Lack of Evidence for Central Sensitization in Idiopathic, Non-Traumatic Neck Pain: A Systematic Review

Background: Chronic neck pain is a common problem with a poorly understood pathophysiology. Often nounderlying structural pathology can be found and radiological imaging findings are more related to age thanto a patient’s symptoms. Besides its common occurrence, chronic idiopathic neck pain is also very disablingwith almost 50% of all neck pain patients showing moderate disability at long-term follow-up. Centralsensitization (CS) is defined as “an amplification of neural signaling within the central nervous system that elicitspain hypersensitivity,” “increased responsiveness of nociceptive neurons in the central nervous system to theirnormal or subthreshold afferent input,” or “an augmentation of responsiveness of central neurons to inputfrom unimodal and polymodal receptors.” There is increasing evidence for involvement of CS in many chronicpain conditions. Within the area of chronic idiopathic neck pain, there is consistent evidence for the presenceand clinical importance of CS in patients with traumatic neck pain, or whiplash-associated disorders. However,the majority of chronic idiopathic neck pain patients are unrelated to a traumatic injury, and hence are termedchronic idiopathic non-traumatic neck pain. When comparing whiplash with idiopathic non-traumatic neckpain, indications for different underlying mechanisms are found.Objective: The goal of this article was to review the existing scientific literature on the role of CS inpatients with chronic idiopathic non-traumatic neck pain.Study Design: Systematic review.Setting: All selected studies were case control studies.Methods: A systematic search of existing, relevant literature was performed via the electronicdatabases Medline, Embase, Web of Science, Cinahl, PubMed, and Google Scholar. All titles andabstracts were checked to identify relevant articles. An article was considered eligible if it metfollowing inclusion criteria: (1) participants had to be human adults (> 18 years) diagnosed withidiopathic non-traumatic chronic (present for at least 3 months) neck pain; (2) papers had to reportoutcomes related to CS; and (3) articles had to be full-text reports or original research (no abstracts,case-reports, reviews, meta-analysis, letters, or editorials).Results: Six articles were found eligible after screening the title, abstract and – when necessary –the full text for in- and exclusion criteria. All selected studies were case-control studies. Overall, resultsregarding the presence of CS were divergent. While the majority of patients with chronic traumatic neckpain (i.e. whiplash) are characterized by CS, this is not the case for patients with chronic idiopathic neckpain. The available evidence suggests that CS is not a major feature of chronic idiopathic neck pain.Individual cases might have CS pain, but further work should reveal how they can be characterized.Limitations: Very few studies available.Conclusions: Literature about CS in patients with chronic idiopathic non-traumatic neck pain is rare andresults from the available studies provide an inconclusive message. CS is not a characteristic feature ofchronic idiopathic and non-traumatic neck pain, but can be present in some individuals of the population.In the future a subgroup with CS might be defined, but based on current knowledge it is not possible tocharacterize this subgroup. Such information is important in order to provide targeted treatment.Key words: Central sensitization, hypersensitivity, chronic pain, neck pain, idiopathic, nontraumatic, pressure pain thresholds, review