Differential Changes in Type I And Type Ii Muscle Fibres in Rheumatoid Arthritis: A Biopsy Study

Abstract

Thirteen patients with classical or definite rheumatoid arthritis (RA) have been investigated by the application of a battery of histochemical staining methods on muscle biopsy material, viz. myofibrillar ATPase, modified ATPase method with acid preincubation, phosphorylase, glycogen (PAS), succinic dehydrogenase, NADH₂tetrazolium reductase, fat (sudan black B). Hematoxylin-eosin stain and a modified trichrome method were also used. Based on their stainability for myofibrillar ATPase the muscle fibres are classified as type I (lightly stained) and type II (darkly stained). A preferential atrophy of type II fibres is evident. A segmental degeneration of fibres accompanied by a segmental loss of enzyme activity is found in both types of fibre. It is emphasized that the type II atrophy must be the result of a more complex mechanism than simple “disuse”. One of the cases exhibits a pronounced change in the localisation of enzymes and substrates in atrophic as well as normal-sized fibres. A reversal of normal glycogen distribution between type I and type II fibres is also found. It is suggested that there are cases of RA with early and comprehensive muscle fibre changes which are best distinguished by certain histochemical methods.