Editing Headache (section)

=== Classification ===
Headaches are most thoroughly classified by the [[International Headache Society]]'s International Classification of Headache Disorders (ICHD), which published the second edition in 2004.<ref name="IHS_ICHD2">{{cite book |url=http://ihs-classification.org/en/ |title=IHS Classification ICHD-2 |publisher=International Headache Society |edition=Online |url-status=dead |archive-url=https://web.archive.org/web/20131103104037/http://ihs-classification.org/en/ |archive-date=3 November 2013 |access-date=18 November 2013 }}</ref> The third edition of the International Headache Classification was published in 2013 in a beta version ahead of the final version.<ref>[//www.ichd-3.org/ ''Website The International Headache Classification (ICHD-3 Beta)'']. Retrieved 29. August 2016.</ref> This classification is accepted by the [[WHO]].{{sfn|Olesen et al.|2005|pages=9–11}}

Other classification systems exist.  One of the first published attempts was in 1951.<ref>{{cite journal | vauthors = Brown MR | title = The classification and treatment of headache | journal = The Medical Clinics of North America | volume = 35 | issue = 5 | pages = 1485–1493 | date = September 1951 | pmid = 14862569 | doi = 10.1016/S0025-7125(16)35236-1 }}</ref> The US [[National Institutes of Health]] developed a classification system in 1962.<ref>{{cite journal | journal = JAMA | author = Ad Hoc Committee on Classification of Headache | title = Classification of Headache | volume = 179 | pages = 717–8 | year = 1962 | doi = 10.1001/jama.1962.03050090045008 | issue = 9 }}</ref>

==== ICHD-2 ====
{{Main|International Classification of Headache Disorders}}
The [[International Classification of Headache Disorders]] (ICHD) is an in-depth [[hierarchical]] classification of headaches published by the [[International Headache Society]]. It contains explicit (operational) [[diagnostic criteria]] for headache disorders. The first version of the classification, ICHD-1, was published in 1988. The current revision, ICHD-2, was published in 2004.<ref>{{cite book |title=The Headaches |edition=3 |publisher=[[Lippincott Williams & Wilkins]] |year=2005  | vauthors = Olesen PJ, Goadsby NM, Ramadan P, Tfelt-Hansen KM, Welch |ref={{Harvid|Olesen et al.|2005}}}}</ref> The classification uses numeric codes. The top, one-digit diagnostic level includes 14 headache groups. The first four of these are classified as primary headaches, groups 5-12 as secondary headaches, [[Human cranium|cranial]] [[neuralgia]], central and primary facial pain and other headaches for the last two groups.<ref>{{cite book |title=Comprehensive Review of Headache Medicine |publisher=[[Oxford University Press]] |year=2008| isbn=978-0-19-536673-0 | vauthors = Levin M, Baskin SM, Bigal ME |ref={{Harvid|Levin et al.|2008}}}}</ref>

The ICHD-2 classification defines [[migraine]]s, tension-types headaches, cluster headache and other [[trigeminal]] autonomic headache as the main types of primary headaches.<ref name="IHS_ICHD2" /> Also, according to the same classification, stabbing headaches and headaches due to [[cough]], exertion and sexual activity ([[sexual headache]]) are classified as primary headaches. The daily-persistent headaches along with the hypnic headache and thunderclap headaches are considered primary headaches as well.<ref>{{cite book | vauthors = Linn FH | title = Headache | chapter = Primary thunderclap headache | volume = 97 | pages = 473–481 | date = 2010 | pmid = 20816448 | doi = 10.1016/s0072-9752(10)97042-5 | publisher = Elsevier | isbn = 978-0-444-52139-2 | series = Handbook of Clinical Neurology }}</ref><ref>{{cite journal | vauthors = Obermann M, Holle D | title = Hypnic headache | journal = Expert Review of Neurotherapeutics | volume = 10 | issue = 9 | pages = 1391–1397 | date = September 2010 | pmid = 20839413 | doi = 10.1586/ern.10.112 | s2cid = 19141493 }}</ref>

Secondary headaches are classified based on their cause and not on their [[symptoms]].<ref name="IHS_ICHD2" /> According to the ICHD-2 classification, the main types of secondary headaches include those that are due to head or neck trauma such as [[Whiplash (medicine)|whiplash injury]], [[intracranial hematoma]], post [[craniotomy]] or other head or neck injury. Headaches caused by cranial or cervical vascular disorders such as [[Stroke#Ischemic stroke|ischemic stroke]] and [[transient ischemic attack]], non-traumatic intracranial hemorrhage, [[Cerebral arteriovenous malformation|vascular malformations]] or [[arteritis]] are also defined as secondary headaches. This type of headache may also be caused by [[cerebral venous thrombosis]] or different intracranial vascular disorders. Other secondary headaches are those due to intracranial disorders that are not vascular such as low or high pressure of the cerebrospinal fluid pressure, non-infectious inflammatory disease, intracranial neoplasm, [[epileptic seizure]] or other types of disorders or diseases that are intracranial but that are not associated with the vasculature of the [[central nervous system]].{{citation needed|date=June 2021}}

ICHD-2 classifies headaches that are caused by the ingestion of a certain substance or by its withdrawal as secondary headaches as well. This type of headache may result from the overuse of some medications or exposure to some substances. [[HIV]]/[[AIDS]], intracranial [[infections]] and systemic infections may also cause secondary headaches. The ICHD-2 system of classification includes the headaches associated with homeostasis disorders in the category of secondary headaches. This means that headaches caused by [[Kidney dialysis|dialysis]], [[high blood pressure]], [[hypothyroidism]], cephalalgia and even [[fasting]] are considered secondary headaches. Secondary headaches, according to the same classification system, can also be due to the injury of any of the facial structures including [[teeth]], jaws, or [[temporomandibular joint]]. Headaches caused by psychiatric disorders such as [[somatization]] or [[psychotic disorders]] are also classified as secondary headaches.{{citation needed|date=June 2021}}

The ICHD-2 classification puts cranial neuralgias and other types of [[neuralgia]] in a different category. According to this system, there are 19 types of neuralgias and headaches due to different central causes of facial pain. Moreover, the ICHD-2 includes a category that contains all the headaches that cannot be classified.{{citation needed|date=June 2021}}

Although the ICHD-2 is the most complete headache classification there is and it includes frequency in the diagnostic criteria of some types of headaches (primarily primary headaches), it does not specifically code frequency or severity which are left at the discretion of the examiner.<ref name="IHS_ICHD2" />

==== NIH ====
{{Main|NIH classification of headaches}}
The NIH classification consists of brief definitions of a limited number of headaches.{{sfn|Levin et al.|2008|page=60}}

The NIH system of classification is more succinct and only describes five categories of headaches. In this case, primary headaches are those that do not show organic or structural causes. According to this classification, primary headaches can only be vascular, [[myogenic]], cervicogenic, traction, and inflammatory.<ref>{{Cite web|title=Headache Information Page {{!}} National Institute of Neurological Disorders and Stroke|url=https://www.ninds.nih.gov/Disorders/All-Disorders/Headache-Information-Page|access-date=21 July 2021|website=www.ninds.nih.gov}}</ref>