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Association between centralization, depression, somatization, and disability among patients with nonspecific low back pain.

STUDY DESIGN
Secondary analysis of a prospective observational cohort study.


OBJECTIVES
To evaluate whether depression and somatization subscores of the Symptom Checklist-90-Revised (SCL-90-R), which have been shown to identify chronic disability in individuals with nonspecific low back pain, are applicable to a different population of individuals with low back pain; and to determine if this potential association is confounded by a combination of centralization and subsequent treatment based on centralization.


BACKGROUND
To help direct management of patients with nonspecific low back pain, recommendations include performing tests designed to identify psychosocial risk factors predictive of poor patient outcomes. SCL-90-R depression and somatization subscores have been shown to predict chronic disability among patients with low back pain.


METHODS
SCL-90-R depression and somatization subscores and data on centralization were collected during the initial physical therapy examination of 231 consecutive patients treated for low back pain in 2 clinics. Disability was assessed by the Oswestry Disability Questionnaire at intake and discharge from physical therapy, and work status was determined by patient self-report at 6 and 12 months after discharge. Pain intensity was assessed by the numeric pain rating scale at the initial visit, and at 6- and 12-month follow-ups. Data were analyzed using logistic regression.


RESULTS
Odds ratios for the association between depression and somatization subscores and patient outcomes ranged from 0.76 to 2.93. For analyses in which the data suggested a trend toward an association, the association was less evident following adjustment for centralization and centralization-based treatment.


CONCLUSIONS
In our sample, in which all individuals received physical therapy, and those who centralized received interventions based on the direction of centralization, SCL-90-R depression and somatization subscores were moderately associated with chronic pain and disability. This association was reduced when centralization and centralization-based treatment was considered in multivariable analyses.