Predicting Response to Subacromial Injections and Lidocaine/Tetracaine Patch from Pretreatment Pain Quality in Patients with Shoulder Impingement Syndrome.

OBJECTIVES: No existing pain treatment is effective for all pain problems, and response to pain treatment is highly variable. Knowledge regarding the patient factors that predict response to different treatments could benefit patients by providing an empirical foundation for patient-treatment matching. This study sought to test the hypothesis that improvements following two treatments thought to operate via similar mechanisms would be predicted by similar baseline pain qualities. DESIGN: Prospective prediction analysis using data from a previously published open label trial comparing a heated lidocaine/tetracaine patch versus subacromial corticosteroid injection for the treatment of pain in individuals with shoulder impingement syndrome. RESULTS: Consistent with the study hypothesis, the response to the two treatments were predicted by similar baseline pain qualities; specifically, higher baseline levels of unpleasant, electric, and sensitive pain predicted subsequent improvements in sleep interference, work/activity interference, and patient global ratings of improvement, respectively. CONCLUSIONS: The findings are consistent with the combined ideas that (1) those who have the most to gain (i.e., those reporting the highest levels of various pain qualities) can expect the best response to effective treatments and (2) different pain qualities may be associated with different types of outcomes. The findings support further research to examine how pain quality measures may be used to improve patient-treatment matching, and therefore, ultimately improve the efficiency, efficacy, and overall benefit-risk of pain treatment.