Is rTMS a therapeutic option in chronic pain syndrome? Insights from the treatment of fibromyalgia

Transcranial magnetic stimulation in exploring neurophysiology of cortical circuits and potential clinical implications

Transcranial magnetic stimulation (TMS) is a non-invasive, painless technique to stimulate the human brain. Although it has been used in clinical research both as an investigative tool and treatment modality for the past three decades, its use has been restricted to tertiary health centres or higher-end academic research institutions. The aim of this review is to popularise the concepts of this effective non-invasive brain stimulation technique, further facilitating its use both in research and clinical practice among clinical physiologists. In the first part of this article, a brief physiologic overview of TMS will be provided with basic as well as the basic technical details. This is followed by a discussion of TMS parameters that can be studied using single and paired pulses of TMS which could be used to investigate the altered excitability of cortical circuits. Finally, how rTMS and patterned TMS could be used to induce plasticity which, in turn, could be potentially used as therapeutic interventions in various neurological and psychiatric disorders will be illustrated. In each section of this article, diagnostic as well as therapeutic utilities of TMS in Neurology and Psychiatric disorders will be discussed. These discussions could not only facilitate the understanding of pathophysiology of mood and movement disorders but also to manage various neurological and psychiatric disorders with novel therapeutic options. In the end, few future directions, limitations of this technique and comparison with other techniques will be provided. I hopefully, this review would elicit some interest in physiologists to take up this exciting area of brain stimulation as a research subject and work further on understanding the functions of brain and use it effectively in the management of various brain-related disorders.

Cortical neurostimulation for neuropathic pain: state of the art and perspectives

The treatment of neuropathic pain by neuromodulation is an objective for more than 40 years in modern clinical practice. With respect to spinal cord and deep brain structures, the cerebral cortex is the most recently evaluated target of invasive neuromodulation therapy for pain. In the early 90s, the first successes of invasive epidural motor cortex stimulation (EMCS) were published. A few years later was developed repetitive transcranial magnetic stimulation (rTMS), a noninvasive stimulation technique. Then, electrical transcranial stimulation returned valid and is currently in full development, with transcranial direct current stimulation (tDCS). Regarding transcranial approaches, the main studied and validated target was still the motor cortex, but other cortical targets are under investigation. The mechanisms of action of these techniques share similarities, especially between EMCS and rTMS, but they also have differences that could justify specific indications and applications. It is therefore important to know the principles and to assess the merit of these techniques on the basis of a rigorous assessment of the results, to avoid fad. Various types of chronic neuropathic pain syndromes can be significantly relieved by EMCS or repeated daily sessions of high-frequency (5-20 Hz) rTMS or anodal tDCS over weeks, at least when pain is lateralized and stimulation is applied to the motor cortex contralateral to pain side. However, cortical stimulation therapy remains to be optimized, especially by improving EMCS electrode design, rTMS targeting, or tDCS montage, to reduce the rate of nonresponders, who do not experience clinically relevant effects of these techniques.

Pain

Invasive stimulation of the motor (precentral) cortex using surgically implanted epidural electrodes is indicated for the treatment of neuropathic pain that is refractory to medical treatment. Controlled trials have demonstrated the efficacy of epidural motor cortex stimulation (MCS), but MCS outcome remains variable and validated criteria for selecting good candidates for implantation are lacking. Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive approach that could be used as a preoperative tool to predict MCS outcome and also could serve as a therapeutic procedure in itself to treat pain disorders. This requires repeated rTMS sessions and a maintenance protocol. Other studies have also demonstrated the efficacy of transcranial direct current stimulation (tDCS) in relieving chronic pain syndromes. The most studied target is the precentral cortex, but other targets, such as the prefrontal and parietal cortices, could be of interest. The analgesic effects of cortical stimulation relate to the activation of various circuits modulating neural activities in remote structures, such as the thalamus, limbic cortex, insula, or descending inhibitory controls. In addition to the treatment of refractory neuropathic pain by epidural MCS, new developments of this type of strategy are ongoing, for other types of pain syndrome and stimulation techniques.

Prevalence, clinical features and potential therapies for fibromyalgia in primary headaches

Fibromyalgia (FM) syndrome is predominantly related to generation and persistence of central sensitization, which is an aggravating factor for chronic headaches. This review aims to examine the last 11 years of studies on FM and primary headache comorbidity, focusing on prevalence, clinical features and treatments. Chronic forms of migraine and tension-type headache show a high frequency of FM comorbidity. The symptoms characterizing headache patients presenting with FM comorbidity are high headache frequency, poor sleep quality, pericranial tenderness, anxiety and reduction of physical performances. The effects of headache-preventive drugs on factors favoring FM comorbidity were poorly evaluated. Nonpharmacological approaches such as transcranial magnetic stimulation may be an option for treatment of chronic migraine associated with FM.

Efficacy of transcranial direct current stimulation and repetitive transcranial magnetic stimulation for treating fibromyalgia syndrome: a systematic review

OBJECTIVE

 To systematically review the literature to date applying repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS) for patients with fibromyalgia syndrome (FMS).

METHOD

 Electronic bibliography databases screened included PubMed, Ovid MEDLINE, PsychINFO, CINAHL, and Cochrane Library. The keyword "fibromyalgia" was combined with ("transcranial" and "stimulation") or "TMS" or "tDCS" or "transcranial magnetic stimulation" or "transcranial direct current stimulation".

RESULTS

 Nine of 23 studies were included; brain stimulation sites comprised either the primary motor cortex (M1) or the dorsolateral prefrontal cortex (DLPFC). Five studies used rTMS (high-frequency-M1: 2, low-frequency-DLPFC: 2, high-frequency-DLPFC: 1), while 4 applied tDCS (anodal-M1: 1, anodal-M1/DLPFC: 3). Eight were double-blinded, randomized controlled trials. Most (80%) rTMS studies that measured pain reported significant decreases, while all (100%) tDCS studies with pain measures reported significant decreases. Greater longevity of significant pain reductions was observed for excitatory M1 rTMS/tDCS.

CONCLUSION

 Studies involving excitatory rTMS/tDCS at M1 showed analogous pain reductions as well as considerably fewer side effects compared to FDA apaproved FMS pharmaceuticals. The most commonly reported side effects were mild, including transient headaches and scalp discomforts at the stimulation site. Yearly use of rTMS/tDCS regimens appears costly ($11,740 to 14,507/year); however, analyses to apapropriately weigh these costs against clinical and quality of life benefits for patients with FMS are lacking. Consequently, rTMS/tDCS should be considered when treating patients with FMS, particularly those who are unable to find adequate symptom relief with other therapies. Further work into optimal stimulation parameters and standardized outcome measures is needed to clarify associated efficacy and effectiveness.

Fibromyalgia: a primer for the anesthesia community

PURPOSE OF REVIEW

The present review is intended to give an overview of fibromyalgia for the anesthesiologist. While the basics of the treatment of fibromyalgia are included, the intent is to provide context to discuss the potential implications in perioperative management.

RECENT FINDINGS

Research continues to demonstrate that fibromyalgia patients have neurophysiologic abnormalities that alter sensory perception, including lower levels of central neurotransmitters associated with the inhibition of pain and higher levels those that facilitate pain. While comorbid mood disorders are more common in fibromyalgia patients, studies have shown that fibromyalgia symptoms are not explained by depression alone. In the last year, the American College of Rheumatology established a new self-report questionnaire for the diagnosis of fibromyalgia in lieu of the previously required tender point examination plus self-report questionnaire. This questionnaire allows for the study of the severity of sensitivity and symptomatology on a continuum, which is termed 'fibromyalgianess'. Some new concepts in the treatment have been proposed, including sodium oxybate, transcranial magnetic stimulation, and web-based cognitive behavioral therapy.

SUMMARY

The impact of fibromyalgia on anesthesia care is not known. Years of quality research have clearly demonstrated multiple pathophysiologic changes that could impact anesthesia care and future study is needed.