Ultrastructural changes in skeletal muscle in polymyalgia rheumatica

Skeletal muscle from 21 patients with clinical confirmed polymyalgia rheumatica (PMR) were examined electronmicroscopically. The changes were classified according to 15 ultrastructure criteria. The focal changes have a regressive character and, while they are nonspecific, the systematic assessment of all criteria produced a characteristic pattern in which the ultrastructural picture of skeletal muscles provided a certain profile in cases of PMR. The functionally most important ultrastructural change concerns the mitochondria. Deposition and deformation of crystals result in mitochondrial changes which are structurally definable and are harmful to cell respiration. They are compensated by new formation and accumulation of mitochondria. Comparative analysis of regressive skeletal changes and of processes in the region of the media of the muscular arteries demonstrates analogous morphological changes which point to a common harmful and overlying systemic process in PMR and giant cell arteritis. Changes in the ultrastructure of the kind and degree described cannot be explained by inflammatory or noninflammatory arterial occlusions.