Utility of the MMPI Pain Assessment Index in predicting outcome after lumbar surgery.

A Pain Assessment Index (PAI), computed from a weighted combination of MMPI scales scores, has been developed to assess a pain patient's tendency toward continued pain complaints after surgery (Smith & Duerksen, 1979). This study examined the ability of the PAI, determined from presurgery MMPIs, to predict outcome subsequent to lumbar laminectomy and discectomy. One hundred and six chronic low back pain patients (61 males, 45 females) were categorized as having good, fair, or poor outcome 1 year or more postsurgery. Using the cutting score proposed by Smith and Duerksen (1979), the PAI correctly classified 79% of the subjects as having good or fair/poor outcome, and 87% as to whether they were working at follow-up. However, the MMPI Hypochondriasis (HS) scale alone correctly predicted the overall outcome of 83% and the work status of 81% of the subjects. The PAI (and, to a lesser extent, the HS and Hysteria [HY] scales of the MMPI) were found to have good ability to identify patients who were doing well after surgery, but low power in predicting which patients would have a fair or poor surgical result.