment response.

Methods In this single-centre, retrospective, observational study, a total of 163 individuals diagnosed with moderate-to-severe thyroid eye disease were enrolled and followed for 12 months. Depending on whether IVMP was administered, we divided the patients into treatment and control groups. Based on the effect of IVMP on TSH receptor (TSH Rc) antibody level, we divided the patients into Ab declined and Ab not declined groups.

We evaluated the time, group and interaction associations with the longitudinal autoantibody titres over 12 months using generalised estimating equations. Using multivariable logistic regression, we investigated the prognostic factors for a poor response to IVMP.

Results In the IVMP group, the TSH Rc antibody (Ab) titre decreased rapidly for 6 months and then decreased slowly until 12 months, becoming similar to the control group at 12 months. This suggests a difference in the decreasing pattern over time between the IVMP and control groups (group and time interaction p=0.029). Total cholesterol (OR 1.0217 (95% CI 1.0068 to 1.0370), p=0.0043) was a significant prognostic factor for the steroid response. The threshold total cholesterol value to distinguish between Ab declined and Ab not declined was 186 mg/dL.

Conclusion IVMP significantly decreased the TSH Rc Ab level for the 3 months after treatment, compared with the no-treatment group, but the groups did not differ significantly after 12 months. Patients with high total cholesterol levels generally showed a poor response to IVMP.