International Classification of Headache Disorders

The third edition of the International Classification of Headache Disorders (ICHD-3) has now been published.1Headache Classification Committee of the International Headache SocietyThe International Classification of Headache Disorders.Cephalalgia. 2018; 38 (3rd edition): 1-211Crossref PubMed Scopus (1211) Google Scholar This classification and the corresponding diagnostic criteria were initially released as a beta document in 2014; since then, they have been widely accepted and should now form the basis of all diagnosis and management of headache disorders in clinical practice as well as in research. The ICHD-3, like its predecessors, is hierarchical and allows diagnosis in different clinical settings, diagnosing at the first or second level in general practice and at the third, fourth, or fifth level in neurological practice or in headache centres. The ICHD-3 contains a substantial amount of new information, but several updates in particular merit attention. New diagnostic criteria have been included for migraine with aura that better distinguish it from transient ischaemic attacks; the sub-forms include, for example, familial hemiplegic migraine at the fourth and fifth level. Chronic migraine, which was in the appendix of previous versions, has now been included in the main body of the classification. The sections on tension-type headache and trigeminal autonomic cephalalgia are largely unchanged. The diagnostic criteria for primary cough headache, primary exercise headache, primary headache associated with sexual activity, primary thunderclap headache, primary stabbing headache, nummular headache, hypnic headache, and new daily persistent headache have all been revised on the basis of new data. The secondary headaches have also been revised according to new general criteria. Importantly, the new classification allows diagnosis before the causative disorder has been treated; former editions of the classification required treatment of the causative disorder and relief of headache before a diagnosis could be made. Headache attributed to cranial or cervical vascular disorders includes a new entity: headache attributed to reversible cerebral vasoconstriction syndrome manifested by repeated thunderclap headaches. The ICHD-3 now recognises that headache attributed to arterial dissection and headache attributed to ischemic stroke can be acute as well as persistent (defined as lasting 3 months or more). Headache attributed to idiopathic intracranial hypertension and headache attributed to low cerebrospinal fluid pressure have revised criteria. The very important medication overuse headache—which occurs in 2% of the population2Westergaard ML Munksgaard SB Bendtsen L Jensen RH Medication-overuse headache: a perspective review.Ther Adv Drug Saf. 2016; 7: 147-158Crossref PubMed Scopus (22) Google Scholar and is probably the most widespread iatrogenic problem—is now simply defined as headache occurring 15 or more days per month and with medication overuse lasting at least 3 months, but a close temporal relation between headache and overuse is no longer required because such a relation is difficult to establish. If patients have chronic migraine and medication overuse, then both of these diagnoses should be applied. Previously, medication overuse precluded a diagnosis of chronic migraine. Headache attributed to aeroplane travel—a distinct severe headache that usually occurs at descent and disappears quickly after landing—has been recognised for the first time. Cervicogenic headache and headache attributed to temporomandibular disorder remain controversial because the borderland between them and tension-type headache is not distinct; few scientific studies have been done and there is disagreement between experts. A joint committee between the International Association for the Study of Pain and the International Headache Society has classified trigeminal neuralgia into classical with severe neurovascular contact, secondary, and idiopathic, and has developed revised diagnostic criteria that are included in the ICHD-3. The last section of the ICHD-3 includes the possibility to code for headaches of a presumed new type and for headache for which insufficient clinical information is available. The new classification is available in English1Headache Classification Committee of the International Headache SocietyThe International Classification of Headache Disorders.Cephalalgia. 2018; 38 (3rd edition): 1-211Crossref PubMed Scopus (1211) Google Scholar and is expected to be translated into more than 20 languages. The next and fourth edition of the International Classification of Headache Disorders is not expected until 10 years from now, so it is important for every neurologist to be familiar with the ICHD-3. I declare no competing interests.