Muscle involvement in rheumatoid arthritis: an ultrastructural study.

An electron microscopic investigation has been carried out on muscle bioptic samples from patients affected by rheumatoid arthritis (RA). This study was undertaken to seek further ultrastructural alterations affecting striated muscles in RA pathology. Bioptic samples were collected on a total of 30 surgical interventions of hip (10), knee (8), and foot (12). This yielded three muscle types: gluteus maximus, vastus lateralis, and extensor digitorum communis. Muscle samples from 12 patients with no RA stigmata, selected to match RA patients by age and gender, constituted the control group. Tissue samples were prepared both for conventional histochemical methods and according to conventional electron microscopic procedures, including morphometric analysis. Although to a different extent in each sample, in muscles from RA vs. controls the authors observed the simultaneous presence of discrete muscular alterations such as wider separation of myofibrils, myelin figures, dilated sarcotubular system, pleomorphic mitochondria, myofibril flaking, and lipofuscin deposition in the subsarcolemmal region. In addition to a progressive atrophy, the above findings are suggestive of rheumatoid myositis and lend further support to the still poorly documented presence of an idiopathic inflammatory myopathy and inclusion body myositis associated with RA.