# Efficacy of TENS in Cervical Pain Syndromes: An Umbrella Review of Systematic Reviews
## 4 Discussion  
Neck pain has a multifactorial etiology. The precise identification of the structure causing the pain is very difficult, not only because the various structures are innervated by several segments, but also because facilitation-convergence and sensitization mechanisms favor the phenomenon of referred pain [41]. Psycho-social factors are frequently found in subjects with persistent pain and judged responsible for a reduction in the pain threshold,which is why, given the current conception of cervical pain, it is recommended to consider the bio-psycho-social unity of the subject with neck pain, paying attention not only to the clinical aspects (severity and duration), but also to the personal, cultural, and social (environmental) dimensions that characterize the patient, as well as to the impact of the problem on daily life activities [42; 43]. The presence of numerous visceral and nervous structures requires careful collection of information in order to exclude the presence of \"red flags\", or signs and symptoms attributable to the presence of other pathologies, which can cause symptoms similar to that of neck pain [44; 45]. In the presence of chronic musculoskeletal pain, both alterations in the processing of information by the central nervous system and an increased reactivity of central neurons were found, all of which predisposes to central pain sensitization; in this condition each new peripheral lesion can become a new source of nociceptive input that maintains or aggravates the painful condition [46; 47]. The pathophysiological mechanisms underlying most conditions associated with chronic pain are still unclear. In 90% of cases, however, the disorder is non-specific; only in 0.4% is it related to serious pathologies and in 3% to fractures derived from trauma. In case of referred pain, distant from the cervical region, the presence of irradiated symptoms must be assumed [47]. Muscles are also able to cause the onset of pain in areas distant from the cervical region, due to the presence of trigger points. The trigger point is a relatively small, contracted nodular type tissue modification, which is located within a taut band of a muscle fiber, it is quite sensitive to touch and can generate pain locally and in distant areas called target areas. Trigger points can be both active and latent; primary if they concern the muscle directly subjected to overload, or secondary if activated in a distant muscle. The muscles that most frequently develop trigger points are the trapezius, the sternocleido-mastoid, the sub-occipital muscles, the spleni, and the levator scapula [1]. A further cause of neck pain can be facet joint syndrome, which can affect the cervical or lumbar spine. The articular facets are vertebral bone structures that have the function of connecting the vertebrae to each other allowing the movements of the spine [10; 11]. When joint damage occurs as a result of trauma or arthritic phenomena, pain occurs. The mechanism of onset is due to the cartilage damage that causes a \"rubbing\" between the two bone surfaces, with consequent inflammation; this in turn can lead to the formation of osteophytes. The same physiological deterioration of cartilage, which occurs with advancing age, can irritate the nerves that innervate the facet joints, thus contributing to the onset of pain [10; 11; 12]. The 11 systematic reviews included in the umbrella review show that TENS is able to reduce pain but does not appear to be more effective than other routinely used therapies. Some studies shown that TENS is effective in managing neck pain, but only in the short term. TENS showed no lasting effects over time. One review [25] provides inconclusive evidence of the benefit of TENS in patients suffering from chronic neck pain due to the low quality of the studies and the heterogeneity of the same. The studies show that no type of TENS application prevails over the others, moreover, when administered together with other therapies, it does not bring further benefits.