Effects of fixed dose versus weight-based tocilizumab on thyroid eye disease: a single-centre retrospective observational pilot study

PURPOSE: To observe the therapeutic efficacy of tocilizumab administered at a fixed dose versus a body weight-dependent dose for treating thyroid eye disease (TED). METHODS: A single-centre retrospective observational Pilot Study analyzed 28 patients diagnosed with thyroid eye disease (TED). These patients were treated at the Department of Ophthalmology, Second Affiliated Hospital of Harbin Medical University from February 2023 to February 2025. Of these patients, 16 before August 2024 received a fixed dose of 320 mg tocilizumab, while 12 after August 2024 received a weight-based dose of 8 mg/kg. The treatment outcomes were assessed based on age, duration of TED, thyroid status, reduction in clinical activity score (CAS), and changes in proptosis. RESULTS: The cohort included 15 males (53.6%) and 13 females (46.4%), with a mean age of 50.75 ± 12.65 years. Most patients had Graves' hyperthyroidism (17 cases, 60.7%). The duration of TED ranged from 1 to 240 months, with a median of 12 months. At 24 weeks post-treatment, reduction in CAS was observed in 24 patients (85.7%), while 4 (14.3%) experienced no change or worsening. The CAS score decreased significantly from 4.2 ± 1.6 to 2.3 ± 1.5, averaging a reduction of 1.9 ± 1.4. Proptosis reduction averaged 1.2 ± 1.4 mm in the right eye and 1.0 ± 1.3 mm in the left eye. Overall, 9 patients (32.1%) showed significant clinical response, while 11 (39.3%) had a partial response, resulting in an overall response rate of 71.4%. Initial CAS score was identified as an independent predictor of improvement, whereas age, TED duration, dosing regimen, and thyroid antibody status were not significant predictors. No statistically significant differences were found between the fixed-dose and weight-based groups in terms of improvements in CAS scores, ocular retraction, or distribution of therapeutic responses. CONCLUSION: Tocilizumab improves CAS scores and reduces proptosis in patients with TED, demonstrating robust efficacy and acceptable safety. The initial CAS score is the primary predictor of tocilizumab efficacy, with higher initial scores correlating with greater improvement. No statistically significant differences in efficacy were detected between the fixed-dose regimen (320 mg) and the weight-based dose regimen (8 mg/kg).