Adult idiopathic polymyositis without elevation of creatine kinase. Case report and review of the literature.

A patient fulfilling diagnostic criteria for definite polymyositis, but with normal levels of creatine kinase (CK) is reported. Review of the literature reveals significant variations regarding the frequencies of normal CK reported among cases with myositis. The discrepancies may be partly explained by inclusion of both probable and possible polymyositis, administration of steroid therapy prior to estimations of CK, and possible differences in CK levels between polymyositis and dermatomyositis. The patient reported did not suffer from neither lung disease nor concomitant malignancy. Thus, the alleged association between low levels of CK and poor prognosis in myositis could not be supported by the present case report.