Toward ICHD-4: Aligning ICHD and ICOP criteria for trigeminal autonomic cephalalgias and migraine

Dear Editor,

The International Classification of Orofacial Pain (ICOP) was published in 2020, giving more insight into the oral and facial pain diagnoses and complementing the International Classification of Headache Disorders, third edition (ICHD-3) (1,2). The ICHD-3 includes criteria for Trigeminal autonomic cephalalgias (TAC) and Migraine, while ICOP includes criteria for their orofacial counterparts, namely Trigeminal autonomic orofacial pain and Orofacial migraine. Between these two classifications, there are cases where it is unclear whether the classification systems should be applied separately or together. The ICHD-3 does not mention the possibility of TAC presenting in the orofacial region except (i) under Cluster headache comments section, it states that it “may spread to other regions”, and (ii) under Short-lasting unilateral neuralgiform headache attacks, it includes the possible presentation in “other trigeminal distributions”. It is not clear if “other regions” refers to the maxillary and mandibular branches of the trigeminal nerve or extends to extra-trigeminal territories. In addition, under Migraine without aura comments section, ICHD-3 mentions that “A subset of otherwise typical patients has facial location of pain, which is called facial migraine” without indicating the possibility of oral presentation. On the other hand, the ICOP criteria for Trigeminal autonomic orofacial pain and Orofacial migraine completely excludes pain presenting in the head. ICOP's criteria for these disorders state that “Orofacial pain otherwise meeting the criteria for any of the subtypes or subforms below, but accompanied by head pain, should be classified according to ICHD-3”. This makes the two classification systems mutually exclusive. However, while ICOP refers to ICHD in its criteria, the opposite is not true. To clarify this confusion, we suggest adding consistent comments under TAC and Migraine in the ICHD-4 indicating the possibility of facial and oral presentations.

The presentation of facial pain in TAC and migraine is not uncommon, with 10% of these patients reporting pain in the face or oral cavity (3). An exclusive orofacial presentation is rare in TAC and migraine (4,5). In most cases, facial pain presents with headache, and both presentations should be managed as one disorder. However, the predominance of symptoms varies among patients. Despite the co-occurrence of headaches and facial pain in patients with TAC and migraine, facial pain may be the predominant symptom or the chief complaint with some degree of spread into the head or V1 territory. The frequency of this presentation is about 27% in orofacial migraine and 21% in orofacial TAC (3). According to ICOP, these cases will be classified based on the ICHD-3 with a headache diagnosis. Adhering to the current classification systems in such cases risks diverting the clinician's focus from the oral and facial region, where the pain primarily manifests. This, in turn, may lead to missing common comorbidities or differential diagnoses that usually present in the same area and could impact the accuracy of diagnosis and treatment. For example, in orofacial TAC, comorbid temporomandibular disorders (TMD) as well as oral/dental pain were found to be prevalent (4). In addition, it has been established that migraine and TMD are strongly associated, and orofacial migraine is not an exception (6,7).

To better align ICHD-4 and ICOP-2, we propose classifying pain based on the anatomical location of the more severe, more frequent or predominant symptoms. We used the definition of facial pain suggested by Ziegeler and May (8) to aid a more robust classification of orofacial TAC and migraine. Migraine and TAC should be classified according to ICOP and considered to be orofacial pain when pain that is more severe, more frequent, or considered by the patient as the chief complaint is located below the infra-orbitomeatal line, anterior to the pinnae, and above the neck. Otherwise, it should be classified according to ICHD. In cases where pain presents equally in the face/oral cavity and the head, both diagnoses of orofacial pain and headache should be given. In addition, ICOP already includes ICHD in its last criterion of corresponding diagnoses (e.g., Orofacial migraine). Therefore, we propose including ICOP to the last criterion of ICHD diagnoses to become “Not better accounted for by another ICHD or ICOP diagnosis”. Ruling out orofacial pain in headache diagnosis is important because many ICHD diagnoses such as Trigeminal neuralgia can mimic dental, oral, or musculoskeletal pain (e.g., cracked tooth syndrome, myofascial pain of masticatory muscles, temporomandibular joint arthritis) (9). Another reason is that pain in some structures in the head (e.g., temporalis muscle) that are supplied by the maxillary or mandibular branches of the trigeminal nerve can be deemed as orofacial pain according to ICOP (e.g., Orofacial myofascial pain). In this case, rather than just giving a headache diagnosis such as Tension-type headache, TMD risk factors should be assessed, and proper TMD management should be provided. In many cases, headache and orofacial pain are concurrent primary disorders and must be co-managed, and in other cases, one is secondary to the other, and only the primary disorder should be addressed.

The advantages of this proposed approach are that (i) it makes the diagnosis given more relevant to the patient's chief complaint. Using the current criteria, a patient that presents with severe facial pain that is accompanied sometimes with a mild headache will get diagnosed with a headache disorder rather than orofacial pain; (ii) it encourages multidisciplinary care. Following the previous example, getting an orofacial diagnosis instead will encourage consultations with ear, nose, and throat and orofacial pain specialists to rule out other causes of pain or rule in other comorbid pain conditions optimizing pain diagnosis and management; (iii) it facilitates communication among clinicians and improves the quality of retrospective research. Future research is encouraged to investigate the pathophysiological relationship between migraine, TAC, and their orofacial counterparts and the nature of pain comorbidity in the oral, facial, and head region.

Given the significant clinical and anatomical overlap between headache and orofacial pain disorders, it is essential that ICHD and ICOP work toward greater alignment. While each system brings with it a distinct history and clinical purpose, their current separation creates diagnostic ambiguity in cases where pain affects both facial and head regions. While a fully unified classification system may not be immediately feasible due to differences in disciplinary focus, a more integrated approach is both necessary and realistic. This would include reciprocal cross-referencing between ICHD and ICOP, matched diagnostic criteria for overlapping syndromes, and shared definitions of anatomical boundaries. Such integration would improve diagnostic accuracy, facilitate multidisciplinary care, and support more coherent research efforts across neurology, dentistry, and pain medicine.