The childhood arthritis radiographic score of the hip: the proposal cut-off value using cluster analysis

Background Juvenile idiopathic arthritis (JIA) is a chronic rheumatic disease that affects children. It is crucial to detect and treat hip involvement in JIA early to prevent functional impairment and reduced quality of life. The Childhood Arthritis Radiographic Score of the Hip (CARSH) is a validated radiographic scoring system used to assess hip involvement in JIA. In this study, we aimed to determine cut-off values for CARSH scores using cluster analysis. Methods The study was conducted as a cross-sectional analysis and included JIA patients with hip involvement who underwent a pelvic radiograph. The same pelvic radiograph was interpreted by two experienced pediatric rheumatologists at baseline and after 3 weeks by both readers for reliability. The CARSH scores were calculated for each hip four times (twice by each reader). For the 50 hips, a total of 200 interpretations of the CARSH score were obtained. Model-based clustering was employed to identify distinct groups of CARSH score interpretations and characterize the phenotype of each cluster. Results Twenty-five children with hip involvement were included. The mean age was 13.9 ± 4.6 years. JIA subtypes were as follows: ERA in 64%, oligoarthritis in 16%, psoriatic arthritis in 12%, polyarthritis RF + in 4%, and RF − in 4% of patients. For the 200 hip interpretations, three clusters based on the level of the CARSH were identified by model-based clustering. Cluster 1 consisted of 17 CARSH score interpretations with a median score of 7 ± 3 (ranging from 1 to 15). This group primarily comprised patients with enthesitis-related arthritis (ERA) and psoriatic arthritis. Patients in cluster 1 were generally older, experienced longer diagnostic delays, and had a longer disease duration compared to the other clusters. Cluster 2 exhibited a moderate CARSH score, with an average score of 4 ± 3 (1 to 15). Patients in this group had significantly higher body weight compared to the other clusters. Cluster 3 represented the group with the least severe hip involvement, characterized by CARSH scores of 2 ± 1 (ranging from 0 to 9). This cluster had a higher proportion of male patients and higher C-reactive protein (CRP) levels than the other clusters. Regarding the individual items of the CARSH score, cluster 1 showed higher percentages of hip radiograph abnormalities such as joint space narrowing, erosions, growth abnormalities, and subchondral cysts. Cluster 2 was characterized by a high rate of acetabular sclerosis, with little to no abnormalities in other CARSH score items. Cluster 3 was the only group that exhibited hip subluxation, with minimal abnormalities in the other score items. In conclusion, this study identified three distinct groups of CARSH scores, representing varying levels of severity in hip involvement in JIA. These findings provide valuable insights for clinicians in assessing and managing JIA patients with hip involvement, enabling tailored treatment strategies based on the severity of the condition. Key Points • While a Childhood Arthritis Radiographic Score of the Hip (CARSH) is a valid and reliable tool in hip-related juvenile idiopathic arthritis, its use is limited in daily practice due to the lack of available cut-off values. • The cluster analysis defined three clusters based on the CARSH levels. • Cluster 1 exhibited the highest score with more damage and disability. Cluster 2 involved a moderate score and more overweight patients. Cluster 3 included the least level of the score but with an active disease parameter.