Behavioral Symptom Clusters, Inflammation, and Quality of Life in Chronic Low Back Pain

Purpose of study: The purpose of this study was to identify behavioral symptom clusters (depressive mood, fatigue, poor sleep) in individuals with chronic low back pain (CLBP), and to determine whether there are differences in pain, quality of life (QOL) and inflammation (plasma IL-6) based on cluster membership.

Background and significance: CLBP is a prevalent condition, often involving an inflammatory process. Those with CLBP frequently report burdensome behavioral symptoms, including depressed mood, fatigue, and sleep disturbance, which may exacerbate pain and/or reduce QOL. Although symptom clusters have proved clinically useful in other patient populations (e.g., cancer, heart failure), no study has investigated behavioral symptom clusters in CLBP patients.

Methods: CLBP patients (N=69; age = 56±13 years) were enrolled from a pain clinic. Participants completed measures of pain severity and pain interference with activities, depressive mood, fatigue, sleep, and QOL; and provided blood for IL-6 measurement.

Analysis: Behavioral clusters were identified using latent class analysis (LCA). Univariate and regression models were used to determine differences between groups and whether behavioral symptoms and IL-6 predicted pain profiles and/or QOL. Models controlled for analgesic use or body mass index (BMI), as appropriate.

Results: Latent class analysis revealed a two-class model. Participants in Class 1 characterized by High Behavioral Symptoms (HBS) had more depressive mood, fatigue, and sleep disturbance (including less sleep per night) compared to participants in Class 2 characterized by Low Behavioral Symptoms (LBS). Univariate general linear models revealed HBS reported worse QOL and pain interference than those in LBS. Pain severity did not significantly differ between the classes. Exploratory analysis suggested this was due to a moderating effect of IL-6 on pain severity. Levels of IL-6 (controlling for BMI) were trending to significantly greater in HBS, compared to LBS, with higher levels of IL-6 correlating with greater pain severity and more sleep disturbance. Further, logistic regression revealed higher levels of IL-6 predicted HBS membership.

Conclusion and Implications: Behavioral symptoms cluster in those with CLBP and worsen QOL. Inflammation contributes to the complex relationship between behavioral symptoms and pain severity. Clinical recognition of behavioral symptom clusters can foster more comprehensive pain assessment and tailored interventions for CLBP patients.