Diagnostic and Activity Criteria of Rheumatoid Arthritis Evaluated with Factor Analysis

Abstract

Factor analysis was used to characterize the diagnostic criteria of rheumatoid arthritis in a follow-up study of a population sample and to find economic criteria for measuring the activity of rheumatic inflammation in a longitudinal evaluation of hospital patients. Six factors were considered significant in the population series: nonremitting rheumatoid arthritis, “falsely” positive RF reactions, remitting clinical polyarthritis, radiological RA age, morning stiffness - pain on motion, and non-specific inflammation in females. Thus many of the recognized dimensions of the rheumatic disease complex in the population were represented as factors, and the analysis suggested a new one (morning stiffness and pain on motion being constant during the observation period) which may serve as a working hypothesis for further studies. The analysis of the initial status in the hospital series revealed one factor reflecting inflammation as evidenced by laboratory tests; clinical features of the inflammation remained a separate entity, and one factor reflected RF activity. Changes in the status during the stay at the hospital were analysed in a systematic fashion. In addition to changes per se, more complex parameters were used by taking into account the initial status and/or the time period. Although the solutions differed markedly from each other, the study suggested some group factors (such as the combination of ESR and CRP) and some unique factors (e.g. leucocytosis) that may represent separate dimensions of the rheumatic inflammation.