Endocrine Abstracts

Introduction: Alemtuzumab is an humanized monoclonal antibody used for treatment of Relapsing remitting Multiple Sclerosis (RRMS). One of its main adverse effects is thyroid dysfunction, being a fluctuating hypothyroidism the most frequent presentation. Sometimes this thyroid disturbance is so significant that it might lead to alemtuzumab withdrawal. We present two Clinical cases of hyperthyroidism secondary to alemtuzumab with different clinical courses.

Case 1 : 53-year-old woman with RRMS under treatment with alemtuzumab (1 cycle received in 2019). She was referred by the Neurology Department due to thyroid disturbance (TSH 0.2 mcU/ml) prior to starting a new cycle. Laboratory tests showed previous normal TSH values but with positive autoimmunity (TgAb and TPOAb). She was asymptomatic so clinical monitoring was decided. The patient experienced progressive clinical and analytical development of severe hyperthyroidism in the follow-up, so antithyroid drugs (ATD) were prescribed. The study was completed with an ultrasonography and radionuclide scintigraphy, which showed diffuse hypercaptant goiter; and antibodies (TRAb positive). ATD was prescribed, and she was progressively improving. After that, the patient developed several relapses after lowering the dose. For this reason, we considered treatment with radioiodine, which was effective.

Case report 2: 43-year-old woman with RRMS since 2019, under treatment with alemtuzumab and autoimmune thyroid disease since 2013, with normal function. Two months after the start of treatment with alemtuzumab, she consulted about severe hyperthyroidism. The study consisted of an ultrasonography and radionuclide scintigraphy, which showed diffuse hypercaptant goiter; and antibodies (TRAb positive). The patient presented spontaneous evolution to severe hypothyroidism two months later. We started substitution treatment, and during follow-up, the patient presented two relapses of hyperthyroidism, which was resolved after discontinuation of replacement therapy. Currently, the patient is followed and checked every six months showing thyroid stability.

Conclusions: Alemtuzumab, an effective disease-modifying drug therapy for relapsing-remitting multiple sclerosis, frequently causes autoimmune thyroid dysfunction in a significant proportion of patients. Graves’ disease and Hashimoto’s thyroiditis can have similar clinical presentations. In alemtuzumab-induced autoimmune thyroid dysfunction, additional challenges are posed by spontaneous, bidirectional switching between hyperthyroidism and hypothyroidism. Guidelines recommend monitoring thyroid function pre-treatment and every three months for four years post-treatment.