Rheumatoid arthritis is a systemic inflammatory disease with predominant involvement of the synovial joints.1 The current therapeutic focus in the management of RA is to reduce the overall inflammatory burden and to keep the synovitis as low as possible and to reduce the impact of the disease on overall morbidity and improve the quality of life.2 Early introduction of Disease Modifying anti-rheumatic drug (DMARD), good compliance, appropriate follow-up with continued disease activity measures to maintain a tight control of the disease will improve the out-come.3, 4, 5, 6 In our previous publication when we attempted to analyze the role played by various core set criteria on the measure of change in a patient of RA, three parameters like Swollen joint count (SJC), Visual analogue scale (VAS) pain scale and a measure of inflammation (ESR) had a greater influence on changes observed on feeling of improvement from both patients as well from physician point of view.
7 Recent publications suggest that a significant difference can be observed in disease activity of RA by use of clinical measures between active drug and controls even, without the use of laboratory inflammatory parameters such as ESR and CRP.
8 However contrary to this, there are multiple studies which suggest that laboratory inflammatory parameters like ESR and CRP serve as more useful predictor for disease outcome variables such as joints erosion; and inflammatory parameters have stronger correlation than clinical variables such as Tender joint count (TJC) and SJC.9, 10, 11 With the current understanding of the disease process, it is clear that the key to successful management of RA is to reduce the inflammation to minimum and thereby reduce the impact of the disease.9, 12 The variables like TJC, SJC, pain measures and physician and patients assessment closely reflect the clinical manifestations of the inflammatory process and may not be reflect the burden of inflammation in totality. In addition the evaluation of TJC and SJC is time consuming and often influenced by observers bias.13 Observable difference exists even when DAS is calculated based on ESR and CRP. However, Cynthia et al8 argue with elegant demonstration that well measured CRP should be a reasonable good marker in the follow-up of an RA patient in day to day clinical practice.
The question that arises is which of these inflammatory parameters should be preferred to use. Cheaper establishment (or Cost factors), general availability and reasonable association with other disease parameters make the case for ESR against CRP, though several studies have suggested CRP to be superior to ESR.8 Most of these studies have attempted to correlate the measures which suggest a possible relationship between the parameters rather than their overlapping powers. Correlation depends on the range of the true quantity in the sample.14 The test of significance by correlation may show that the two methods are related, but not overlapping or can replace one with other.15 In this study we have attempted to see how much agreement occurs as a measure for inflammation between these clinical variables such as TJC, SJC and VAS scale and the laboratory inflammatory variables ESR and CRP by mountain plot analysis.16 We hypothesize that, as a measure, CRP supersedes ESR in its power to replace other clinical measure. This study was undertaken to find out how much ESR and CRP as test parameters, overlap with the TJC, SJC and VAS pain scale in a routine clinical practice.
ESR and CRP are two commonly used laboratory inflammatory parameters. The controversy remains which of the two is a better measure to use and which parameter closely reflects the clinical measures of inflammation as well the disease process in Rheumatoid arthritis.
We used mountain plot analysis to find out the congruency of ESR and CRP individually with clinical measures namely Tender joint count (TJC), Swollen joint count (SJC) and Visual analogue scale for Pain (VAS). 303 RA patients who are in our regular follow-up were included in the study. There TJC, SJC and VAS pain and ESR and CRP were retrieved.
242 were female and 61 were male patients. The mean age was 46.8 years (17-79 years), mean duration of illness was 70.81 (3-307) months. All of them were on conventional DMARD with majority on combination of methotrexate, Hydroxychloroquine and/or leflunomide. Both ESR and CRP correlated with all three measures such as TJC, SJC and VAS. The correlation was stronger with ESR than CRP. When the effectiveness of ESR vs CRP was compared for their overlapping on the clinical parameters TJC, SJC and VAS by using mountain plot method, CRP performed better than ESR and coincided with all three clinical parameters of the disease RA.
Our study emphasizes the fact that CRP is a better measure of inflammation than ESR and represents the information on the inflammatory component provided by both TJC and SJC, as appreciated by the close overlap. The CRP can replace the clinical measures (joint counts and Pain scale) more effectively than ESR, provided other causes for elevation of CRP are excluded.