Cross-validation of the Back Pain Classification Scale with chronic, intractable pain patients.

The current study investigated the utility of the Back Pain Classification Scale with chronic, intractable low back pain and headache patients. Subjects consisted of 50 chronic low back pain and 50 chronic headache patients referred to a university based Pain Center for evaluation. Data indicated that subjects were a representative sample of severely intractable chronic pain patients typically referred for Pain Center evaluation and treatment. Each was administered the Back Pain Classification Scale as part of a thorough physical and psychological/behavioral evaluation. All subjects were classified by blind review of medical records into one of two categories: (1) presence of psychopathologically based pain complaint with little or no pathophysiological findings and (2) presence of pathophysiologically based pain complaints with little or no psychopathological findings. Subjects were also independently classified from blind review of their scores on the Back Pain Classification Scale into one of these two categories. Findings revealed that the Back Pain Classification Scale accurately predicted the actual classification of 80% of the low back pain patients (i.e., 30% above baseline prediction rate) and only 60% of the chronic headache patients (i.e., only equal to the baseline prediction rate). Furthermore, the scale was found to be most accurate in predicting low back pain patients with primary psychopathologically based pain. It was concluded that the Back Pain Classification Scale was an empirically valid instrument to use with chronic low back pain patients, but not with chronic headache patients. This lack of utility with chronic headache patients was also viewed as support for the construct validity of the scale. Wider use of the scale with chronic low back pain patients was suggested.