Keywords

1 Introduction

Headache is common—one of the most frequently experienced symptoms of mankind [1]. Almost everybody has experience of it. It is also one of the most common medical complaints, which is not the same thing. To put some numbers to these statements, at least 40% of adults in all countries report headache as a recurring nuisance, 10–30% are at least sometimes disabled by it and 2–10% bear it, with varying levels of incapacity, on more days than not [2, 3].

This very attribute somehow, perversely, works against it. Headache is so common that people often regard it as “normal”, a perception that fosters a marked societal ambivalence towards it: while it renders some people almost helpless, others look upon all manifestations of headache with scorn or derision. Headache is the most frequent cause of consultation in both primary care and neurological practice [3]. It prompts many visits to internists, ENT specialists (otorhinolaryngologists), ophthalmologists, dentists, orthopaedic surgeons, psychologists and the proponents of a wide variety of complementary and alternative medical practices [3]. Headache is far from unknown as a presenting symptom in emergency departments, although it rarely signals serious underlying illness.

Headache may be mostly benign, but it hurts, and with pain comes disability. When headache is recurrent, repeated episodes of disability diminish quality of life, while impaired productivity leads to financial loss—each a personal burden. The public-health and societal importance of headache lies in these causal associations expressed in large numbers of people.

2 Headache Disorders

Headache itself is a feature, often characteristic, of a very large number of disorders. The International Classification of Headache Disorders (ICHD) describes more than 200 headache types, subtypes or subforms [1]. As Table 2.1 shows, ICHD distinguishes between primary headaches, which have no other underlying causative disorder, and secondary headaches, attributed to some other disorder. The third section of ICHD covers painful cranial neuropathies and other facial pain [1].

Table 2.1 International classification of headache disorders, 3rd edition (ICHD-3) [1]
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Tables 2.2, 2.3 and 2.4 briefly describe the relatively few of these disorders that are common or, for other reasons, important. These are the headaches of which all healthcare providers, including and especially those in primary care, should have knowledge and some understanding in order to meet the very substantial need they generate for professional care. The secondary headaches in Table 2.3 must never be missed. As for the primary headaches (Table 2.2), effective management of these is often achievable without recourse to professional care, by lifestyle adaptation and appropriate use of over-the-counter (OTC) medications. But equally often this is not the case, and the need for professional care arising from these disorders places a substantial demand on health services. Recognition of where this demand comes from, and an understanding based on empirical evidence of the people and the disorders that most contribute to it, are key to the design and implementation of headache services, and to the delivery, within these, of effective, efficient and equitable headache care.

Table 2.2 Important primary headaches in ICHD-3 [1]
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Table 2.3 Important secondary headaches in ICHD-3 [1]
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Table 2.4 Important painful cranial neuropathies and other facial pain in ICHD-3 [1]
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Two primary headache disorders—migraine and tension-type headache (TTH)—are widespread, prevalent and often lifelong conditions. These are subjects of this monograph; secondary headache disorders, with the single exception of medication-overuse headache (MOH), are not—even those listed in Table 2.3. Collectively, migraine, TTH and MOH affect at least 40% of most populations [4] and are the cause of much disability throughout the world [4, 5]. Other headache disorders, such as cluster headache, may be highly disabling at individual level, but they are too uncommon to signify at societal level.Footnote 1

2.1 Migraine

At the societal level, migraine far outweighs all other headache disorders in its deleterious effect on health. It is second only to low back pain among all causes of disability [4, 5], responsible for almost half the financial cost of headache [6], and the principal progenitor of MOH, which is responsible for another third [6].

Migraine is the most recognized and best studied of the headache disorders [1]. It is a familial disorder, with a genetic component not yet fully understood. Its prevalence among adults varies worldwide, from 9.3% in China [7] to over 30% in Nepal [8] according to studies conducted with similar methods, and therefore comparable [9, 10]. The global mean is almost certainly higher than the current estimate of about 15% [5, 6]. The Global Burden of Disease study 2010 (GBD2010) ranked migraine as the third most prevalent disorder in the world [11]. Women are 1.5–3 times more likely to be affected than men [2] because of hormonal influences [1].

Migraine is an unpleasant illness. In the great majority of cases, it is a recurrent episodic disorder starting in childhood or adolescence (in girls, in particular, it may start at puberty) and in many cases lasting throughout life. Attack frequency is subject to lifestyle and environmental factors and varies widely between and within individuals, averaging once or twice a month. Headache and nausea (with or without vomiting) are the most characteristic attack features; photophobia and phonophobia are common and relatively specific symptoms [1]. The headache, lasting for hours to 2–3 days, is typically moderate or severe and likely to be unilateral, pulsating and aggravated by routine physical activity [1].

Migraine has two major types. Migraine without aura is a clinical syndrome characterized by these features, most of which are captured in the diagnostic criteria of ICHD [1] (Table 2.5). About 10% of migraine attacks overall are migraine with aura, experienced only by a third of people with migraine and distinguished by the transient focal neurological symptoms that usually precede but sometimes accompany the headache [1] (Table 2.5). Some people, with either type of migraine, also experience a prodromal phase, occurring hours or days before the headache, and/or a postdromal phase following headache resolution. Common prodromal symptoms include fatigue, elated or depressed mood, unusual hunger and cravings for certain foods; postdromal symptoms include fatigue, elated or depressed mood and cognitive difficulties. Together, this array of symptoms, not surprisingly, are disabling: GBD2016 [4] and GBD2017 [5] ranked migraine as the second-highest cause of disability worldwide.

Table 2.5 ICHD-3 diagnostic criteria for migraine with and without aura [1]
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Between attacks, most people with either of these migraine types are completely well. However, for many, attacks tend to be unpredictable: they can start at any time, and some people are more prone to attacks than are others. So-called trigger factors play a part in this. While this calls for their avoidance as a sensible management tactic, avoidance itself, involving lifestyle compromise, can be a factor relevant to burden (Chap. 4).

A third type, chronic migraine, is specifically characterized by very frequent attacks and/or loss of episodicity. Headache occurs on 15 or more days per month, but not always with the features of migraine headache (for the diagnosis, these are required only on 8 or more days per month [1]). Chronic migraine is very highly disabling, but it still lacks a universally accepted definition. The criteria of ICHD-3 [1] (Table 2.6) may appear to be authoritative but are regularly modified by researchers and authors, so that the disorder is confusingly conflated with MOH (e.g., [12, 13]). Therefore, the prevalence of chronic migraine has not been reliably established. By the best working definition, it is rare [14], and, like cluster headache, not itself of great public-health importance.Footnote 2

Table 2.6 ICHD-3 diagnostic criteria for chronic migraine [1]
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2.2 Tension-Type Headache (TTH)

TTH is the most prevalent of all the headache disorders, but highly variable in its expression and uncommonly a cause of serious disability. It has some societal importance, but much less than that of migraine.

TTH is the common sort of headache that nearly everyone has occasionally, so that many people refer to it as “normal” or “ordinary” headache, terms that deny its status as a headache disorder. While GBD2010 ranked it as the second most prevalent disorder in the world (behind dental caries) [10], its reported prevalence is nonetheless hugely variable [2]. This, probably, is due in most part to under-reporting of mild cases. The true prevalence probably exceeds 50% [2], but only when infrequent episodic TTH is included (less than 1 episode per month), which may indeed fall outside the definition of headache disorder [1]. In most but not all populations, TTH affects rather more women than men; children report it also, but to a lesser extent.

TTH episodes vary greatly in duration, from minutes to several days, but usually last a few hours. Their frequency also varies widely, both between people and in individual people over time. The pain of TTH lacks the specific characteristics of migraine, as is reflected in the diagnostic criteria of ICHD [1] (Table 2.7): it neither worsens with routine physical activity nor is associated with nausea (although either photophobia or phonophobia may be present). Further, it is usually bilateral or generalized; people describe it as a squeezing or pressure, like a tight band around the head—the opposites of descriptions of migraine headache. TTH often spreads down to or up from the neck. Although mostly moderate or mild, this headache can be bad enough to make it difficult to carry on entirely as normal [15].

Table 2.7 ICHD-3 diagnostic criteria for the important types of tension-type headache [1]
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TTH pursues a highly variable course, commonly beginning in the teenage years and reaching peak levels in the 30s. Although never serious, in a few people TTH becomes bothersome enough to need medical attention, usually because it has become frequent. There are distinct types although, in any individual, one may give way to another. Two are important (Table 2.7). Frequent episodic TTH occurs, like migraine, in attack-like episodes. Chronic TTH, which has a prevalence of up to 3% in adults [2], is a disorder evolving from frequent episodic TTH, with daily or very frequent episodes of similarly described headache, lasting hours to days and sometimes unremitting over long periods. This headache may be associated with mild nausea [1]. It can be quite disabling and distressing.

2.3 Medication-Overuse Headache (MOH)

MOH may top the list in terms of societal importance, not because it is the most prevalent headache disorder but for two other reasons: at individual level it is the most disabling and by far the most costly of the common headaches [6], and, unlike migraine and TTH, it is wholly avoidable.

ICHD defines MOH as a secondary headache [1], but it occurs only in patients with a prior headache disorder. The cause is chronic excessive use of medication(s) taken to treat that headache. MOH is therefore better considered as a sequela of a primary headache disorder, more usually migraine than TTH. This was recognized in GBD2016 [4], and again in GBD2017 [5], which, instead of reporting MOH separately, attributed its disability burden proportionately to these primary headaches (see Chap. 9).

All medications used to treat acute headache are associated with this problem, although the mechanism through which MOH develops undoubtedly varies between different drug classes. Wherever they are available, opioids such as codeine tend especially to be implicated, but this probably is a consequence of selection by patients who erroneously believe the solution lies in “stronger” medications, coupled with the exhortative messages by which codeine-containing medications are generally promoted to the public (Fig. 2.1). The risk of MOH escalates with medication frequency regardless of the drug, and is high whenever these treatments are taken regularly on more than 2–3 days a week. In individual patients, an evolutionary course can often be retrospectively charted: the usual start is that occasional headache attacks increase in frequency, through natural variation or because an additional headache has developed. Medication use follows, also becoming more frequent, and this is encouraged initially by its apparent efficacy. Over time, weeks or sometimes very much longer, as headache episodes and medication intake become ever more frequent, efficacy wanes. Natural responses then are to switch to medications perceived to be stronger, and to increase doses. While these behaviours lead inexorably to worsening in the long term, attempts at withdrawal induce immediate—and highly discouraging—aggravation of symptoms. In the end-stage, if this process is not interrupted, MOH is unremitting, only fluctuating with medication use repeated every few hours.

Fig. 2.1
figure 1

Promotional message, aimed at the public and typical of many, for a branded over-the-counter codeine-containing acute migraine therapy

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Correct diagnosis is important for these reasons, and more so because patients will not improve without withdrawal of the offending medication(s), which are often multiple. On the other hand, most patients with MOH improve within 2 months after withdrawal, as does their responsiveness to preventative treatment.

The ICHD diagnostic criteria [1] for MOH are in Table 2.8. It is an oppressive headache, obviously persistent, and highly disabling.

Table 2.8 ICHD-3 diagnostic criteria for medication-overuse headache [1]
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MOH has a highly variable prevalence worldwide, and estimates are uncertain [16]; while the average is 1.5–2% in adults [17], some national estimates exceed 7% with reasonable certainty [18, 19]. Factors contributing are high prevalences of the progenitor headaches (putting more people at risk) and, probably, easy access to OTC medications coupled with poor access to healthcare and lack of public health-education [18, 19].

3 Concluding Remarks

Although more than 200 headache disorders are clearly defined by their distinct characteristics and clinical features [1], and several of these disorders are described here, just three contribute significantly to the societal impact of headache. Migraine, TTH and MOH overwhelm all others in their shares of the total population ill health that is attributable to headache. Furthermore, MOH may properly be regarded as a sequela of migraine and TTH; its burdens in reality belong to these two primary headache disorders [4, 5].

It is essentially for these few conditions that society must make provision, if it wishes to lessen the impact. This fact makes the task (described in Chap. 15) a great deal easier.