6 - Progressive Systemic Sclerosis: Skeletal Muscle Involvement

Abstract

Despite the paucity of specific complaints referable to skeletal muscle, the majority of PSS patients have evidence of a primary myopathy, characterized by the insidious onset of mild proximal muscle weakness. Laboratory abnormalities include slight but significant elevation of serum aldolase and occasionally of serum CPK activity, increased urine creatine and reduced urine creatinine excretion, and increased polyphasic potentials of normal or decreased amplitude and duration. Muscle biopsy specimens tend to show increased interstitial fibrosis with less prominent inflammation or degeneration of myofibrils. Although rapid deterioration of muscle strength may occur rarely in the untreated state, most patients will have a stable or very slowly progressive course unaffected by the use of corticosteroid therapy. The unusual PSS patient with clinical and laboratory findings more in keeping with the ‘inflammatory’ myositis of PM/DM and MCTD must be identified, however, since such individuals may benefit greatly from the administration of corticosteroids.