Muscle pathology in polymyalgia rheumatica: histochemical and immunohistochemical study.

Abstract

Immunohistochemical studies were performed on muscle biopsy specimens of polymyalgia rheumatica (PMR) to evaluate the extent of muscle and peripheral nerve involvement. The routine histochemistry revealed a mild variation of fiber size, type 2 fiber atrophy and type 2A or 2B fiber deficiency. In 63% of the PMR cases small angular fibers, pyknotic nuclear clumps or target-targetoid fibers were observed, suggesting neurogenic changes, although abnormalities were mild in degree. In immunocytochemical studies, neither major histocompatibility complex (MHC) class 1 nor class 2 products were expressed on the muscle surface membrane of PMR. But regarding intramuscular vessels, MHC class 2 products were distinctly visualized. On serial sections, combined deposits of IgG and Clq in perimysial arteries were seen in 38% of PMR. These results suggest that arteries of small caliber might be involved in immunopathological processes, causing muscle and peripheral nerve damage.