Comprehensive assessment of alterations in hand deformities over 11 years in patients with rheumatoid arthritis using cluster analysis and analysis of covariance

Background Although drug therapy for rheumatoid arthritis (RA) has recently improved, treating patients with established disease, whose hands have three major deformities (thumb deformity, finger deformities, and ulnar drift), remains a challenge. The underlying complex pathophysiology makes understanding these deformities difficult, and comprehensive assessment methods require accumulated skill with long learning curves. We aimed to establish a simpler composite method to understand the pathophysiology of and alterations in the hand deformities of patients with RA. Methods We established a rheumatoid hand cohort in 2004 and clinically evaluated 134 hands (67 patients). We repeated the evaluations in 2009 (100 hands of 52 patients) and 2015 (63 hands of 37 patients) after case exclusion. Thumb deformities, finger deformities (swan-neck and boutonnière deformity), and ulnar drift were semi-quantitated and entered as parameters into a two-step cross-sectional cluster analysis for the data in 2004. The parameters in each cluster were plotted at each evaluation point. Two-way analysis of covariance was used to examine whether differences existed between evaluation points and clusters of deformity parameters. Results Five clusters most appropriately described hand deformity: (i) cluster 1, minimal deformity; (ii) cluster 2, type 1 thumb deformity; (iii) cluster 3, thumb deformity and severe boutonnière deformity; (iv) cluster 4, type 2 or 3 thumb deformity and severe ulnar drift; and (v) cluster 5, thumb deformity and severe swan-neck deformity. Clusters 1 and 2 had higher function than cluster 5, and cluster 3 had moderate function. Clusters 1–4 had similar disease duration but showed different paths of deformity progression from disease onset. Clusters 1 and 2 represented conservative deformity parameters and clusters 3, 4, and 5 represented progressive deformity parameters. Over time, thumb deformity evolved into other types of deformities and swan-neck deformity worsened significantly. Conclusions Our comprehensive analysis identified five deformity patterns and a progressive course in the rheumatoid hand. Knowledge of the characteristics of progressive deformity parameters may allow rheumatologists to more easily implement practical interventions and determine functional prognosis.