Chronic nociplastic pain affecting the musculoskeletal system: clinical criteria and grading system

Abstract

1. Introduction The term “nociplastic pain” was introduced by the International Association for the Study of Pain (IASP) in 2017 as a third mechanistic pain descriptor in addition to nociceptive and neuropathic pain [15, IASP website https://www.iasp-pain.org/Education/Content.aspx?ItemNumber=1698]. Nociplastic pain is defined as “pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain.” The term is intended for both clinical and research usage to identify individuals in whom there is pain and hypersensitivity in regions with apparently normal tissues and without any signs of neuropathy.15 Although central sensitization is most likely a dominating mechanism in nociplastic pain conditions, the term nociplastic pain should not be regarded as synonymous with the neurophysiological term “central sensitization”.15 In addition, a contribution of peripheral sensitization cannot be excluded. The concept of nociplastic pain harmonizes with the current view that certain forms of chronic pain are better understood as conditions or diseases of their own, rather than symptoms of other underlying pathology or diseases.26 The latter is reflected in the ICD-11 classification of chronic pain into primary—pain as a disease—and secondary—pain as a symptom—26where most, if not all, of the primary pain subgroups consist of conditions with nociplastic pain. However, it must be recognized that the terms reflect different dimensions as “nociplastic” is a mechanistic term, whereas “primary pain” is a diagnostic concept. Chronic pain conditions such as fibromyalgia, complex regional pain syndrome type 1, and irritable bowel syndrome are examples of pain conditions, where nociplastic pain is typically present.15 These conditions have documented changes of nociceptive processing in the nervous system,12,17–19 thus precluding the classification of their pain as “pain of unknown origin” (idiopathic pain). The classifier “pain of unknown origin” should be reserved for patients with pain that cannot be designated as nociceptive, neuropathic, or, now, nociplastic and is a label awarded by exclusion. It is becoming increasingly understood that many individuals have pain states, wherein there is more than one pain mechanism present. For example, patients with lumbar disk herniations often suffer from a nociceptive pain in the back and neuropathic pain (radiculopathy) in the leg. Nociplastic pain can also co-occur with neuropathic and particularly with nociceptive pain mechanisms. The latter is highlighted by the note in the nociplastic pain definition stating that “patients can have a combination of nociceptive and nociplastic pain.” In fact, it seems as though having ongoing nociceptive pain is a risk factor for developing nociplastic pain because hypersensitivity is associated with longer duration of nociceptive pain,16,21 and high rates of nociplastic pain states, such as fibromyalgia, are seen in individuals with osteoarthritis, rheumatoid arthritis, and other nociceptive pain disorders.5,28 Given that hypersensitivity is often seen also in nociceptive pain,14,16,24 the clinician is faced with an unresolved problem, namely, when should a patient with nociceptive pain be classified as also having nociplastic pain? Research in nociplastic pain states has used sophisticated techniques to specifically identify the dysfunctions involved. Quantitative sensory testing may be useful for assessing temporal summation1 and conditioned pain modulation,30 whereas offset analgesia32 and functional neuroimaging can identify changes in cerebral pain processing.12 However, these techniques are not always available for use in clinical practice or even in all research settings. Thus, the need for clinical criteria for nociplastic pain was recognized by the IASP, and an IASP Terminology Task Force (TTF) was formed to develop clinically useful criteria for nociplastic pain. It was recognized that different sets of clinical criteria would most likely be required for nociplastic pain manifested in the musculoskeletal system and viscera. Therefore, the criteria presented in this article are designed for nociplastic pain manifested within the musculoskeletal system. The intention is that criteria for nociplastic pain perceived in the viscera will be defined by another IASP task force consisting of experts in visceral pain and presented in a future article. 2. Procedures and processes The objective was to use a consensus procedure within an expert group consisting of the IASP TTF, to define a set of clinically and research applicable criteria for nociplastic pain presented in the musculoskeletal system. From a preliminary draft of classification criteria proposed by the chair to initiate further discussions, each member of the IASP TTF, ie, the authors, was asked to present his or her own