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.