To compare the performance of a simplified scoring method for structural damage on radiographs of patients with rheumatoid arthritis (the Simple Erosion Narrowing Score or SENS) with the Sharp-van der Heijde Score (SHS) as reference.
We used the radiographic data from the Trial of Etanercept and Methotrexate with Radiographic Patient Outcomes (TEMPO trial). The SENS was derived from the crude SHS data. Inter-observer reliability for status scores and change scores was determined by intraclass correlation coefficients and by the Smallest Detectable Change method. The ability to discriminate between treatment groups was assessed by the Mann-Whitney U test. Stratifying the sensitivity to change and discriminative ability for different levels of disease severity assessed a potential ceiling effect.
Inter-observer reliability was similar for both methods. Intraclass correlation coefficients were higher for status scores than for change scores. The Smallest Detectable Change was 4.98 (1.1% of possible maximum score) for SHS and 2.28 (3.5%) for SENS. Sensitivity of SENS to detect progression above the Smallest Detectable Change, with reference SHS, ranged from 45.0 to 88.7%. Specificity ranged from 81.5 to 97.3%, and the kappa coefficient (between-method agreement) ranged from 0.58 to 0.66. Discriminative ability between treatment groups was good and similar for both methods. A ceiling effect could not be detected.
With regard to most of the tested properties, the performance of SENS is as good as that of SHS. This confirms that SENS is a valuable method, which may be feasible in clinical practice.