Vagus nerve stimulation in musculoskeletal diseases.

The vagus nerve is the main nerve of the parasympathetic autonomic nervous system. Beyond its vegetative functions, the vagus nerve possesses anti-inflammatory and analgesic properties. Initially developed in the treatment of refractory epilepsy, vagus nerve stimulation (VNS) is currently being evaluated in several musculoskeletal diseases. VNS can be invasive by placing an electrode around the cervical vagus nerve and connected to a generator implanted subcutaneously or non-invasive stimulating the cervical vagus nerve branch percutaneously (auricular or cervical). In rheumatoid arthritis (RA) patients, VNS has been shown to dampen the inflammatory response of circulatory peripheral cells. Several open-labeled small pilot studies have demonstrated that VNS, either invasive or transcutaneous, is associated with a significant decrease of RA disease activity. As well, other studies have shown that VNS could limit fatigue in Sjogren's syndrome and systemic lupus, or decrease pain in fibromyalgia as well as in erosive hand osteoarthritis. However, some questions remain, such as the settings of stimulation, the duration of treatment, or the optimal stimulation route. Finally, randomized controlled trials versus sham stimulation with large samples of patients are mandatory to definitively conclude about the efficacy of VNS.