Transcranial magnetic stimulation therapy (TMS) is a TGA-approved treatment for depression. Its role in the management of other non-psychiatric conditions is only just revealing itself.
As a cortical neuromodulation technique, it normalises the connectivity of damaged cortical networks through top-down processing. Research shows potential benefit of TMS in multiple sclerosis, tinnitus, traumatic brain injury, stroke-related disability, Alzheimer’s disease, Parkinson’s disease, autism, amyotrophic lateral sclerosis, obsessive compulsive disorder and post traumatic stress disorder. Neuropathic pain is one area leading the charge of its clinical application.
The modern use of neuromodulation as a pain treatment came from Melzack and Wall’s gate theory of pain in 1965. In 1967, Wall, Sweet and Avery created the first implantable stimulator and Shealy and Mortimer designed the implantable electrode for dorsal column stimulation. Tsubokawa (1991) demonstrated that stimulating the motor cortex could be of benefit and Migita (1995) reported the first case of extracranial magnetic motor cortex stimulation successfully treating a patient with centrally mediated deafferentation pain.
Jean-Pascal Lefaucheur led the way in subsequent research of TMS’s application to pain, concluding in 2020 that “high frequency stimulation of the motor cortex has level A evidence for analgesic efficacy in neuropathic pain”. Benefit was reported in other pain conditions ( migraine, complex regional pain syndrome, fibromyalgia, phantom limb and bladder pain syndromes).
TMS’s mechanism of action in pain is complex, involving downward modulation of cortical excitability at the stimulation site and transynaptically at more distant areas. These areas include the affective, cognitive and emotional aspects of pain processing via the cingulate, prefrontal and orbitofrontal cortices.
In this network, known as the pain matrix, TMS enhances the release of endogenous opioids and inhibitory neurotransmitters (e.g. GABA). In localised neuropathic pain the contralateral motor cortex is the primary stimulation site. In more widespread nociplastic type pain the left motor cortex and dorsolateral pre-frontal cortex are often targeted. Lefaucher and Nguyen (2019) reported at least 10 sessions were needed before any analgesic benefit was likely to be seen.
Advantages
TMS could be a viable and safer alternative to opioids and may help to reduce opioid use in patients with chronic pain. TMS has few side effects – scalp tenderness and headache being the most common but typically resolving by the third treatment. A theoretical risk of seizures is lower than the use of an opioid analgesic. As a non-invasive non-medication treatment it has not revealed any adverse interaction with other medical therapies. With sessions lasing around 20 minutes, it is convenient and time effective. Patients could be back at work before their 30-minute lunch break ends!
Cost is now less of a barrier. The 2021 federal budget announced funding of TMS for patients with medication-resistant depression. The Medicare code is set to begin on November 1. Similarly, Department of Veteran Affairs supports TMS treatment of depression. Worker’s compensation and motor vehicle insurance providers variably support its use.
TMS for pain does have limitations. How to best sustain the analgesic efficacy is not yet clear and it is likely to have wide variation across the population. However, maintenance therapy (possibly monthly sessions for six months) may be the best technique in achieving this objective.
Pain treatment necessitates MRI-guided brain mapping to ensure safe and precise cortical targeting. The surface anatomy approach used in the treatment of depression does not afford the accuracy required to target pain.
TMS uses magnetic energy, so the contraindications are similar to MRI brain imaging – metalware above the cervical area. Care needs to be taken when there is a history of epilepsy. As an off-label treatment, TMS’s role in pain management requires full disclosure and informed consent.
TMS is an emerging treatment in the pain management arsenal. A neuromodulatory technique that offers a non-opioid option. Refreshingly, it could serve the goal of facilitating the patient’s own self efficacy, the decisive goal of chronic pain management.
Key messages
- TMS is a novel, effective treatment for neuropathic and nociplastic pain conditions
- It is a non-invasive and safe alternative when other conventional pain treatments have failed
- Patients with comorbid chronic pain and mental illness may particularly benefit.
– References available on request
Author competing interests – the author is director of a company providing TMS services