Alemtuzumab-related thyroid disease in people with multiple sclerosis is associated with age and brainstem phenotype at disease onset.

Alemtuzumab-induced reconstitution GD may result from early and increased cross-reactivity between antigens common to the brainstem and thyroid, or presence of shared Human Leukocyte Antigen (HLA) alleles that determine brainstem and thyroid involvement. We suggest cautious use of alemtuzumab in younger (≤32 years) pwMS with early brainstem involvement, especially those actively planning pregnancy, where alternative therapies are readily available.