British Journal of Rheumatology 1994;33:231-234 REDUCED ACTIVITY OF SERUM CREATTNE KINASE IN RHEUMATOID ARTHRITIS: A PHENOMENON LINKED TO THE INFLAMMATORY RESPONSE

In a case-controlled study, serum creatine kinase (CK) activity was significantly lower in 40 patients with RA than in 40 age- and sex-matched patients with non-inflammatory arthropathies [mean 37.6 (S.D. 29.2) vs 77.7 (S.D. 45.3) IU/1 respect-ively P<0.0001]. In contrast, serum levels of aldolase and myosin were not significantly lower in RA patients. A significant inverse correlation between CK activity and ESR, CRP and platelet count was observed in RA. There was also a positive correlation between haemoglobin levels and CK values. No correlation was found between CK activity and a meager mass index, disease duration and radiological erosion. No inhibitor of CK activity in the sera of RA patients was found. CK serum activity was markedly reduced in RA, and is related to the inflammatory activity of the disease. This finding may stimulate further exploration on the effect of inflammatory response in muscle metabolism. KEY WORDS: Serum creatine kinase, Rheumatoid arthritis, Inflammatory response, Disease activity, Rheumatoid myositis. CREATINE kinase (CK) (EC 2.7.3.2) is the serum enzyme most frequently used in the diagnosis and management of muscular diseases. Activity of serum CK is raised in different myopathies such as muscular dystrophies and inflammatory myopathies. It is note-worthy that little attention has been paid to the decreased activity of this enzyme in medical practice. When routinely analysing serum CK activity in RA, we have observed that most patients exhibited a serum CK activity below our normal laboratory limit. In order to confirm this finding and to establish its relationship with the activity and severity of the disease, a case-controlled study was performed. PATIENTS AND METHODS Forty consecutive outpatients (29 female) with clas-sic or definite RA, according to ARA criteria (1987), seen in the Rheumatology Services of the Hospita