The concept of the primary myopathies is, as yet, not firmly established, and the characteristics of the various groups of muscular dystrophies are not universally delineated. The many etiologic factors have been debated but have remained obscure and, therefore, no rational therapy can be advocated. The contractile processes in the muscles, whether they are of metabolic or of neurogenic nature, have kept physiologists and biochemists busy, and the investigations have resulted finally in the Hill-Meyerhof formulation, which, unfortunately, does not explain the problem of muscular fatigue.
The differential diagnosis between primary and secondary myopathies is clinically difficult and, we believe, at times impossible without the estimation of creatine and creatinine. Whereas the primary myopathies are accompanied by alterations in the metabolic creatine, the secondary myopathies are not associated with such changes. Important points in the differential diagnosis are heredity, age, electrical reactions, pathologic changes observed at biopsies of muscles, and