Simplified Larsen erosion score (SLES) for estimating joint damage in early rheumatoid arthritis in clinical practice

Rheumatoid arthritis (RA) is a chronic inflammatory disease that, untreated, often leads to joint damage, which may lead to functional impairment and disability. Radiology is still the gold standard for evaluating joint damage in patients with RA and is often used as an outcome measure in clinical trials to assess structural damage of the hands and feet (1–3). Early individual treatment to prevent joint damage is decisive for the outcome. For this purpose, a practical tool for evaluating radiological damage in clinical practice is needed. The scoring methods according to Larsen (4) and Sharp van der Heijde (5), the most used methods in clinical trials, are very time consuming and require experienced readers. For the Sharp van der Heijde score (SvHS), a simplified erosion narrowing score (SENS) exists and has been shown to be as good as the SvHS regarding reliability and sensitivity (6). SENS has also been evaluated for use in clinical practice (7). The Larsen score, like the SvHS, is a time-consuming method, and there is a need in clinical practice for a simplified tool. Therefore, we studied whether a simplification of the Larsen score, just assessing erosions (present or not in the same locations), could give the same clinical information regarding change in joint damage in early RA as the Larsen score. The simplified Larsen erosion score (SLES) evaluates the same 32 locations as the Larsen score for the presence (1) or absence (0) of erosions. The Larsen score range is 0–160, whereas the SLES range is 0–32. In a cohort of 217 patients diagnosed with early RA (disease duration < 12 months) from the Swedish TIRA-2 study (Swedish acronym for ‘Early Intervention in Rheumatoid Arthritis’, for which the material has previously been described in detail) (8), we evaluated the SLES, which was derived from the Larsen scores in 217, 155, 119, and 162 patients at inclusion (baseline), 1, 2, and 3 years follow-up, respectively. Both the SLES and the Larsen score showed very good intraobserver reliability by the intraclass correlation coefficient (ICC = 0.961 and 0.974, respectively). The interobserver reliability for the Larsen score was ICC = 0.903. Radiographic progression was defined as a difference in Larsen score above the smallest detectable change (SDC), according to the method of Bruynesteyn et al (9), and was calculated as 3. Table 1 compares joint damage in patients with and without radiographic progression at different time points, assessed by the SLES and Larsen score. The progression of joint damage over 3 years, by the SLES and Larsen score, at inclusion and after 1, 2, and 3 years is presented in Figure 1. The SLES correlated significantly with Larsen scores at all time points (correlation coefficients 0.433–0.496; p < 0.001). A higher correlation was observed in radiographic progression over 36 months (0.643; p < 0.001). Comparing only erosions of the Larsen score with SLES separately, an even higher correlation coefficient was seen (0.993–0.998; p < 0.001). The same grade of correlations was found with radiographic increase and decrease in joint damage. The sensitivity of SLES to detect progression from baseline to 3 years, with progression by Larsen score above the SDC as the reference, was 61.3%. The