Transcranial Magnetic Stimulation for Chronic Pain

Introduction

What is transcranial magnetic stimulation (TMS)?

TMS is a non-invasive brain stimulation technique that can be effective for treating psychiatric and neurological disorders.¹

What is chronic pain?

Chronic pain is defined as ongoing pain that persists for longer than 3 months, or exceeds the typical healing process, for example, body aches that accompany flu may persist even after the virus has cleared from the body.²

TMS for chronic pain management

When nerves detect pain-causing stimuli, signals are sent to the brain causing us to feel pain. Research suggests that chronic pain may decrease when the superficial layer of the brain, known as the cerebral cortex, is stimulated. TMS follows this mechanism by sending signals from the brain to interfere with the abnormal signals that are causing the pain.³

Understanding chronic pain

Types of pain

Pain can be organised into the following categories, often depending on where it originates in the body:

• Neuropathic – peripheral (eg. diabetic neuropathy) and central
• Nociceptive – damage to tissues (e.g. burns)
• Musculoskeletal – bones, muscles
• Inflammatory – autoimmune disorders (e.g. rheumatoid arthritis), infection
• Psychogenic – psychological or behavioural factors (e.g. depression, anxiety)
• Mechanical – lumbago, soft tissue pain⁴

Mechanisms and causes of chronic pain

The brain functions to decipher signals and work out if a response is needed; this usually manifests in the feeling of pain. In chronic pain the brain becomes overly sensitive to these signals and may struggle to accurately interpret them, resulting in the constant firing of pain signals even when no harm or damage is actually present.²

Primary disease is the key cause of chronic pain. For example, you may contract a viral illness, such as glandular fever and continue to experience body aches long after the infection has resolved. The end result is an example of chronic pain known as ‘fibromyalgia’. Other instances include long-lasting headaches after a stroke and osteoarthritis following an injury.

Where possible, chronic pain is about treating the underlying cause. Without an obvious reason for the pain, doctors cannot target the primary issue which prevents the resulting pain from being resolved. Unknown causes may make it difficult for you to come to terms with your symptoms. This could result in subsequent psychological conditions which are likely to worsen your physical pain.⁴ 

Impact on quality of life and daily functioning

Poorly managed chronic pain can have a debilitating impact on a person’s life. You may struggle to cope with simple activities like washing and dressing. Also, there is an increased risk of developing psychological conditions secondary to the pain. Pain-related expenses constitute a significant proportion of NHS funding, so if we can treat acute pain before it becomes chronic, patients can better recover from initial diseases; this allows them to live as good a quality of life as possible whilst alleviating pressure on limited NHS resources too.⁵

Mechanism of TMS

How does TMS change neural activity?

TMS uses electromagnetic induction to deliver magnetic pulses into the brain, causing a change in the electrical activity. This typically includes a decrease in the firing of pain signals from nerve endings, thus alleviating the pain that a person is feeling.⁶

How is TMS carried out?

During the procedure, a plastic-coated coil is held against the head, allowing the magnetic pulses to be sent into the brain through the skull. In order to determine where the coil should be positioned, a magnetic resonance imaging (MRI) scan is used to pinpoint the site of maximum pain. Then, magnetic pulses are fired in succession over 10 or 20 seconds with a 30-second interval between each round.³ 

Effectiveness of TMS for chronic pain

A systematic review published in 2020 found that TMS was effective for treating neuropathic pain, fibromyalgia and migraine, owing to reduced pain scores from patients following this treatment.⁷

Another study also noted that TMS provided effective, long-term relief in patients with chronic lower back pain.⁸

Furthermore, TMS reduced pain scores in some patients with chronic facial pain, including cluster headaches, that had failed to resolve with other treatments.⁹

TMS compared to conventional treatments

TMS does not require any sedation and recovery time is quick. For instance, carrying out a hip replacement for hip pain is a lengthy operation that requires general anaesthesia, whereas TMS is non-invasive and more efficient, making it a better treatment option.

Also, TMS is preferable for chronic pain management rather than treatment with opioids due to the risk of dependency that comes with long-term opioid use. Moreover, TMS does not cause common side effects that are often associated with pharmacotherapy, for example nausea, drowsiness or rash.¹⁰ 

Safety and side effects

Although research has demonstrated the effectiveness of TMS for chronic pain management, there are also some risks involved.

Common side effects of TMS therapy

During the procedure, the coil can make a loud clicking noise which can be uncomfortable, particularly if you have hearing problems or are sensitive to loud sounds. Earplugs can be worn to eliminate this issue.

Headache and fatigue are common complaints following TMS but they tend to be mild and do not require intervention. You may feel slightly dizzy after the procedure but this generally resolves quickly.

Finally, it is common for pain to temporarily increase before you feel a noticeable improvement in your symptoms.³

Limitations of TMS

• TMS may not work for everyone with chronic pain – effectiveness depends on the underlying cause and individual factors.
• TMS needs to be delivered over several sessions to achieve maximum benefit – this requires you to be committed to your treatment.
• TMS often needs to be combined with other treatment methods (e.g. pharmacotherapy, lifestyle changes) to provide the best symptom improvement – these other treatment methods may have undesirable side effects.
• Although the short-term use of TMS for chronic pain management is promising, there is lack of evidence as to whether TMS is safe to use in the long term too.¹⁰ 

Safety considerations for specific patient populations

There is a risk of epileptic seizure following the procedure, albeit very small and is outweighed by the benefit of TMS. However, for the patient population who currently  have seizures, or have previously experienced them, alternative treatments to TMS are generally advised. The healthcare professional carrying out TMS is trained to deal with seizures in the unlikely event that they happen.³ 

Future directions and challenges

Variations in treatment protocols

The current protocols for TMS are highly variable in terms of the duration and frequency of the treatment,¹¹ making it difficult for clinicians to determine a suitable treatment plan for their patients. Further research is needed so a stimulation protocol that provides optimum relief for chronic pain management can be developed.¹² 

Ongoing research into TMS

Some studies into TMS for chronic pain actually show a decrease in the pain-relieving effect of the treatment if carried out in the long term. Research is ongoing to see if it is indeed safe and effective to perform TMS repeatedly to allow you to achieve and maintain a continuous reduction in your pain symptoms.

Optimising treatment outcomes

One of the major drawbacks of TMS is that it might not prove effective for everyone with chronic pain. This opens up a gap in research to find out if more specific treatment protocols that account for individual differences in each patient can be created. For instance, there are slight variations in the brain anatomy of each person and this will affect exactly where the coil must be placed on the head.⁶

Development of TMS technology

TMS is typically carried out in a hospital but for those with chronic pain, getting to such a facility may be difficult. There is currently a portable TMS machine that has been FDA approved for treatment of migraine pain, so this raises questions as to whether portable machines for other types of chronic pain can be developed too.¹³

Regulatory and ethical considerations in TMS

Ethical and regulatory issues are a major factor to consider in medicine, for example when designing clinicals trials or administering treatments to patients.

Firstly, you should give valid and informed consent before undergoing TMS. This means that your decision to participate must be voluntary and you must be fully aware of the procedure and the risks involved.

In order to expand the use of TMS for chronic pain, research must continue to demonstrate that the benefit of the procedure outweighs any risk; this is particularly important when considering if TMS can be used long term.¹⁴

As previously mentioned, TMS is not always effective for everyone. Therefore, when deciding who is eligible for this treatment, patients should be comprehensively screened on an individual basis to identify those who are likely to best respond to it. This will ensure no one is unnecessarily subjected to the procedure and its potential risks.¹⁵

Summary

• TMS can be used to treat chronic pain; it does this by sending magnetic pulses into the brain, resulting in altered electrical activity and a decrease in pain signals.
• TMS is generally a safe procedure, owing to its non-invasive nature and quick recovery time.
• The limitations include side effects (.e.g. fatigue, dizziness), the small likelihood of a seizure occurring and the uncertainty as to whether TMS can be used in the long term.
• Future research should aim to improve treatment protocols, develop better TMS technology and confirm whether patients can undergo TMS on a long-term basis.