Botulinum toxin effective for tennis elbow pain

The toxin’s paralytic effect may force extensor muscles to rest, allowing tendon fibers time to repair.

Botulinum toxin may offer a possible alternative short-term treatment for patients with lateral epicondylitis, according to a study by Hong Kong researchers.

Shiu Man Wong, MB, BCh, and colleagues at the North District Hospital and at the Prince of Wales Hospital, randomly assigned 60 patients to undergo injections of either Dysport (botulinum toxin, Beaufour Ipsen International) or normal saline solution. All patients had lateral elbow pain that had persisted for more than three months and lateral epicondyle pain during resisted wrist dorsiflexion with the elbow fully extended, according to the study.

Investigators injected either 60 units of botulinum toxin or saline deep into subcutaneous tissue and muscle approximately 1 cm from the lateral epicondyle. All injections were aimed toward the point of tenderness, the authors noted.

The researchers instructed all patients to avoid pain-provoking activities for 48 hours after injection. Patients were also told to stop any other treatments, such as NSAIDs and physical therapy, for the 12 weeks’ follow-up.

“Our findings suggested that botulinum toxin injection was superior to placebo for reducing pain over a 12-week period ...,” the authors said in the study.

At four weeks, botulinum toxin patients had a statistically significant improvement in pain, measured using the Visual Analog Scale (VAS), compared to placebo patients (P<.001). The difference was maintained at 12 weeks (P<.006), according to the study.

Mean VAS pain scores improved from 65.5 mm at baseline to 25.3 mm at four weeks and to 23.5 mm at 12 weeks for botulinum toxin patients. For placebo patients, mean VAS scores improved from 66.2 mm at baseline to 50.5 mm at four weeks and to 43.5 mm at 12 weeks, according to the study.

Grip strength remained similar between groups. Patients treated with botulinum toxin had a higher incidence of adverse effects, however.

At four weeks, 10 botulinum toxin patients and six placebo patients had mild finger extension weakness in the injected arm. This weakness persisted at 12 weeks in two botulinum patients and one placebo patient. Additionally, at four weeks, four botulinum toxin patients, but no placebo patients, had paresis of their second and fourth digits.

Two botulinum toxin and one placebo patient also had mild post-injection pain that lasted up to two weeks, according to the study.

The authors speculated that the toxin injections worked due to the toxin's paralytic effect. The paralysis may force the extensor muscles to rest for up to four months, allowing tendon fibers time to repair, according to the study.

For more information:
Wong SM, Hui ACF, Tong P, et al. Treatment of lateral epicondylitis with botulinum toxin. Ann Intern Med. 2005;143:793-797.