Chronic back pain: electromyographic, motion and behavioral assessments following sympathetic nerve blocks and placebos.

Twenty patients with chronic low back pain received 12 lumbar sympathetic injections, in a series of 6 with bupivacaine and a series of 6 with saline. Changes in subjective pain intensity, EMG from paravertebral muscles, joint ranges of mobility, and daily activity levels were measured at multiple intervals throughout treatment and at 3 monthly follow-up intervals. The MMPI was administered before treatment, after treatment and at 3-month follow-up. Results revealed significant reductions in subjective pain intensity lasting 1 month after treatment which were not significantly different during bupivacaine and saline injection periods. Patients' MMPI profiles were indicative of reduced depression and an increase in ability to manage their lives. No significant changes were recorded with respect to EMG, joint range of mobility, or daily activity levels. Results were discussed in terms of a massive placebo effect and analgesia obtained through hyperstimulation of various tissue structures. They are consistent with the hypothesis that central postsynaptic mechanisms were predominant in these patients' chronic back pain states. Because subjective pain relief did not independently produce increasing function, it was recommended that deep analgesic injections or other pain relieving techniques be matched with behavior modification leading to functional rehabilitation.