1. Background on chronic headache and orofacial pain
Headache and orofacial pain (OFP) disorders are among the most prevalent pain disorders.26,47 Migraine is rated as the sixth most disabling disorder as measured by years lost due to disability.18 Combined with medication-overuse headache, headaches rank third (behind back pain and depression) among the disorders leading to disability.18 Orofacial pain disorders affect over a quarter of the population and induce significantly reduced quality of life and disability.43 These data establish a clear justification for a specific place of these disorders within the International Classification of Diseases (ICD).
Headache and OFP disorders are separated into primary (idiopathic) and secondary (symptomatic) types. Most research in the past decades centred on primary headache disorders, in particular on migraine. Only limited knowledge is available on the epidemiology and pathophysiology of secondary headache disorders. One reason for this may be that research has focused on the underlying disorder but not on the headache itself, despite the fact that some local or systemic disorders are mainly or exclusively characterized by their headache (eg, changes in intracranial pressure). Research on OFP, both primary and secondary, has lagged behind headache research possibly also due to a lack of a clear classification system.
Another way of subclassifying headache and OFP disorders is according to their temporal patterns.5,21 Although primary headache disorders are chronic in the sense that they can occur lifelong in an individual patient, another definition is needed for chronic secondary headache or OFP disorders as intended in this article. The term “chronic daily headache” was commonly used for headache disorders that occurred (untreated) on at least 50% of the days for at least 3 months and lasted at least 4 hours per day. The criterion of a minimum duration per day (2h for other conditions such as migraine in children) was used to exclude the paroxysmal headache disorders (eg, cluster headache) because these headache disorders are not really a chronic pain condition but a disorder of recurrent brief pain paroxysms. To create consistency across the classification, we now chose a minimum duration of 2 hours for all chronic secondary headaches. This way, chronic headache and OFP disorders can be separated from episodic (other terms would be paroxysmal or remitting) disorders by their time pattern.
Facial pain has generally been separated from headache because this type of pain is mostly musculoskeletal and transmitted through the second and third trigeminal branches, whereas headache disorders are transmitted through the first trigeminal branch. The academic definition of headache vs facial pain is anatomic. Headache is defined as pain occurring only or mainly above the orbitomeatal and/or nuchal ridge, whereas facial pain is defined as pain occurring mainly or exclusively under the orbitomeatal line, anterior to the pinnae and above the neck21; others include the forehead as part of the face.38 Nevertheless, the complex pain referral patterns to adjacent structures are so common that, in clinical practice, headache and facial pain are most often intimately related. In addition, we are specifically dealing with pain occurring within the oral cavity and thus relate to oral and facial pain as an entity termed OFP. Physicians typically have limited knowledge about oral pathology because this field generally has been delegated to dentistry. One of the aims of this article is to provide a chronic pain classification that can be used by both professions for the benefit of their patients.
2. The need for a classification system
The universally recognized International Classification of Diseases describes itself as “the foundation for the identification of health trends and statistics globally, and the international standard for reporting diseases and health conditions.”52 The ICD has established itself as the classification standard for clinicians and researchers alike. The ICD comprehensively brings together, under one hierarchical system, all known diseases, disorders, injuries, and other related health conditions. It is largely designed in a systems-based format that mostly disregards whether or not pain is present. Headache is part of ICD-10 in the Neurology chapter (G43 and G44), but acute and chronic as well as primary and secondary headache are not differentiated systematically. Orofacial pain is not represented in a separate chapter but mainly attributed to the anatomic basis of the pain (eg, trigeminal neuralgia is listed as subtype of trigeminal nerve disorders), and temporomandibular disorders (TMDs) are coded in 2 separate sections (G44.846 and K07.6). The diagnosis of headache has been largely guided by the International Classification of Headache Disorders (ICHD), which was established in 198820 and is now available in its third edition (ICHD-3).21 However, although ICHD is very detailed with respect to headache disorders, it fails to include some of the OFP disorders (including dental pain).4
Thus, a complete and comprehensive structure for pain in general, and headache and OFP in particular, is lacking. These gaps are obstacles to the collection of accurate data on important and common headache and OFP disorders. For pain clinicians and researchers, the current ICD is a very complex system to use and for this reason a new classification system was initiated.
3. The IASP task force ICD-11 initiative
To create a consistent classification of chronic pain, the International Association for the Study of Pain (IASP) established a task force that worked in close cooperation with World Health Organization (WHO) representatives, the International Headache Society (IHS), the IASP special interest group on orofacial and head pain (OFHA-SIG), the American Academy of Orofacial Pain, and the International Network for Orofacial Pain and Related Disorders Methodology (previously International RDC/TMD Consortium Network). This classification is dedicated exclusively to chronic pain syndromes and excludes acute pain. Chronic pain was defined as persistent or recurrent pain lasting longer than 3 months.49 This definition was chosen because it provides a clear operationalization that is in line with widely used criteria and includes the majority of relevant conditions. Applying this criterion to headache and OFP is more challenging because many disorders are episodic but recurrent in nature over long periods. For this reason, the concept of chronicity in headache and OFP includes a measure of attack frequency. Chronic headache is therefore defined as occurring for at least 2 hours per day on at least 50% of the days for more than 3 months and fulfilling criteria for the specific headache or OFP. This concept has been tested in OFP5 but has not yet been implemented fully.
The third edition of ICHD21 served as the starting point for the present classification and is extensively referenced for its definitions. ICHD-3 relies on a well-researched collection of pain-related data (location, severity, quality, referral etc.) and the selective use of special tests (neurophysiology, imaging etc.) to define specific disorders. However, some OFP disorders are still not specifically described, notably dental pain, different types of TMDs, and isolated facial presentations of resembling migraines and trigeminal autonomic cephalalgias (TACs).4,53 For TMD, the Diagnostic Criteria for Temporomandibular Disorders (DC-TMD) were adopted.41 The current proposal for chronic secondary headache and OFP disorders strives to close some of the gaps outlined above by adopting, together with ICHD-3, the DC-TMD and the proposals from the OFHA-SIG. The proposed classification underwent initial field testing in Australia, Germany, Japan, and Norway in 2016. Revised models were subjected to further testing through the website. We will report the results of these field tests separately.
The proposed classification is now part of the so-called “foundation layer” of ICD-11, which contains all diagnostic entities (diseases, disorder, signs, symptoms, etc.) with definitions as well as inclusion and exclusion criteria. These entities are hierarchically interconnected as a network of “parents” and “children”. In contrast to previous editions, ICD-11 allows “multiple parenting”, ie, any given entity (“child” or “subordinate”) may belong to more than one major section (“parent”). This is exemplified by trigeminal neuralgia (child/subordinate) being assigned to both the peripheral neuropathic pain and the headache/OFP categories (parents).
In the proposed classification of chronic pain, extension codes will allow to specify the time course and severity of the pain as well as the presence of psychological and social factors.48 Pain severity is a combined score of pain intensity, pain-related distress, and functional impairment that are quantified using standardized rating scales; functioning properties will, in addition, be specified according to the International Classification of Functioning, Disability and Health (ICF).35
For the actual diagnostic coding, the WHO prepares subsets from the foundation, the so-called “linearizations.” The most important linearization is the Mortality and Morbidity (MMS) Linearization. It is the basis of the statistical reporting of mortality data by WHO member states; it is also used for reimbursement purposes in many health systems worldwide and for morbidity statistics. The current version was “frozen” (June 18, 2018) in preparation for its implementation by the member states from 2022 onwards.
4. Classification of chronic secondary headache or orofacial pain
4.1. General structure of the chronic pain classification: chronic primary and secondary headache or orofacial pain disorders
Chronic headache or OFP was split into 2 main domains: (1) chronic primary headache or OFP and (2) chronic secondary headache or OFP. A similar distinction was made for chronic visceral pain and for chronic musculoskeletal pain.2,36 The term “primary” was preferred over “idiopathic” because we often understand the pathophysiological events underlying some of these disorders. Chronic secondary headache or OFP is defined as headache or OFP that occurs on at least 50% of the days during at least 3 months and lasting at least 2 hours per day, and is clearly associated with the effects of disease (regional or systemic), trauma (physical, chemical, radiation), infection, or a host of other factors. The entities covered are shown in Table 1 together with ICD-10 counterparts, where those exist. In this article, we highlight the more novel aspects of the classification and the reader is referred to the existing and widely accepted classifications for all other entities (ICHD-3 and DC-TMD).
Chronic primary headache and OFP disorders are described separately in a different article published by the same working group.34 However, to give an insight into the primary headache and OFP disorders, these conditions are briefly described as follows.
4.1.1. Chronic primary headache
Chronic primary headache is defined as headache that occurs on at least 15 days per month for more than two hours per headache day for more than 3 months. Chronic primary headache disorders are mostly a continuation of their episodic counterparts such as chronic migraine, chronic tension-type headache, and new daily persistent headache. The chronic counterparts of the TACs include chronic cluster headache, chronic paroxysmal hemicrania, and short-lasting unilateral neuralgiform headache attacks. Of note, chronicity in TACs is defined as headache attacks occurring for more than 1 year without remission, or with remission periods lasting less than 3 months. Hemicrania continua, one of the TACs, is a chronic disorder by definition.
4.1.2. Chronic primary orofacial pain
Orofacial pain, of which about 10% is chronic, affects around a quarter of the general population.28,31,33 This is in agreement with the 2009 National Health Interview Survey that found that 5% of adults reported pain in the face or jaw over a 3-month period.39 The incidence ratio of persistent facial pain was reported at 38.7 per 100,000 person years, is more common in women, and increased with age.26 Most chronic primary OFP is associated with a painful TMD, which is quite prevalent. Almost 5% of the population report this type of pain (6.3% in women, 2.8% in men).22 Other diagnoses in this section include burning mouth syndrome and atypical facial pain.
4.2. Chronic secondary headache or orofacial pain
In ICHD-3, secondary (or symptomatic) headache disorders are the consequence of an underlying disorder or dysfunction. Causation is mainly established by a temporal link and by typical patterns of headache. Causation is not always indisputable; so, the term “attributed to” is used to explain the link between the underlying disorder and headache. The same logic is applied here to chronic secondary OFP disorders.
The secondary headache and OFP disorders are listed in the order of ICHD-3 and explained using the terminology of ICHD-3. This means that every chapter of the ICHD-3 relating to chronic secondary headache disorders is represented in the ICD-11 classification. Chapter 12 of ICHD-3 (headache attributed to psychiatric disorders) was omitted because there is not enough evidence that a specific chronic secondary headache exists that is caused by psychiatric disorders. Chapter 13 of ICHD-3 was modified so that individual sections are now assigned to chronic dental pain and to facial pain and/or headache attributed to TMD. The remaining sections in chapter 13 of ICHD-3 comprise the neuropathic OFP disorders, in particular trigeminal neuralgia and other disorders of the trigeminal nerve. The organisation of chronic secondary headache or OFP is presented in Figure 1.
4.2.1. Chronic headache or orofacial pain attributed to trauma or injury to the head and/or neck
Posttraumatic headache and OFP are common secondary pain disorders. As per accepted definition, “acute” refers to those occurring during the first 3 months after such a traumatic event. “Chronic or persistent posttraumatic headache/OFP” is used if the pain continues beyond that time. Most often, posttraumatic headache/OFP resembles the primary version such as tension-type headache or migraine. The diagnosis, therefore, depends on the establishment of an association between the trauma or injury and the headache/OFP onset. To establish a strict diagnosis of posttraumatic headache/OFP pain, it must manifest itself within 7 days after trauma or injury, or within 7 days after regaining consciousness, and/or within 7 days after recovering the ability to sense and report pain. The 7-day interval is somewhat random, with some experts proposing that the onset of posttraumatic headache may occur after a longer interval. However, this longer interval is observed only in a minority of patients and there are insufficient published data to change this criterion.3
Headache and OFP may occur as the sole complaint after trauma or injury. In some patients, pain is accompanied by further symptoms, such as dizziness, fatigue, reduced ability to concentrate, psychomotor slowing, mild memory problems, insomnia, anxiety, personality changes, and irritability. A patient presenting with this constellation of symptoms after head injury would receive the diagnosis “postconcussion syndrome.”50 Depending on the location of the initiating trauma, OFP may be comorbid or the leading symptom.6
4.2.2. Chronic headache or orofacial pain attributed to cranial or cervical vascular disorder
Relevant cranial or cervical vascular disorders that can cause chronic headache include ischemic stroke, nontraumatic intracranial hemorrhage, unruptured vascular malformation, arteritis, cervical carotid or vertebral artery disorder, other acute intracranial arterial disorders, genetic vasculopathy, and pituitary apoplexy. Cervical artery dissections most commonly present with head, face, or neck pain that is sometimes accompanied by other signs. This presentation occurs in up to 95% of internal carotid artery dissections and in 70% of vertebral artery dissections.8,9,14,19,32,45 In internal carotid artery dissections, a unilateral headache may be the single symptom in 45% of cases. It is ipsilateral to dissection with a steady or throbbing quality.17,32 A typical case is shown in Case vignette 1 (chronic headache after subarachnoid hemorrhage).24 Here, the chronic headache appeared despite successful surgical management of the hemorrhage; it had different characteristics than the initial “thunderclap” headache and was resistant to treatment.
chronic secondary headache disorder: chronic headache attributed to subarachnoid hemorrhage Cited Here...
A 59-year-old woman complains of bilateral frontotemporal headache. The pain is dull and pressing and is present every day for at least 6 hours. Pain severity is largely moderate (visual analogue scale 5-6 on a 0-10 scale) but exacerbations occur by psychosocial stress and by Valsalva's maneuver. There are no accompanying symptoms with this headache.
The headache started after a subarachnoid hemorrhage (SAH) that she had in the age of 57. The SAH started with an extreme thunderclap headache, after which the patient had amnesia for about 2 weeks. An intracranial bleeding due to a large aneurysm was detected, and a craniotomy was performed for clipping of the aneurysm. The patient was in coma for 10 days. After awakening from the coma, the patient experienced a dull headache, which she never had before. There were no other sequelae from the SAH. Treatment with amitriptyline 25 mg in the evening had a positive impact on headache intensity but the headache is not cured. The headache cannot be modulated by any other therapies such as physiotherapy or biofeedback.
Vascular conditions causing headache/OFP have an acute presentation, typically display neurological signs, and often remit rapidly.21 A close temporal relationship between the manifestation of the headache/OFP and the neurological signs is central to establish causation. If it is present, a diagnosis can be relatively straightforward.
Many of the vascular conditions such as ischemic or hemorrhagic stroke present with dramatic symptomatology, such as disorders of consciousness and severe focal neurological signs that overshadow the headache. Conversely, headache is the prominent presenting symptom in other conditions such as subarachnoid hemorrhage. Acute-onset headache may be an initial warning sign in ominous, and often life-threatening, conditions such as dissections, cerebral venous thrombosis, giant cell arteritis, and central nervous system angiitis. Clearly, early diagnosis of such presentations is crucial and allows for appropriate interventions aimed at the underlying vascular disease that may prevent devastating neurological consequences.
Because primary headaches are extremely common, these conditions often occur in patients who report a history of headache. Nevertheless, headache associated with vascular conditions is characterized by a sudden onset of a novel type of headache, usually not familiar to the patient. In these situations, the presence of vascular conditions should be suspected.21
4.2.3. Chronic headache or orofacial pain attributed to nonvascular intracranial disorder
Relevant nonvascular intracranial disorders include increased cerebrospinal fluid pressure, low cerebrospinal fluid pressure, noninfectious inflammatory intracranial disease, intracranial neoplasms, intrathecal injection, epileptic seizure, Chiari malformation type I, and other nonvascular intracranial disorders.16 Compared to those on primary headaches, there are few epidemiological studies of these headache types. Controlled trials of therapy are almost nonexistent. Similarly, chronic OFP, usually with neurological signs, will result from nonvascular intracranial disorders such as neoplasms.7,11,27,37,40
4.2.4. Chronic headache attributed to a substance or its withdrawal
Potential etiologies include exposure to a substance as in medication overuse headache (ergotamine, triptans, simple analgesics, compound analgesics, opioids, and others) or substance withdrawal (caffeine, estrogen, and other substances with long-term use). Migraineurs seem to be physiologically hypersensitive to a variety of stimuli. Alcohol, certain foods and additives, chemical and drug ingestion and their withdrawal have been implicated in the provocation of a migraine attack in predisposed individuals.12,29 There is also a suspicion that migraneurs are psychologically hyperresponsive to relevant stimuli and challenges such as stress and anxiety.
Associations between headache and substance use or withdrawal are often anecdotal, many based on reports of adverse drug reactions. The association of a substance with headache does not establish causation; so, the clinician must consider other etiologies. Headache onset and substance exposure may be merely coincidental, particularly regarding substances that are consumed extremely commonly (eg, cheese). In addition, headache may be the symptom of a systemic disease that necessitates pharmacotherapy and the drugs may be mistakenly blamed for the headache. Furthermore, drug trials, in particular for episodic migraine, list adverse drug reactions that include typical signs and symptoms of the disorder itself. In the case of migraine trials, these include headache, nausea, and other associated symptoms. Some disorders may predispose to drug-related headache: alone, neither the drug nor the condition would produce headache.21
4.2.5. Chronic headache or orofacial pain attributed to infection
Intracranial infections that can cause chronic headache or OFP include bacterial meningitis or meningoencephalitis, viral meningitis or encephalitis, intracranial fungal or other parasitic infections, and brain abscess or subdural empyema.1 Relevant systemic infections may be caused by bacteria, viruses, or other organisms.15 Headache is usually the consequence of active infection, resolving within 3 months of eradication of the infection, and therefore would not be considered a chronic headache. When the infection cannot be eliminated and remains active, headache may persist, and if it continues for 3 months or longer, it is considered chronic. More rarely, the infection resolves or is eradicated but headache persists nevertheless. Then, similarly, it is considered chronic if it lasts longer than 3 months.
Headache is the first and most commonly encountered symptom in patients with intracranial infections. Report of a novel diffuse headache associated with a variable combination of the following symptoms should direct attention towards an intracranial infection even in the absence of neck stiffness: focal neurological signs and/or an altered mental state and a general malaise and/or pyrexia.46
4.2.6. Chronic headache or orofacial pain attributed to disorders of homeostasis or their nonpharmacological treatment
This comprises all chronic headache disorders caused by disorders of homoeostasis including hypoxia and/or hypercapnia (ie, high altitude, aeroplane travel, diving, and sleep apnea), dialysis, arterial hypertension, hypothyroidism, fasting, and cardiac cephalalgia. The diagnosis is also appropriate when chronic pain is attributed to their nonpharmacological treatment; if it is attributed to pharmacological treatment, the section 4.2.4. applies. Orofacial pain may occur together with such headaches or in isolation. Cardiac cephalgia that accompanies chest symptoms has been reported in 5.2% of one series of patients with myocardial infarction (MI).4,13 More rarely, MI pain may be “isolated,” presenting primarily as headache (3.4%), jaw pain (3.6%), or neck pain (8.4%).4 Interestingly, there seems to be an anatomical correlate between pain location and site of infarct, with inferior MI associated with OFP (8.3%) and cardiac cephalgia more frequently reported (7.3%) in anterior MI.4,13
4.2.7. Chronic headache or orofacial pain attributed to disorders of cranium, neck, eyes, ears, nose, sinuses, teeth, mouth, or other facial or cervical structures
The cervical spine and other neck structures have been associated with chronic headache or OFP. Clinically, many headaches and OFP seem to refer from cervical, nuchal, or occipital regions. Many of these have been attributed to cervical osteodegenerative changes. However, virtually all people older than 40 years have some degree of cervical degenerative pathology.30,44 Large-scale controlled studies clearly show that people with and without headache or OFP have similar prevalences of cervical degenerative changes. Spondylosis or osteochondrosis are therefore not conclusively the explanation of associated headache or OFP. Other widespread disorders suspected to underlie chronic headaches and OFP, such as chronic sinusitis, TMDs, and refractive errors of the eyes, have also been shown to be equally prevalent in patient and control populations.
In establishing the diagnosis of chronic secondary headache or OFP, the rules for causation need to be more rigorously applied. These include the establishment of the strength, consistency, specificity, and temporal sequence of the association in addition to its biological coherence, gradient, and plausibility within current medical knowledge.10 Experimentation with the treatment of the suspected disease and observation of outcomes are essential. With these, better classification criteria may emerge.
4.2.8. Chronic dental pain
Chronic dental pain results from a disorder involving the teeth or associated tissues (pulpal, periodontal, or gingival pain). The typical causative factor will be caries or trauma to a tooth or teeth or associated tissues. In addition to clinical examination, imaging (intraoral x-rays, computed tomography scans etc.) may facilitate the correct diagnosis.
Untreated dental decay has been reported as the most important reason for toothache, which can impact routine daily activities. Toothache is a common problem and, depending on geographic location, may be highly prevalent.23 However, it is unclear what proportion of reported toothache is truly chronic and more data are needed.25 From currently available data, duration of constant toothache is present for 27.6 days up to seeking care.25 A similar study estimated 55.2 days of tooth pain before presenting for treatment to an emergency dental clinic.51 However, as the above epidemiology suggests, truly chronic (ie, lasting >3 months) dental pain may be extremely rare and caution should be exercised when diagnosing such cases. If the etiology is vague and examination/testing is inconclusive, consider whether diagnoses in the section of chronic primary pain may be more suitable.34
4.2.9. Chronic neuropathic orofacial pain
This chapter comprises painful lesions or diseases of the cranial nerves and is also part of the section on chronic neuropathic pain.42 The existing nosology of cranial nerve pains is not totally satisfactory as discussed in the respective companion paper.42 Many long-established diagnostic terms, which may be strictly inaccurate, have been retained (trigeminal neuralgia and other less frequent cranial neuralgias). ICHD-3 presents detailed definitions, subtypes, and subforms.21
4.2.10. Chronic secondary temporomandibular disorder pain
Chronic secondary TMD is chronic pain in the temporomandibular joint(s) or masseter or temporalis muscle(s) attributed to persistent inflammation (due to eg, infection, crystal deposition or autoimmune disorders), structural changes (such as osteoarthritis or spondylosis), injury, or diseases of the nervous system. It occurs for at least 2 hours per day on at least 50% of the days during at least 3 months. If the etiology is vague, consider using codes in the section of chronic primary pain.34 Chronic secondary TMD pain should be subtyped as myofascial TMD pain or temporomandibular joint arthralgia, or both. A typical case is illustrated in Case vignette 2.
chronic secondary orofacial pain disorder: secondary temporomandibular joint disorder Cited Here...
A 45-year-old woman complains of bilateral pain around the temporomandibular joints (TMJs) during chewing and yawning. The pain is sharp and shooting with spread to the temporal region and ear. The pain is present more than 2 hours per day and has lasted for more than 6 months. During the jaw movements, pain intensity is rated high with a visual analogue scale score of 7 to 8 (on a 0-10 scale) and at rest intensity is mild with a visual analogue scale score of 2 to 3. The TMJ is painful on standardized palpation at and around the lateral pole of the TMJ. Furthermore, there is crepitus in the TMJ during open–close movements. In addition, the masseter and temporalis muscles are painful on palpation. Intraoral examination reveals an anterior open bite and tooth contacts only at the molar teeth. A computed tomography scan reveals severe degenerative changes on the condyle and fossa with resorption, osteophyte formation, and subchondral cysts. The patient reports several previous episodes of significant TMJ pain lasting up to 1 year. She also has an underlying diagnosis of rheumatoid arthritis (7 years) and is currently being treated with methotrexate. For her flare up of TMJ pain, she is treated with arthrocentesis, which results in significantly decreased TMJ pain. Additional therapy includes a hard occlusal splint and physiotherapy.
4.2.11. Other specified and unspecified chronic secondary headache or orofacial pain
Diseases not explicitly listed in the classification may be captured in a residual category for “Other specified chronic headache or orofacial pain”; an additional category for unspecified conditions will provide for the classification of disorders for which insufficient information is available to assign a more precise diagnosis. These residual categories are automatically added by WHO.
The systematic classification of chronic secondary headache and OFP disorders as presented in this article is intended both for clinical and for research purposes. These chronic secondary pain codes should be used when the headache or OFP can be attributed to an underlying cause; the underlying cause should be coded as well.48 In combination with the extension code for pain severity, this will serve the purpose of identifying those patients whose pain needs specialist care. As demonstrated in the Case vignette 1, chronic pain may outlast the initiating event and may become the leading cause for continuing treatment need. This pattern is also known for other chronic secondary pain syndromes, eg, in chronic osteoarthritis.36
Within the classification of chronic pain for ICD-11, diagnostic categories are relatively broad. For further differentiation of chronic secondary headache disorders, ICHD-3 provides more sophisticated and detailed classification criteria that can be used if necessary. However, the present classification is more detailed in orofacial and dental pain disorders as some of these disorders are not considered or only mentioned briefly (eg, TMD) in ICHD-3. Thus, chronic secondary OFP syndromes are categorized here for the first time in a systematic manner.
For research purposes, this classification is aimed to stimulate clinical studies on the characteristics and on the treatment of chronic secondary headache disorders and OFP. These disorders have been neglected in clinical research in the past, mainly due to a low interest of the major research groups. If distinct subgroups of chronic secondary headache and OFP disorders are enrolled in studies or clinical trials, this classification is recommended. Furthermore, this classification system is intended to create awareness of chronic secondary headache and OFP syndromes. In many cases, the clinical picture of the pain in the disorders presented in this article is similar to that of chronic primary headache disorders. This often leads to a misdiagnosis of secondary headaches, which are then simply diagnosed as chronic tension-type headache.
This classification is mainly based on the clinical phenotype of the underlying disorder causing the headache or OFP. In the future, other principles may be the basis for a new classification. For example, the pathophysiological mechanisms of the pain signaling itself are poorly understood in secondary (symptomatic) headache or OFP. New knowledge of these mechanisms could lead to a novel systematic classification. Another example for a future classification could be differential responses to multimodal pain treatment. Although it is natural to treat the chronic secondary headache or OFP by treating the underlying disorder, this is not possible in all cases. So, the response to different pharmacological treatments or nonpharmacological procedures could help in grouping these headache and OFP disorders. This would be a pragmatic approach to determine the level of granularity required in diagnostics: if all chronic secondary headaches and OFP disorders were responsive to the same (combination) therapy, further subclassification would only serve academic and epidemiological purposes. Given the diverse nature of the underlying conditions, we find this highly unlikely and anticipate that with research progress, individual patients also will benefit from more sophisticated treatment algorithms.
Finally, it should be acknowledged that this classification system of chronic secondary headache and OFP disorders has been developed and accepted in close cooperation of the 2 major scientific societies that are focused (among others) on these disorders, namely IASP and IHS. This is the first cooperation of its kind and will help to increase acceptance and use of this classification.
6. Summary and conclusions
This article presents a novel classification of chronic secondary headache and OFP disorders as agreed by the 2 major scientific societies in this field (IASP and IHS). It is part of the project to classify chronic pain syndromes for the upcoming ICD-11. Although most of the chronic secondary headache syndromes are grouped and classified according to ICHD-3, the OFP syndromes as presented here are grouped by different systems including ICHD-3, DC-TMD, and proposals by OFHA-SIG. This classification should help to better diagnose these disorders and to stimulate research.
Conflict of interest statement
R. Benoliel has nothing to disclose. P. Svensson has nothing to disclose. S. Evers has nothing to disclose. S.-J. Wang reports personal fees from Eli-Lilly, personal fees from Daiichi-Sankyo, grants and personal fees from Pfizer, Taiwan, personal fees from Eisai, personal fees from Bayer, and personal fees from Boehringer Ingelheim, outside the submitted work. A. Barke reports personal fees from IASP, during the conduct of the study. B. Korwisi has nothing to disclose. W. Rief reports grants from IASP, during the conduct of the study; personal fees from Heel and personal fees from Berlin Chemie, outside the submitted work. R.-D. Treede reports grants from Boehringer Ingelheim, Astellas, AbbVie, and Bayer, personal fees from Astellas, Grünenthal, Bauerfeind, Hydra, and Bayer, and grants from EU, DFG, and BMBF, outside the submitted work.
The authors gratefully acknowledge the financial support by the International Association for the Study of Pain (IASP) and the excellent discussions with Dr Robert Jakob of WHO.
Members of the Taskforce: Rolf-Detlef Treede (Chair), Winfried Rief (Co-chair), Antonia Barke, Qasim Aziz, Michael I. Bennett, Rafael Benoliel, Milton Cohen, Stefan Evers, Nanna B. Finnerup, Michael First, Maria Adele Giamberardino, Stein Kaasa, Beatrice Korwisi, Eva Kosek, Patricia Lavand'homme, Michael Nicholas, Serge Perrot, Joachim Scholz, Stephan Schug, Blair H. Smith, Peter Svensson, Johannes Vlaeyen, Shuu-Jiun Wang.
Supplemental digital content
Supplemental digital content associated with this article can be found at http://links.lww.com/PAIN/A658. SDC includes a complete reference list of the diagnoses entered into the foundation with the foundation IDs as well as the extension codes (specifier). Since the complete list is contained, the material is identical for all papers of the series.
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