Disease-specific and generic health outcomes: a model for the evaluation of long-term intrathecal opioid therapy in noncancer low back pain patients.

OBJECTIVE: The present study provided comprehensive characterization of the long-term outcomes of intrathecal opioid administration via a drug administration system (DAS) in chronic pain patients with predominantly low back pain. A conceptual framework based on multidimensional outcomes is proposed using both disease-specific and generic measures.

DESIGN: Pre-post longitudinal data were collected in a retrospective fashion on 38 patients receiving intraspinal opioid therapy for a minimum of 36 months (average = 50 months).

MAIN OUTCOME MEASURES: Disease-specific measures included magnitude of infused opioid, side effects/complications, pain ratings, McGill Pain Questionnaire, Beck Depression Inventory, Oswestry Disability Questionnaire, and patient estimated improvement in pain (0-100%). Generic measures of health included the Quality of Well-Being Scale, Medical Outcomes Study (MOS) Short Form 36 (SF-36), return to work, patient estimated improvement in functioning, overall patient satisfaction, and family opinion of patient improvement.

RESULTS: Disease-specific outcomes. Patients receiving long-term intrathecal opioid administration showed a sixfold increase in morphine equivalents infusion rates across time. DAS patients showed a small but significant decrease in pain ratings from pre-treatment levels. Following 3 years or more of intrathecal opioid infusion, patients endorsed high pain levels on the McGill Pain Questionnaire, severe levels of disability via the Oswestry Disability Questionnaire, mild levels of depression based on the Beck Depression Inventory, and multiple side effects associated with the intrathecal opioids and complications related to the infusion system. On retrospective questioning, patients receiving long-term intrathecal opioid administration reported an average of 64% improvement in their pain and 48% improvement in functioning. Family members of patients reported that they observed on average a 61% improvement in patient's pain. Generic outcome measures. On the Quality of Well-Being Scale, patients reported significantly lower health-related quality of life than health maintenance organization enrollees with no known chronic condition and patients with rheumatoid arthritis (p < 0.001). On the MOS SF-36, patients reported significantly lower physical functioning than the U.S. general population, patients with uncomplicated medical conditions, diabetes-type II patients, and congestive heart failure patients. Mental functioning was comparable to the U.S. general population (p > 0.001). Fourteen percent of patients were working following implantation. Eighty-nine percent of patients reported good to excellent satisfaction with the long-term intrathecal opioid therapy.

CONCLUSIONS: Results from this study revealed differences in findings across the outcome measures, highlighting the complexity of intrathecal opioid therapy. Generally, patients after 3 years or more of intrathecal opioid therapy can be characterized as hav ing substantially impaired physical functioning with a high prevalence of side effects. Despite poor physical functioning, patients endorsed relatively good mental health status with only mild depressive symptoms. Longitudinal pain ratings showed a modest decrease from pretreatment levels. On retrospective evaluation, patients and their family endorsed high levels of pain relief secondary to intrathecal therapy. Overall, findings support that intrathecal opioid therapy provides some therapeutic benefit although substantial physical impairment continues to cause debilitation in the patient population.