Discriminant validity and relative precision for classifying patients with nonspecific neck and back pain by anatomic pain patterns

Study Design. Secondary analysis of a previously described cohort of prospective, consecutive patients with acute neck or low back pain referred to outpatient rehabilitation was performed. Objective. To estimate discriminant validity and relative precision of two classification procedures (first visit vs multiple visit) in discriminating short-term pain intensity and perceived disability outcomes. Summary of Background Data. Centralization and noncentralization are pain responses used to classify patients and predict outcomes. Different time frames have been proposed for operationally defining these responses, which are problematic for comparing outcomes across clinical trials. Classifying patients according to pain response observed from initial examination (first visit) and overtime (multiple visits) influences prevalence within categories and interpretation of classification usefulness, which merits further investigation. Methods. Patients with acute onset of nonspecific neck or low back pain referred to two outpatient physical therapy clinics completed body pain diagrams, pain intensity ratings, and disability questionnaires at initial evaluation, during each visit, and at discharge. Therapists collected data enabling patient classification on initial examination and throughout treatment. Differences in pain and disability from intake to discharge from rehabilitation across classification categories were used to assess discriminant validity. Relative precision was estimated by determining ratios of analysis of covariance F values between classification procedures for pain and disability. Results. Both classification procedures discriminated categories for change in pain and disability. The multiple-visit classification procedure was more precise for discriminating outcomes than the first-visit classification procedure. Conclusion. Multiple-visit classification of patients into specific pain pattern subgroups is recommended when pain intensity and disability outcomes are of interest.