[Rare viral infections during immunosuppressive therapy: a "normal" side effect?].

The use of biologicals in the therapy of rheumatic diseases allows more effective treatment of patients with very active disease. Such regimens, however, can induce a more severe treatment-related immunosuppression and, as a consequence, opportunistic infections that are rarely seen with conventional immunosuppressive therapy appear to occur more frequently. The majority of these opportunistic infections are common viral infections which become latent and only cause severe disease if they are reactivated in a severely immunocompromised host. However, some of the newer biologicals, especially natalizumab, efalizumab or rituximab, appear to carry a special risk for the reactivation of JC polyoma virus manifesting as progressive multifocal leukoencephalopathy, a severe, untreatable and often fatal encephalitis. Therefore, such treatments should be used with caution in patients who have been or are being treated with combined immunosuppressive therapy including corticosteroids. Elderly patients are specifically at risk for this "normal" side effect.