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Botulinum toxin A injection may ease base-of-thumb osteoarthritis pain

Author: Claire Barnard

medwireNews: Intra-articular injection with botulinum toxin A results in clinically meaningful pain reduction for up to 3 months in people with base-of-thumb (trapeziometacarpal) osteoarthritis, French study findings indicate.

Christelle Nguyen (Centre-Université Paris Cité) and co-investigators say: “Botulinum toxin A could be considered as a fast-acting, intra-articular therapy targeting chronic pain” in these patients.

Nguyen and team carried out the single-center, phase 3 RHIBOT trial among 60 adults (mean age 64.9 years, 78% women) who fulfilled the 1990 American College of Rheumatology criteria for hand osteoarthritis with X-ray evidence of trapeziometacarpal osteoarthritis and a self-reported base-of-thumb pain intensity score of 30 points or more on a scale of 0–100 (mean score 60 points).

Half of the participants were randomly assigned to receive an ultrasound-guided injection of botulinum toxin A (50 Allergan units) in 1 mL of saline in the trapeziometacarpal joint and the other half received 1 mL of saline alone, both in addition to custom-made rigid splinting.

At 3 months post-treatment, individuals who received botulinum toxin A reported a mean 25.7-point reduction in base-of-thumb pain. The reduction was 9.7 points in the control group, resulting in a statistically significant and clinically meaningful absolute difference of 16.0 points (threshold for clinical significance=15.0 points), the researchers report in The Lancet Rheumatology.

The difference between the two groups was also significant by 1 month after injection, at 16.3 points, with mean reductions from baseline of 34.3 and 18.0 points in the experimental and control arms, respectively.

However, there was no significant difference in pain between the two groups at 6 months nor were there differences in other secondary outcomes, such as change in Cochin Hand Function Scale score and patient global assessment, OARSI-OMERACT response, and the use of analgesics or NSAIDs, at 3 or 6 months.

Adverse events were reported by 90% of participants who received botulinum toxin A and 80% of those who received placebo, most commonly base-of-thumb pain (20 vs 37%), thenar muscle motor deficit (47 vs 7%), and other musculoskeletal pain (17 vs 20%). There were no serious adverse events in either group and the investigators note that the thenar muscle deficit was mild and transient.

“This adverse event might be prevented by injecting a smaller volume or dose of botulinum toxin A, or both,” they remark.

Nguyen and co-authors conclude: “Future studies are needed to investigate the potential mechanism of the effects observed in this trial, to replicate our findings, and to assess the effects of repeated injections over time and their clinical effectiveness, including an analysis of cost-effectiveness.”

In an accompanying comment, Anna Døssing and Henning Bliddal, both from the University of Copenhagen in Denmark, say the study demonstrates that botulinum toxin A is a “clear short-term treatment option for patients with painful base-of-thumb osteoarthritis, a condition with limited treatment options.”

They point out, however, that the benefit “is restricted to pain reduction and is similar to that of less invasive treatments.”

The commentators continue: “Adding the risk of motor deficit of the thenar muscle and limited generalisability (only 60 of 370 screened participants were enrolled), further studies to assess the clinical feasibility of botulinum toxin A injection for base-of-thumb osteoarthritis are needed.”

medwireNews is an independent medical news service provided by Springer Healthcare Ltd. © 2022 Springer Healthcare Ltd, part of the Springer Nature Group

Lancet Rheumatol 2022; doi: 10.1016/S2665-9913(22)00129-1
Lancet Rheumatol 2022; doi: 10.1016/ S2665-9913(22)00155-2

Image Credits: © Astrid Gast / iStock

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Lucy Piper

medwireNews Bureau Chief