Introduction: Glucocorticoids represent the therapy of choice for active and moderate-to-severe Graves' orbitopathy (GO). In some patients, rituximab, a monoclonal antibody against the cluster of differentiation (CD) 20 receptor of B-lymphocytes, can serve as a second-line or an alternative treatment. The effect of very low-dose of rituximab on the clinical activity of GO and corresponding clinical or laboratory changes is reported.
Material and methods: Changes of Clinical Activity Score (CAS) for GO, proptosis, levels of thyroid-stimulating hormone receptor antibodies, and depletion of CD19+ and CD20+ B-lymphocytes were determined in ten patients (two men and eight women) with active moderate-to-severe GO treated with a single 100-mg dose of rituximab. Correlations between differences of clinical and laboratory parameters were performed.
Results: A significant decrease of CAS was found during subsequent examinations compared to the baseline values. A significant depletion of CD19+ and CD20+ B-lymphocytes was detected after rituximab administration. Differences between follow-up and baseline levels of CD20+ positively correlated with differences in CAS after six (p < 0.05) and 12 months (p < 0.01). Differences in CD19+ levels correlated with differences in CAS after 12 months (p < 0.05) of the treatment. Two patients developed dysthyroid optic neuropathy (DON) requiring orbital decompression. No other rituximab side effects were reported during the whole study duration.
Conclusions: A single very low-dose of rituximab appears to be very well tolerated and effective enough to reduce clinical activity in active moderate-to-severe GO patients without impending DON.
Keywords: Graves' orbitopathy; clinical activity score; dysthyroid optic neuropathy; rituximab; thyroid gland.