Primary central nervous system lymphoma in a patient treated with natalizumab.

A 40-year-old man with relapsing-remitting multiple sclerosis (MS) developed primary central nervous system lymphoma (PCNSL) after having received 21 doses of natalizumab monotherapy. PCNSL is a disease of the elderly, with the majority of patients being diagnosed in the 7th to 8th decade of life. Immunodeficiency, iatrogenic immunosuppression, and some autoimmune diseases are known as predisposing conditions, and in these patients PCNSL peaks in the 4th decade. Because there is no increased prevalence of PCNSL in MS, and the patient was otherwise not immunocompromised, an association between natalizumab therapy and PCNSL cannot be ruled out.