Psychologic classification of low-back pain patients: a prognostic tool.

The Pain Drawing Test and Back Pain Classification Scale (BPCS) were examined for their degree of correspondence in measuring psychologic disturbance and for their value in predicting treatment outcome in four areas: medication need, work status, patients' rating of improvement, and change in pain over a 12-month period. Agreement between the two measures in identifying patients as "not psychologically disturbed" was good; agreement was far less for patients identified as "psychologically disturbed." At the same time, both measures predicted clinical outcome with an equal degree of accuracy across the measures of outcome, except for "return-to-work status" where significant group trends with the BPCS did not reach significance with the Pain Drawing Test. The strong correlation between the two measures in predicting clinically important indexes of improvement suggests that differences in diagnosing the psychologically disturbed does not represent error. The difference may arise because the two scales tap different aspects of psychologic disturbance. Both scales appear to be of clinical value in the early identification of probable treatment failures.