Botulinum toxin eased painful foot dystonia in Parkinson's — in a 33-patient trial

Painful cramping of the foot — toes curling, the sole twisting inward — is one of the more disabling and least-studied symptoms of Parkinson's disease. It often strikes during "OFF" periods, when a dose of levodopa is wearing thin, and it frequently resists the usual adjustments to medication [s1]. A small randomised trial now reports that injecting onabotulinumtoxinA (BTXA), the same botulinum preparation marketed for wrinkles and for other dystonias, into specific foot muscles reduced that pain without blunting movement [s1]. The result is encouraging and, importantly, placebo-controlled — but it rests on just 33 patients at a single centre.

What the trial did

The study was a single-centre, randomised, double-blind, placebo-controlled trial conducted by investigators at the University of Calgary, registered as NCT04277247 [s1][s2]. Adults with unilateral Parkinson's disease and painful foot dystonia that had not responded to medication optimisation were randomised 1:1 to receive either BTXA at a dose of 100 units or a matching placebo, delivered through a guided injection protocol targeting three muscles: the tibialis posterior, the extensor hallucis longus, and the flexor digitorum brevis [s1]. Outcomes were assessed at 6 and 12 weeks, after which all participants could enter a 12-week open-label extension [s1].

The primary outcome was the change from baseline in dystonia-related pain, measured with Item 5 of the King's Parkinson's Disease Pain Scale (KPPS), a validated instrument for the varied pains of Parkinson's [s1]. Secondary measures included responder rates — defined as at least a 30% reduction in pain — along with pain severity and frequency sub-scores, a visual analogue scale, motor ratings on the Movement Disorder Society's Unified Parkinson's Disease Rating Scale, quality of life, and safety [s1].

What it found

Thirty-three participants were randomised, 16 to BTXA and 17 to placebo [s1]. On the primary measure, BTXA produced a significantly greater reduction in dystonia-related pain than placebo at 6 weeks, with a mean difference of −3.60 points on KPPS Item 5, and the benefit was sustained at 12 weeks (p < 0.001) [s1]. The between-group effect size was large: Hedges' g of −1.33 (95% confidence interval −2.13 to −0.53) [s1].

The responder analysis pointed the same way. Three-quarters of the BTXA group — 75.0% — met the threshold of at least a 30% pain reduction at both 6 and 12 weeks, against 11.8% and 5.6% of the placebo group at those time points, respectively (p < 0.001) [s1]. Pain severity and frequency sub-scores and the broader KPPS Domain 3 total also improved at both time points [s1]. The visual analogue scale fell at 6 weeks, but by 12 weeks the gap between groups was no longer significant — a reminder that different pain instruments can disagree even within one trial [s1]. Crucially, there were no differences between groups in motor outcomes, quality of life, or adverse events, which were mild [s1]. That matters because botulinum toxin weakens the muscle it is injected into, and the worry with foot injections is always that relieving a cramp could come at the cost of walking.

How to read it

The strengths here are real: this was a properly randomised, double-blind, placebo-controlled design in a symptom where evidence has been thin, and it used a disease-specific pain scale rather than a generic one [s1]. The large effect size and the convergence of several pain measures lend the finding some weight.

The limits are equally real, and the authors do not hide them. Thirty-three participants is a very small sample, and small trials tend to overstate the size of a true effect — the wide confidence interval around the effect size reflects exactly that uncertainty [s1]. It was conducted at a single centre with a specialised, image- or anatomy-guided injection technique, so the results may not transfer to clinics that inject differently [s1]. The registry lists the study as a phase 2/3 trial with a planned enrolment of 40, short of which it stopped [s2]. And the follow-up was short: 12 weeks, with the open-label extension unable to answer whether repeated injections keep working or how often they are needed [s1]. The divergence between the KPPS and the visual analogue scale at 12 weeks is a further note of caution [s1].

What to watch

The open questions are the practical ones: whether a larger, multi-centre trial reproduces the effect, how durable the relief is across repeated dosing cycles, and which patients — by pattern of dystonia or injection site — benefit most [s1][s2]. Botulinum toxin is already used off-label for limb dystonias, so this trial formalises a common practice rather than introducing a new one. This article describes research and is not medical advice; decisions about botulinum injections in Parkinson's disease belong with a treating neurologist.

Sources

• OnabotulinumtoxinA for Painful Foot Dystonia in Parkinson Disease: A Randomized, Double-Blind, Placebo-Controlled Trial — Neurology: Clinical Practice, 17 September 2026
• Botulinum Toxin Type A for Foot Dystonia-associated Pain in Parkinson's Disease (NCT04277247) — ClinicalTrials.gov