Clinical benefits and immunopathological correlates of intravenous immune globulin in the treatment of inflammatory myopathies.

High-dose intravenous immune globulin (IVIG) is emerging as a promising therapy for patients with inflammatory myopathies who have become unresponsive to, or cannot tolerate, conventional therapies. In a double-blind, placebo-controlled study, using objective criteria for improvement, IVIG demonstrated moderate to dramatic improvement in 75% of the patients with dermatomyositis. Preliminary results from a controlled study in inclusion-body myositis show that IVIG may also exert a mild benefit, but only in a small number of patients and in certain muscle groups. In some patients with polymyositis, IVIG is reported to be of benefit but controlled studies have not yet been completed. Immunocytochemical, immunological and in vitro studies on the patients' repeated muscle biopsies and follow-up sera showed that IVIG exerts its action in inflammatory myopathies by: (i) inhibiting myotoxic cytokines, such as TNF-alpha and IL-1; (ii) blockade of Fc receptors on endomysial macrophages interfering with Fc receptor-mediated phagocytosis; and (iii) inhibiting the uptake of C3 and intercepting the formation and deposition of membranolytic attack complex on the endomysial capillaries.