[Postinfectious myopathy. An important differential diagnosis in muscle pain]

Following a viral infection of the upper respiratory tract a 63-year-old woman developed a postinfectious myopathy with nonprogressive muscle weakness and diffuse muscle pain. Electromyography revealed typical changes of a myopathy with low-amplitude, splintered voluntary potentials and prematurely dense interference pattern, without additional abnormal spontaneous activity as a pointer to an acute inflammatory process. Muscle biopsy showed moderate focal atrophic and inflammatory changes but no perivascular inflammation. The clinical and biochemical tests were noncontributory and there was no evidence for collagen disease. No cortisone was given because of the minor degree of the postinfectious myopathy. The symptoms completely regressed within ten months.