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Am Fam Physician. 2001;64(12):2004-2005

Back pain is among the most common reasons for patients to seek health care, costing the American economy approximately $50 billion a year. Frequently used pharmacologic therapies include nonsteroidal anti-inflammatory medications, muscle relaxants, opioids and other analgesics, and antidepressants. In patients with chronic pain, the majority of these treatments fail to provide complete, lasting relief. Intramuscular injection of botulinum toxin has been used for a variety of disorders. Given that chronic back pain often has a component of muscular spasm, it seems worthwhile to consider the role of botulinum toxin in the treatment of this disorder. Foster and associates performed a randomized, double-blind study to assess the efficacy of botulinum toxin in patients with chronic low back pain.

In this study, 31 eligible patients had low back pain for at least six months' duration. Patients were excluded if they were younger than 18 years, had a known systemic inflammatory disorder, significant acute findings on a magnetic resonance image, or recent injection of a corticosteroid. All patients rated their level of back pain using a 10-point visual analog scale (rated from “no pain” to “worst pain”) and a standardized questionnaire to assess the degree of physical impairment (tasks of daily living, including grooming, lifting, walking, sitting, standing, and sleeping). Forty units of botulinum toxin or an equivalent volume of saline were injected into five lumbar or lumbosacral sites. The physician and patient were blinded to the content of the injection. Scores were assessed again three and eight weeks after treatment.

The average patient age was 46 years, and patients had pain for approximately six years. Men and women were equally distributed, and 28 patients completed the study. The mean initial rating of pain on the 10-point scale for both groups was seven. At three weeks, 13 of 15 patients in the treatment group and five of 16 patients in the placebo group reported some degree of pain relief. In 11 patients in the treatment group, the visual analog score decreased by more than 50 percent compared with four patients in the placebo group. At eight weeks, nine of 15 patients in the botulinum toxin group and two of 16 patients in the saline group reported pain relief exceeding 50 percent. On the functional scale, similar improvements were reported. There were no reports of adverse side effects.

The authors conclude that paravertebral muscular injection with botulinum toxin in patients with chronic low back pain relieved pain and improved function at three and eight weeks after treatment. Further studies are needed to determine if these results can be reproduced in a larger number of patients and if this positive effect continues with repeat injections, as it does with dystonias and spasticity.

editor's note: This study shows a potential use for botulinum toxin in the management of patients with muscular back pain. The results should be interpreted with caution. First, this was a select group of patients with chronic back pain, many of whom had pain for several years and self-reported a high pre-injection level of pain. Second, patients did not obtain complete pain relief. Based on the presented results, the average patient still had mild to moderately intense post-treatment pain. Whether these results can be generalized to patients with acute back pain is also a question. Larger studies of similar methodology will be useful. Finally, it is important to comment on cost. A 100-unit vial of botulinum toxin costs $462 (personal communication from Allergan, Inc.; 800–530–6680). Given the use of 200 units per patient in this study, it seems that routine management of patients with this drug would be cost-prohibitive.—b.z.

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