Rituximab has been documented to be an effective treatment for autoimmune diseases with contribution of B cells. We report a case of antisynthetase syndrome with a history of EBV-induced lymphoma which developed a pemphigus vulgaris. Rituximab was effective both on polymyositis and on pemphigus. Fifteen months later, the patient died from a septic shock after the first cyclophosphamide infusion for amyloidosis while the B cell population remained depleted. Rituximab may be a good alternative to immunosuppressive drugs in polymyositis and pemphigus especially in lymphoma-risk patients. However, it did not prevent progression to secondary amyloidosis and the fatal infection developed in this patient raises the question of whether a prolonged B cell depletion with rituximab contributes to a greater risk of infection.