1.       Introduction

The 3rd edition of the International Classification of Headache Disorders (ICHD-3) can be very helpful to clinicians who manage patients presenting with headache as their chief complaint [1]. Unfortunately, however, many clinicians are still unaware of this important reference resource, which describes many headache diagnoses with significant overlap in presentation and sometimes subtle points of diagnostic differentiation. If all headaches classifications were best managed using the same treatments, precise identification of the headache types would be less important. However, because therapeutic management varies significantly depending on the specific type of headache, a more precise diagnosis can make a difference in treatment success [2]. Not only is headache a prevalent disorder worldwide in many practice settings, but it is also a particularly common emergency department chief complaint [2-5]. Consequently, by gaining maximal diagnostic competence of this condition, thus improving therapeutic accuracy, clinicians can have a positive impact on the lives of untold numbers of patients. Detailed delineations and diagnostic descriptions of specific headache types are provided in the International Classification of Headache Disorders (ICHD-3), which can be easily accessed online [1]. The goal of this paper, therefore, is not to restate these diagnostic criteria; but to increase awareness of this useful clinical resource, and present some of its higher yield information via simplified tables and an algorithm.

2.       ICHD-3 Classifications

The International Classification of Headache Disorders (ICHD-3) has been developed by an international panel of headache experts. It is now in its third edition and currently is published in a digital beta format, in order to enable input from other the members of the International Headache Society and allow a test period for identification and correction of mistakes [1]. Since the extensive document is nearly impossible to learn by heart, the International Classification of Headache Disorders (ICHD-3) is intended to be a reference tool which can be consulted time and time again.

This classification reference has three main sections. Part one covers primary headaches, part two covers secondary headaches, and part three covers painful cranial neuropathies, as well as other facial pains and headaches. The differentiation between primary and secondary headaches is relatively simple and easy to understand. A primary headache is due to the actual headache condition itself and cannot be attributed to another etiology; while a secondary headache is a symptom of another, underlying condition. Primary headaches include four general types-migraine, tension-type headache, trigeminal autonomic cephalalgias, and other primary headache disorders. Each of these four headache classifications are further sub-classified. The classification of secondary headaches is much more extensive, due to the vast array of underlying conditions which can produce a headache. Examples include headaches due to trauma or injury of the head and/or neck, headaches attributed to cranial or cervical vascular disorders, and headaches attributed to a substance or its withdrawal. These categories, too, are further divided into sub-categories [1]. These sub-classifications of all potential headache types can become quite challenging for the busiest clinicians to remember.

2.1.  Primary Headache Classifications

Primary headaches include the well-known (but still not well understood) migraine and tension-type headaches, as well as many lesser-known and -diagnosed headaches. Migraine headaches and their sub-classifications have specific diagnostic criteria which differentiate them from other headaches and craniofacial pains [1]. They are most effectively treated with antipsychotics and other antidopaminergic medications, which are usually administered alongside other analgesics and adjunct treatments, sometimes including diphenhydramine to reduce incidence of akathisia [4]. Tension-type headaches, which some consider to be part of a headache spectrum with migraines, also have specific diagnostic criteria and sub-classifications [5]. They respond to the same treatments used for migraine headaches, as well as over-the-counter medications including combinations formulations with caffeine⁶. The third section of primary headaches classification covers the trigeminal autonomic cephalalgias, which include cluster headaches, paroxysmal hemicrania, short-lasting unilateral neuralgiform headaches, hemicrania continua, and probable trigeminal autonomic cephalalgia; each of which have specific diagnostic criteria and distinct treatment recommendations¹. Without the benefit of the ICDH-3 classification system, the diagnosis and correct treatment of these conditions, all of which present with similar stabbing type pain and ipsilateral autonomic symptoms [1], would be almost impossible for clinicians not specialized in this particular area. The fourth category of primary headaches is for other primary headache disorders, and includes a number of less common headache conditions, including primary cough headache, primary exercise headache, primary headache associated with sexual activity, primary thunderclap headache, cold-stimulus headache, external-pressure headache, primary stabbing headache, nummular headache, hypnic headache and new daily persistent headache [1].

A helpful diagnostic algorithm for primary headaches (Algorithm 1), and a table including the primary headache classifications, current management, prophylaxis recommendations, and mimics (Table 1), are provided in this paper.

2.2.  Secondary Headache Classifications

A secondary headache is a headache which is present because of another medical condition, and generally carry a higher level of concern for clinicians because the underlying etiology is sometimes a life-threatening condition such as bacterial meningitis or intracranial hemorrhage [1]. The challenge associated with secondary headaches is in differentiating them from the more common, and less worrisome, primary headache etiologies which they frequently mimic. Failure to accurately diagnose a secondary headache will frequently have serious consequences and complications. See (Table 2) for the International Classification of Headache Disorders (ICHD-3) categories, and (Table 3) for a selection of these secondary headaches which may mimic more common primary headaches, as well as their emergent management.

2.3.  Painful Cranial Neuropathies, Other Facial Pains, and Other Headaches

A separate and third section in the International Classification of Headache Disorders (ICHD-3) is dedicated to the cranial neuropathies, other facial pains, and other headaches. Many, but not all of these conditions, are characterized by neuropathic-type pain in a specific cranial nerve distribution. These include trigeminal neuralgia, occipital neuralgia, optic neuritis and other, lesser-known neuropathies, as well as a section dedicated to headaches without a clear-cut etiology or not fitting specific diagnostic criteria for any other headache diagnosis. Again, the most current diagnostic criteria for each of these conditions, as determined by the ICHD-3 panel of experts, is provided for the clinician. See (Table 4) for a list of these conditions [1].

3.       Conclusion

In summary, the 3rd edition of the International Classification of Headache Disorders (ICHD-3) is an extremely valuable tool in the diagnosis and therapeutic management of the complex spectrum of head and face pain syndromes [1]. Because therapeutic success is most likely to occur when the type or cause of the headache or face pain is correctly identified, a precise diagnosis is critical [2].

Algorithm 1: Diagnosis of Primary Headaches.

Table 1: Primary headaches, management, prophylaxis, and mimics..

Table 2: Secondary headache classifications.

Table 3: Selected secondary headaches which mimic primary headaches, and their emergent management Painful cranial neuropathies, other facial pains, and other headaches.

Table 4: Painful cranial neuropathies and other facial pains.

1. Headache Classification Committee of the International Headache Society (2013) The International Classification of Headache Disorders, 3rd edition (beta version). Cephalalgia. 33: 629-808.
2. Cerbo R, Villani V, Bruit G, Di Stani F, Mostardini C (2005) Primary headache in Emergency Department: prevalence, clinical features and therapeutical approach. J Headache Pain 6: 287-289.
3. Stovner L, Hagen K, Jensen R, Katsarava Z, Lipton R, et al. (2007) The global burden of headache: a documentation of headache prevalence and disability worldwide. Cephalalgia 27: 193-210.
4. Sumamo Schellenberg E, Dryden DM, Pasichnyk D, Ha C, Vandermeer B, et al. (2012) Acute Migraine Treatment in Emergency Settings [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US). (Comparative Effectiveness Reviews, 84).