Serum ATP level: a useful measure for fatigue in patients with rheumatoid arthritis

ABSTRACT

Fatigue is a frequently occurring symptom in individuals with rheumatic diseases, including rheumatoid arthritis [RA], and contributes to many disabilities in those patients. Several variables acting singly or in combination may contribute to the mechanism of this fatigue. The end result of these factors is the depletion of intracellular and extracellular adenosine triphosphate [ATP]. This study was conducted to assess ATP levels in patients with active and inactive RA, and its correlation to fatigue. Forty-two RA patients were chosen from the outpatient clinics of Al-Azhar University Hospitals, over two years duration [1999-2000]. Patients with suspected or evidenced to have myositis, or under corticosteroid therapy were excluded from the study. The patients were classified into two groups active RA [22 patients], and inactive RA [20 patients]. Another group of 20 normal volunteer subjects was selected as a control group. RA disease activity, the short-form McGill Pain Questionnaire including visual pain analogue scale [VAS], Ritchie's articular index, early morning stiffness, fatigue visual analogue scale [FVAS], and routine laboratory tests were all measured. Serum ATP was measured by modified enzymatic UV test. Early morning stiffness, Ritchie's articular index, hemoglobin level, pain score, and erythrocyte sedimentation rate, were all increased significantly in active and inactive RA than controls, and were not correlated to fatigue. Serum ATP level was significantly lowered in active than inactive RA and controls, while it was not significantly different between inactive RA and normal controls, and it was highly significantly inversely correlated to fatigue as measured by the fatigue- visual analogue scale. The overall outcome of fatigue processes is the depletion of ATP stores, with resultant lowered intracellular and extracellular levels of ATP. Serum ATP level was the only reliable and precise factor for measuring fatigue in RA patients