[Increased disease activity in a case of multiple sclerosis after switching treatment from fingolimod to natalizumab].

A 42-year-old woman diagnosed with multiple sclerosis (MS) at the age of 37 was initially treated with interferon-β IM. The frequency of clinical relapses was twice in 4 years. At the age of 41, due to difficulty in administering muscle injections, an oral medication fingolimod was started. However, it was discontinued after a month due to decreased lymphocyte count, following which natalizumab was administered. The number of relapses increased 3 times in eleven months, and the number of T2 lesions on the MRI increased from 12 to 23. Natalizumab was discontinued because the test for the anti-natalizumab antibody was positive. It was suspected that both, the rebound syndrome caused by fingolimod cessation and the drug neutralization by anti-natalizumab antibodies, were associated with the exacerbation of disease activity. Thus, careful attention should be paid to potential occurrence of these events post switching between disease-modifying drugs for treating MS with high activity.