Emergence of rheumatoid arthritis following exposure to natalizumab.

We report a patient with relapsing-remitting multiple sclerosis, who developed rheumatoid arthritis after exposure to natalizumab. While some multiple sclerosis therapies are known to unmask autoimmune conditions, natalizumab is rarely implicated as a cause of alternative autoimmunity. This case illustrates an unusual clinical scenario which may support recent scientific work suggesting that, when natalizumab blocks T helper 1 cells from entering the central nervous system, T helper 17 cells may continue to migrate into immune-privileged spaces and cause pathologic inflammation.