In this volume of PAIN, the IASP Special Interest Group (SIG) on complex regional pain syndrome (CRPS) reports on their consensus to resolve questions and ambiguities in the IASP diagnostic criteria for CRPS,5 which were developed at a workshop during the 2019 EFIC congress in Valencia, Spain. This includes the consensus that CRPS is not a form of neuropathic pain and, therefore, should not be classified as a disease of the nervous system. Andreas Goebel et al. resolved ambiguities in the diagnostic text of the Budapest criteria4 concerning CRPS subtypes and diagnostic procedures, and they also submitted their consensus adaptation of CRPS as a chronic primary pain syndrome to the World Health Organization (WHO) for its inclusion in the prelaunch revision of the ICD-11 (see online supplement to Goebel et al.5). The article is remarkable for several reasons that make it interesting reading material for both clinicians and researchers.
First, this perspectives paper5 represents a culmination point of about 150 years of work on the clinical classification and pathophysiology of chronic pain conditions that are initiated by physical trauma but by far exceed the usual sequelae of such traumata: causalgia as described by Weir Mitchell in victims of gunshot wounds in the American Civil War10,11 and reflex dystrophy as described by Paul Sudeck in surgical patients at the Eppendorf University Hospital in Hamburg.16 For about a century, the autonomic nervous system was considered to play a key role in the pathophysiology of these 2 conditions, since René Leriche discovered the beneficial therapeutic effects of sympathectomy.9 The debate whether sympathetic hyperactivity or adrenoreceptor supersensitivity is more important has accompanied much of IASP's history.1,13,14 In the end, the concept of CRPS evolved as a syndrome with 4 dimensions,4 where the autonomic nervous system is involved in some of the clinical presentations, but sensory signs and symptoms are related more to neurogenic inflammation and central sensitization.2,15 These characteristics make CRPS a candidate syndrome for a contribution by nociplastic pain mechanisms8 and for classification as chronic primary pain.12
Second, the new concept of chronic primary pain (CPP: MG30.0 in the ICD-1121) is filled with more content. The new diagnosis CPP in the ICD-11, for the first time, provides a specific diagnosis for chronic pain syndromes that can be considered as a health condition in their own right.12,17 In previous revisions of the ICD (eg, ICD-10), chronic pain conditions that would now be classified as CPP were scattered among different chapters, which failed to reflect their status as health conditions in their own right. With the new ICD-11, these diagnoses can finally be classified adequately within the umbrella category of CPP.12 This concept had been inspired by the concept of primary headaches,7,17 and chronic migraine headache is one of its manifestations (linked in the ICD-11 from the headache chapter20,21). Several other diagnoses were relocated to CPP: fibromyalgia syndrome (FMS, previously placed within the chapter for soft-tissue disorders in the ICD-1019), chronic primary low back pain (formerly known as “nonspecific” low back pain and classed as a disease of the musculoskeletal system in the ICD-1019), and vulvodynia (linked in the ICD-11 from the chapter for diseases of the genito-urinary system3,18,22). Complex regional pain syndrome is yet another example for a chronic pain syndrome that could not be categorized appropriately before. As a heritage code from ICD-10, CRPS was located automatically in the respective ICD-11 chapter for focal or segmental autonomic disorders (8D8A.0).21 From this chapter, CRPS is linked to CPP through the ICD-11 principle of “double parenting”. According to this coding principle, CRPS in the ICD-11 inherited the common denominators of CPP (Box 1). This should now inspire clinicians and researchers to investigate commonalities and differences among CPP syndromes such as CRPS, FMS, chronic migraine, and others.
Third, this perspectives paper5 illustrates how the processes to maintain the content models of the ICD-11 operate at the WHO. The current primary coding for CRPS in the ICD-11 (8D8A) is considered obsolete, since it is based on an outdated pathophysiological view of CRPS. The consensus statement was sent to the WHO for amending the ICD-11 CRPS-related coding, and a respective proposal was uploaded to the ICD-11 development platform (online supplement to Goebel et al.5). This proposal suggests to move CRPS to CPP, which would entail changing its diagnostic code into an MG30.0 code.5 The IASP Task Force (TF) for the Classification of Chronic Pain has endorsed the proposal by the CRPS SIG, and it is also supported by the American Autonomic Society. The WHO has defined consensus and evidence as requirements for all diagnoses and entities included in the ICD-11.23 Evidence supporting the reclassification of CRPS as a CPP is provided in the perspectives paper by Goebel et al.5 Other liaison partners of the TF included the International Society of Physical and Rehabilitation Medicine as well as the IASP neuropathic pain SIG. The implementation of this proposal is currently under review by WHO's Classification and Statistics Advisory Committee.22 But, several corrections have already been implemented since the acceptance of ICD-11 by the World Health Assembly in 2019: Since January 2020, CRPS is no longer linked to MG30.5 chronic neuropathic pain,22 but it is linked to MG30.2 chronic postsurgical or post traumatic pain, which reflects the frequently initiating event in CRPS.
In their article, Goebel et al.5 express the wish to maintain continuity with the published and widely used CRPS Budapest criteria.4 However, this aim at continuity creates a dilemma: In the Valencia consensus, CRPS type II is characterized by pain that must extend beyond any nerve territory.5 Unfortunately, this is not at all reflected in the diagnostic criteria as presented in Table 1 of their article.5 This might lead to potentially misdiagnosing CRPS type II. Therefore, we argue that the harmonization of the CRPS diagnostic criteria has to be validated empirically as was performed for the original Budapest criteria.6
In conclusion, the article by Goebel et al.5 is a valuable contribution to the CRPS diagnostic literature, and it will help guide clinicians and researchers in the identification and treatment of these patients. The Valencia consensus5 and how it was implemented in the ICD-11 is an outstanding example for a fruitful cooperation and liaison initiative of 3 IASP groups (CRPS SIG, neuropathic pain SIG, and TF for the Classification of Chronic Pain) with other scientific societies and the WHO.
Conflict of interest statement
B. Korwisi reports other from IASP, outside the submitted work. The remaining authors have no conflicts of interest to declare.
Text box 1.
Definition of chronic primary pain
Chronic primary pain is defined as chronic pain (ie, persisting or recurring for longer than 3 months) that is:
- (1) Located in one or more anatomical regions;
- (2) Characterized by significant emotional distress (eg, worry and hopelessness) or functional disability (eg, inability to work due to the pain);
- (3) Not better accounted for by another diagnosis.
As any pain, chronic primary pain is multifactorial. Importantly, the diagnosis is appropriate independently of identified psychological or biological contributors.
Note: Definition as outlined in Nicholas et al.12 and implemented in the ICD-11 Browser.20,21
All authors are members of the IASP Task Force for the Classification of Chronic Pain.
. Baron R, Maier C. Reflex sympathetic dystrophy: skin blood flow, sympathetic vasoconstrictor reflexes and pain before and after surgical sympathectomy. PAIN 1996;67:317–26.
. Birklein F, Ajit SK, Goebel A, Perez RSGM, Sommer C. Complex regional pain syndrome - phenotypic characteristics and potential biomarkers. Nat Rev Neurol 2018;14:272–84.
. Bornstein J, Preti M, Radici G, Stockdale CK, Vieira-Baptista P. Vulvodynia: a neglected chronic pain diagnosis. PAIN 2019;160:1680–1.
. Bruehl S, Harden NR, Galer BS, Saltz S, Bertram M, Backonja M, Gayles R, Rudin N, Bhugra MK, Stanton-Hicks M. External validation of IASP diagnostic criteria for Complex Regional Pain Syndrome and proposed research diagnostic criteria. PAIN 1999;81:147–54.
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. Harden RN, Bruehl S, Perez RSGM, Birklein F, Marinus J, Maihofner C, Lubenow T, Buvanendran A, Mackey S, Graciosa J, Mogilevski M, Ramsden C, Chont M, Vatine J-J. Validation of proposed diagnostic criteria (the ‘Budapest criteria’) for Complex Regional Pain Syndrome. PAIN 2010;150:268–74.
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. Kosek E, Cohen M, Baron R, Gebhart GF, Mico J-A, Rice ASC, Rief W, Sluka AK. Do we need a third mechanistic descriptor for chronic pain states? PAIN 2016;157:1382–6.
. Leriche R. L'anesthésie isolée du ganglion étoile: sa technique, ses indications, ses résultats. Press Med 1934;42:849–50
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. Nicholas M, Vlaeyen JWS, Rief W, Barke A, Aziz Q, Benoliel R, Cohen M, Evers S, Giamberardino MA, Goebel T, Korwisi B, Perrot S, Svensson P, Wang S-J, Treede R-D. The IASP Taskforce for the Classification of Chronic Pain. The IASP classification of chronic pain for ICD-11: chronic primary pain. PAIN 2019;160:28–37.
. Raja SN, Treede RD, Davis KD, Campbell JN. Systemic alpha-adrenergic blockade with phentolamine: a diagnostic test for sympathetically maintained pain. Anesthesiology 1991;74:691–8.
. Roberts WJ. A hypothesis on the physiological basis for causalgia and related pains. PAIN 1986;24:297–311.
. Roberts WJ, Foglesong ME. Spinal recordings suggest that wide-dynamic-range neurons mediate sympathetically maintained pain. PAIN 1988;34:289–304.
. Sudeck P. Über die akute (trophoneurotische) Knochenatrophie nach Entzündungen und Traumen der Extremitäten. Dtsch Medizinische Wochenschrift 1902;28:336–8.
. Treede R-D, Rief W, Barke A, Aziz Q, Bennett MI, Benoliel R, Cohen M, Evers S, Finnerup NB, First MB, Giamberardino MA, Kaasa S, Korwisi B, Kosek E, Lavand’homme P, Nicholas M, Perrot S, Scholz J, Schug S, Smith BH, Svensson P, Vlaeyen JWS, Wang S-J. The IASP taskforce for the classification of chronic pain. Chronic pain as a symptom or a disease: the IASP classification of chronic pain for the international classification of diseases ICD-11. PAIN 2019;160:19–27.
. Treede R-D, Rief W, Korwisi B, Aziz Q, Giamberardino MA, Barke A. Reply to Bornstein et al. PAIN 2019;160:1681–83.
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