Controlled clinical trials with high-dose
intravenous immunoglobulin (
IVIg) have been conducted in patients with DM and IBM, but not PM. A double-blind placebo-controlled study in DM patients, resistant or partially responsive to conventional
therapies, showed that
IVIg is very effective in improving both the muscle strength and the
skin rash. The clinical benefit, which was impressive in patients with early disease, was associated with improvement in the muscle cytoarchitecture. Quantitative histological studies in repeated muscle biopsies showed a statistically significant increased in the size of muscle fibers and the number of capillaries with normalization of the capillary diameter. Resolution of the aberrant immunopathological parameters including interception of complement activation products and downregulation of T cells, ICAM-I, VCAM,
TGF-beta and
MHC-I molecules was also noted. In IBM,
IVIg showed marginal, and non statistically significant, improvements in muscle strength. Up to 20% of patients however, demonstrated clinical improvement with increased
activities of daily living while certain muscle groups, such as the muscles of swallowing, showed significant improvements compared to placebo implying mild regional benefits. In PM, small uncontrolled series have shown improvements in muscle strength in up to 70% of the
IVIg-treated patients. Because PM, as a stand-alone clinical entity, is a very
rare disease, completion of controlled trials will be very difficult.