Cross-validation of the back pain classification scale with chronic, intractable pain patients

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Abstract
The utility of the Back Pain Classification Scale was investigated 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. 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 1 of 2 categories: presence of psychopathologically based pain complaint with little or no pathophysiological findings and 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 1 of these 2 categories. 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). The scale was most accurate in predicting low back pain patients with primary psychopathologically based pain. The Back Pain Classification Scale was evidently 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.