[Exercise-induced muscular weakness, myalgia and contractures. I. A clinical review]

In the differential diagnosis of intermittent claudication some rare myopathies have to be considered. The most frequent is phosphorylase deficiency (McArdle's disease). Exercise-induced muscular pain, weakness, contractures and occasionally myoglobinuria are the most prominent clinical signs. Serum creatine phosphokinase, aldolase and lactic dehydrogenase may be elevated after exertion. In the ischemic forearm test there is no rise of serum lactic acid. The enzyme deficiency can be demonstrated by histochemical and biochemical examination of a muscle specimen. Further, but more infrequent, enzymatic disturbances of glycolysis are phosphofructokinase deficiency and phosphohexoisomerase inhibitor, which also yield an abnormal ischemic forearm test and must be demonstrated histochemically and biochemically. Apart from muscular signs, myopathy with lactic acidosis is associated with palpitation, dyspnea and exhaustion, and a disproportionate rise in serum lactic acid level after exertion. Histochemically and electronmicroscopically demonstrable fat accumulation in the muscle can be a sign of a disturbance in lipid metabolism. This type of exercise-induced myopathy has been reported only in a few cases with carnitine-pylmityltransferase deficiency, which has to be demonstrated biochemically. Muscular contractures also exercise-induced but painless and reversible within seconds may be due to deficient uptake of sarcoplasmic calcium in the tubular system. Dyskalemic paralysis causes painless paresis within minutes of hours after exertion, which disappears within hours to a few days. Myopathy with tubular aggregates can be differentiated from other exercise-induced myopathies by morphology. Myotonia combined with painful contractures characterizes myopathia myotonica.