Botulinum Toxin for Thoracic Outlet Syndrome: What the Evidence Shows and Who May Benefit
Botulinum Toxin (Botox) Injections for Thoracic Outlet Syndrome
Rationale, evidence, muscle targets, and the Pain Spa approach
Key message
Botulinum toxin injections are not a proven cure for thoracic outlet syndrome, but they may provide short-lived symptom relief in carefully selected patients with neurogenic thoracic outlet syndrome, and can sometimes help clarify whether surgery is likely to help.
Contents
- What is thoracic outlet syndrome?
- Why TOS is often missed or misdiagnosed
- Why muscle overactivity matters in neurogenic TOS
- What is botulinum toxin and how might it help?
- What does the evidence actually show?
- Which muscles are targeted and why?
- Why ultrasound guidance is essential
- Who may benefit, and who is unlikely to benefit?
- What to expect from the procedure
- How Botox fits into a broader treatment plan
- The Pain Spa approach
- Summary
- FAQs
What is thoracic outlet syndrome?
Thoracic outlet syndrome (TOS) refers to symptoms caused by irritation or compression of nerves or blood vessels as they pass from the neck into the arm through the thoracic outlet.
There are three key anatomical regions where compression can occur: the interscalene triangle (between the anterior and middle scalene muscles), the costoclavicular space (between the clavicle and first rib), and the retro-pectoralis minor (subcoracoid) space (near the coracoid process).
TOS is commonly classified as neurogenic TOS (nerve-related), venous TOS, or arterial TOS. This article focuses on neurogenic thoracic outlet syndrome (nTOS), the most common type, where symptoms arise predominantly from brachial plexus irritation.
Why TOS is often missed or misdiagnosed
TOS can be difficult to diagnose because symptoms overlap with other conditions such as cervical radiculopathy (nerve root irritation in the neck), shoulder pathology, peripheral nerve entrapments, and myofascial pain.
In addition, many cases are dynamic: symptoms may fluctuate with posture, arm position, activity, and muscle tension. Imaging tests are useful for excluding other diagnoses, but normal scans do not rule out neurogenic TOS.
Why muscle overactivity matters in neurogenic TOS
In many patients with neurogenic TOS, symptoms are driven by functional narrowing of the thoracic outlet due to muscle overactivity, hypertrophy, or chronic guarding, rather than a single fixed structural blockage.
Tight or overactive muscles can reduce the space available for the brachial plexus, increase mechanical irritation during arm movement, and perpetuate a cycle of pain, protective spasm, and sensitisation.
What is botulinum toxin and how might it help?
Botulinum toxin (often known as Botox) temporarily reduces muscle overactivity by blocking acetylcholine release at the neuromuscular junction. In thoracic outlet syndrome, the goal is not paralysis, but controlled reduction in excessive tone in carefully selected muscles.
By relaxing targeted muscles, botulinum toxin aims to widen the relevant anatomical space, reduce brachial plexus irritation, and help break the cycle of pain and guarding so that rehabilitation can be more effective.
Important
Botulinum toxin injections are not a cure for thoracic outlet syndrome. Evidence suggests that a proportion of carefully selected patients experience meaningful short-term relief, while others do not notice enough benefit to repeat the procedure.
What does the evidence actually show?
Systematic reviews of botulinum toxin injections for neurogenic TOS report short-term symptom improvement in a subset of patients, but results are variable and overall evidence quality is limited. Randomised controlled data are scarce, and not all studies show a clear clinically important benefit.
Where benefit occurs, it is typically temporary, often lasting weeks to a few months. Importantly, some studies suggest that outcomes may be better when injections are performed with imaging guidance (such as ultrasound) and when muscle selection includes more than one potential compression site, for example including pectoralis minor in selected patients.
In specialist centres, response to botulinum toxin is sometimes used as a functional test to help clarify whether symptoms are likely to improve with surgical decompression, although this approach is not definitive and must be interpreted in the context of the overall clinical assessment.
Which muscles are targeted and why?
Choosing the right muscles is essential. The thoracic outlet includes multiple potential compression zones, so treatment needs to be individualised rather than “one size fits all.” Below are the main muscles that may be considered in neurogenic TOS and the rationale for targeting them.
Anterior scalene
The anterior scalene forms the front boundary of the interscalene triangle. Overactivity or hypertrophy can narrow this space and irritate the brachial plexus.
Botulinum toxin here aims to reduce excessive tone, decrease dynamic crowding in the interscalene region, and reduce nerve irritation during arm movement.
Middle scalene
The middle scalene forms the other boundary of the interscalene triangle. When overactive, it can further crowd the brachial plexus and amplify symptoms.
Targeting the middle scalene may complement anterior scalene relaxation and improve space for the brachial plexus in patients whose symptoms suggest interscalene compression.
Pectoralis minor
In some patients, compression is more prominent beneath the coracoid process in the retro-pectoralis minor (subcoracoid) space. Tightness or shortening of pectoralis minor can pull the shoulder girdle forward and compress the neurovascular bundle.
Botulinum toxin to pectoralis minor may be helpful when symptoms and examination suggest subcoracoid compression, such as anterior chest or axillary discomfort and posture-related symptom provocation.
Subclavius (selected cases)
The subclavius lies under the clavicle and can contribute to narrowing of the costoclavicular space. Although less commonly the main driver, subclavius hypertrophy can be a dominant factor in selected occupational or sporting presentations.
Specialist ultrasound assessment can sometimes identify subclavius hypertrophy and guide targeted injection where appropriate.
Why ultrasound guidance is essential
High-resolution ultrasound allows real-time visualisation of key structures, including the target muscles, brachial plexus elements, subclavian vessels, pleura, and lung apex. This supports both accuracy and safety.
Ultrasound guidance helps ensure that the botulinum toxin is delivered to the intended muscle while avoiding critical structures. It also allows dosing to be focused within the most relevant parts of the muscle rather than relying on external landmarks alone.
Why we always use ultrasound guidance at Pain Spa
All Botox injections for thoracic outlet syndrome at Pain Spa are performed with ultrasound guidance to maximise precision and safety, and to support an individualised muscle-selection approach based on each patient’s anatomy and symptom pattern.
Who may benefit, and who is unlikely to benefit?
Who may benefit
- Predominantly neurogenic symptoms (pain, tingling, heaviness, fatigue, weakness).
- Clinical features suggesting dynamic, muscle-related compression.
- Symptoms persisting despite structured conservative management.
- No red flags requiring urgent vascular or surgical assessment.
Who is less likely to benefit
- Symptoms primarily due to cervical nerve root compression or another clear diagnosis.
- Predominant vascular TOS features without neurogenic drivers.
- Widespread pain without evidence of focal dynamic compression.
- Expectations of permanent cure from a temporary neuromodulatory injection.
What to expect from the procedure
The injection is usually performed as a day-case procedure. The aim is targeted, ultrasound-guided delivery into selected muscles contributing to thoracic outlet narrowing.
If benefit occurs, it often begins within days to a few weeks and is typically temporary, lasting weeks to a few months. Many patients use this window to engage more effectively with rehabilitation.
Possible side effects
- Temporary soreness or bruising at the injection site.
- Temporary weakness in the targeted muscle group.
- Transient voice or swallowing changes can occur with scalene-region injections, depending on anatomy and spread (uncommon).
- Serious complications are rare, and ultrasound guidance helps reduce risk by visualising nearby blood vessels and pleura.
How Botox fits into a broader treatment plan
Botulinum toxin injections are usually considered as part of a broader strategy rather than a stand-alone solution. In most cases, they are combined with specialist physiotherapy, posture and movement retraining, and nerve rehabilitation techniques.
In selected patients, response to Botox can provide useful information about whether symptoms are primarily driven by muscle-related compression and whether a surgical opinion may be appropriate.
The Pain Spa approach
At Pain Spa, we focus on careful diagnosis, exclusion of mimicking conditions, and realistic expectation-setting. The goal is to offer the right intervention for the right patient at the right time, using high-quality ultrasound guidance to support precision and safety.
Where Botox is appropriate, we tailor muscle selection and technique to each patient’s anatomy and symptom pattern, and we integrate injections into a broader plan that prioritises rehabilitation and long-term function.
Call to action
If you have been told you have thoracic outlet syndrome, or suspect it may be contributing to your symptoms, you can contact Pain Spa to arrange a consultation and individual assessment to discuss whether ultrasound-guided Botox injections may be appropriate for you.
Summary
- Botulinum toxin injections are not a cure for thoracic outlet syndrome.
- Evidence suggests short-term symptom relief in some carefully selected patients with neurogenic TOS.
- Target muscle selection matters (scalenes and, in selected cases, pectoralis minor and subclavius).
- Ultrasound guidance improves precision and supports safety.
- Botox works best as part of a broader rehabilitation-led plan.
FAQs
How long does Botox last for thoracic outlet syndrome?
If it helps, the effect is usually temporary and often lasts weeks to a few months, although individual responses vary.
Does Botox prove I have thoracic outlet syndrome?
A positive response can support the idea that muscle-related compression is contributing, but it is not a definitive diagnostic test and must be interpreted alongside the full clinical assessment.
Can Botox help me avoid surgery?
Some patients obtain worthwhile short-term relief that helps them progress with rehabilitation. Others may use response to guide whether a surgical opinion is appropriate. It is not a guaranteed alternative to surgery.
Is ultrasound guidance important?
Yes. Ultrasound allows real-time visualisation of the target muscles and nearby nerves, blood vessels, and pleura, improving accuracy and supporting safety.
References (selected)
Woodworth TT, Le A, Miller C, et al. Botulinum toxin injections for the treatment of neurogenic thoracic outlet syndrome: a systematic review. Muscle & Nerve. 2024.
Kök M, Schropp L, van der Schaaf IC, et al. Systematic Review on Botulinum Toxin Injections as Diagnostic or Therapeutic Tool in Thoracic Outlet Syndrome. Ann Vasc Surg. 2023.
Gharaei H, Gholampoor N. Optimizing Pain Relief in Refractory Thoracic Outlet Syndrome: The Role of Ultrasound-Guided Injections. Pain Physician. 2025.
Cavallieri F, Galletti S, et al. Botulinum Toxin Treatment for Thoracic Outlet Syndrome Induced by Subclavius Muscle Hypertrophy. NeuroSci. 2021.