Successful outcome of Rituximab treatment based on lymphocyte immunophenotyping in active Thyroid Eye Disease: a case report

Rituximab, an anti-CD20 monoclonal antibody that depletes B-cells, is a potential second-line treatment for moderate-to-severe active Thyroid Eye Disease that is resistant to steroids. This report comprehensively analyzes the influence of rituximab on the immune system of a patient, detailing immunophenotyping of blood, thyroid, and cervical lymph nodes before and after therapy. A 53-year-old male presented with Thyroid Eye Disease reactivation 18 months after previous treatment with intravenous methylprednisolone, and it was successfully treated with two 500 mg intravenous doses of rituximab, achieving disease inactivation. The effects of rituximab were monitored on paired blood-, thyroid- and cervical lymph nodes-derived lymphocytes by repeated ultrasound-guided fine-needle aspiration. Only after two rituximab doses Thyroid Eye Disease inactivated, when B cells were markedly reduced in lymph nodes with depletion of germinal B cells. Follicular T cell subsets and T-cell activation markers were also affected, probably due to the lack of B-cell support. Twenty-two weeks after inactivation, the patient underwent decompression surgery of the right eye due to residual proptosis. The immunophenotyping of retro-orbital tissue showed persistence of B cells, with different subsets compared with other depots. This is the first report of personalized therapy in active Thyroid Eye Disease based on monitoring tissue-resident lymphocytes. Such novel approach could lead to more targeted and effective treatments in the future.