Characteristics of pain–related factors in subgroups based on central sensitivity syndromes and pain in musculoskeletal pain patients: a cluster analysis

Central sensitization (CS) and psychological factors are associated with pain intensity. However, it has remained unclear whether the effects of central sensitivity syndromes and cognitive ⁄ emotional factors differ depending on the severity of pain and the pain quality. Our purposes were to perform subgrouping based on central sensitivity syndromes and pain intensity, and to clarify the difference in central sensitization syndrome and pain intensity between subgroups. Fifty–nine patients with musculoskeletal pain were included in this cross– sectional study. Pain intensity and psychological problems were assessed with Central sensitization inventory (CSI–9), Short–Form McGill Pain Questionnaire 2 (SFMPQ2), Hospital Anxiety and Depression Scale (HADS), Pain Catastrophizing Scale (PCS–4). The cluster analysis with a ward method was used to divide patients into subgroups based on central sensitization syndrome and pain intensity. In addition, Kruskal–Wallis test, multiple comparison (Bonferroni method), and Fisher’s exact test were performed to compare clinical outcomes between subgroups. The level of significance was set at 5%. The cluster analysis classified into three subgroups. One subgroup of patients (n=11) was characterized by high level of central sensitivity syndromes, pain intensity and psychological problems. A second subgroup (n=19) was characterized by low level of central sensitivity syndromes, moderate level of pain intensity, high level of psychological problems. The third subgroup (n=29) was characterized by low level of central sensitivity syndromes, pain intensity and psychological problems. That is, one subgroup was mainly affected with central sensitivity syndromes, and another subgroup was affected psychological factors. These results indicated the differences in pain mechanism among subgroups.