Abstract
Stimulation of the vagus nerve, a parasympathetic nerve that controls the neuro-digestive, vascular, and immune systems, induces pain relief, particularly in clinical conditions such as headache and rheumatoid arthritis. Transmission through vagal afferents towards the nucleus of the solitary tract (NST), the central relay nucleus of the vagus nerve, has been proposed as the main physiological mechanism that reduces pain intensity after vagal stimulation. Chronic pain symptoms of fibromyalgia patients might benefit from stimulation of the vagus nerve via normalization of altered autonomic and immune systems causing their respective symptoms. However, multi-session non-invasive vagal stimulation effects on fibromyalgia have not been evaluated in randomized clinical trials. We propose a parallel group, sham-controlled, randomized study to modulate the sympathetic–vagal balance and pain intensity in fibromyalgia patients by application of non-invasive transcutaneous vagus nerve stimulation (tVNS) over the vagal auricular and cervical branches. We will recruit 136 fibromyalgia patients with chronic moderate to high pain intensity. The primary outcome measure will be pain intensity, and secondary measures will be fatigue, health-related quality of life, sleep disorders, and depression. Heart rate variability and pro-inflammatory cytokine levels will be obtained as secondary physiological measures. We hypothesize that multiple tVNS sessions (five per week, for 4 weeks) will reduce pain intensity and improve quality of life as a result of normalization of the vagal control of nociception and immune–autonomic functions. Since both vagal branches project to the NST, we do not predict significantly different results between the two stimulation protocols.
Highlights
This study aims to explore the effects of multiple transcutaneous vagus nerve stimulation (tVNS) sessions on fibromyalgia This study aims to explore the effects of multiple tVNS sessions on fibromyalgia symptoms
Encouraging results have been reported for invasive vagal stimulation procedures in fibromyalgia treatment [31], but controlled clinical trials using non-invasive vagal stimulation are missing with respect to the effectiveness and safety of this neuromodulation option
We have described a non-invasive vagal nerve stimulation protocol aimed to ameliorate chronic pain and improve quality of life in fibromyalgia patients
Summary
In addition to chronic and generalized pain, the syndrome includes extreme fatigue, insomnia and other sleep disorders, affective and emotional disorders, such as depression and anxiety, cognitive impairment, paresthesia, allergy symptoms, joint stiffness, tendinopathy, neuropathic and rheumatologic symptoms, chemical and skin hypersensitivity, irritable bowel syndrome, and other symptoms whose common etiopathogenesis is unknown [1,2,3]. Because of the unknown biological mechanisms of fibromyalgia, current pharmacological therapies are aimed at alleviating its symptoms, and the efficacy of available treatments is limited [4]. Generalized pain and extreme fatigue are usually refractory to any therapeutic attempt [4,5]
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