Comprehensive assessment of rheumatoid hand using cluster analysis involving parameter analysis of three major hand deformities: a cross-sectional and longitudinal study

Abstract Background Although drug therapy in rheumatoid arthritis has recently improved, treating established rheumatoid hand consisting of three major deformities—thumb deformity, finger deformities, and ulnar drift—remains a challenge. Underlying complex pathophysiology makes it difficult to comprehensively understand these deformities, and comprehensive assessment methods require accumulated skill and long learning curves. We aimed to establish an easier composite method of understanding the pathophysiology using data from our cohort and cluster analysis. Methods We established a rheumatoid hand cohort in 2004, and clinically evaluated 134 hands (67 patients). We repeated the evaluations in 2009 and 2015, which provided data for 297 hands and 43 hands for cross-sectional and longitudinal analyses, respectively. Thumb deformities, finger deformities (swan-neck and boutonnière deformity), and ulnar drift were semi-quantified and entered as parameters into a two-step cluster (cross-sectional) analysis. Parameter distributions were considered to clarify each cluster’s characteristics. Next, hands with cluster change over the study period were reviewed to clarify deformity progression (longitudinal analysis). We also performed a stratified analysis between the clusters and the affected period to clarify whether long affected period plays an important role in deformity progression. Results We identified seven clusters: cluster 1: mild finger deformities; cluster 2: type 1 thumb deformity; cluster 3: type 2 thumb deformity and severe ulnar drift; cluster 4: type 3 or 4 thumb deformity and low or moderate swan-neck deformity; cluster 5: various thumb deformities and severe boutonnière deformity; cluster 6: type 1 thumb deformity and severe swan-neck deformity; and cluster 7: type 6 thumb deformity. The ulnar drift parameters were equally distributed among the clusters except for cluster 3. Larger cluster numbers generally indicated lower function. At the study endpoint, cluster 1 had changed mainly to cluster 2 or 4, cluster 2 changed to cluster 3, and cluster 7 was considered the final morphology with the lowest hand function. Patients affected for > 30 years had increased risk of rapid disability progression. Conclusions Our comprehensive assessment indicated seven deformity patterns and a progressive course in rheumatoid hand. Using patterns may provide rheumatologists with easier information for practical interventions and to determine functional prognosis.