Multiple sclerosis reactivation postfingolimod cessation: is it IRIS?

Although few recent studies have reported efficacy and safety data among patients with multiple sclerosis (MS) switching between immunotherapies, data on the mechanism of rebound activity postwithdrawal of fingolimod in patients with MS is scarce. A 36-year-old woman developed severe reactivation of her disease within 7 weeks of fingolimod's withdrawal despite the absence of breakthrough disease during the 8-week natalizumab washout period previously. The clinical presentation and radiological features were described indicating the diagnostic challenge given the potential risk of developing progressive multifocal leucoencephalopathy. The severe reactivation postwithdrawal of fingolimod could be due to the immune reconstitution inflammatory syndrome (IRIS) given the abrupt rise in lymphocyte count. Patients who discontinued fingolimod might be at risk of developing IRIS resulting in disease reactivation in the washout period.