Lipton, R B. MD; Bigal, M E. MD, PhD; Steiner, T J. MB, PhD, LLM; Silberstein, S D. MD; Olesen, J MD, PhD
Given the range of disorders that produce headache, a systematic approach to classification and diagnosis is an essential prelude to clinical management. For the last 15 years, the diagnostic criteria of the International Headache Society (IHS) have been the accepted standard. The second edition of The International Classification of Headache Disorders (January 2004) reflects our improved understanding of some disorders and the identification of new disorders. Neurologists who treat headache should become familiar with the revised criteria. Like its predecessor, the second edition of the IHS classification separates headache into primary and secondary disorders. The four categories of primary headaches include migraine, tension-type headache, cluster headache and other trigeminal autonomic cephalalgias, and other primary headaches. There are eight categories of secondary headache. Important changes in the second edition include a restructuring of these criteria for migraine, a new subclassification of tension-type headache, introduction of the concept of trigeminal autonomic cephalalgias, and addition of previously unclassified primary headaches. Several disorders were eliminated or reclassified. In this article, the authors present an overview of the revised IHS classification, highlighting the primary headache disorders and their diagnostic criteria. They conclude by presenting an approach to headache diagnosis based upon these criteria.
Headache is one of the most common reasons for neurologic consultation.1,2 Given the range of disorders that present with headache, a systematic approach to headache classification and diagnosis is essential both to good clinical management and to useful research. For the last 15 years, the 1988 classification of the International Headache Society (IHS)3 has been the accepted standard for headache diagnosis, establishing both uniform terminology and consistent operational diagnostic criteria for the entire range of headache disorders. Translation into 22 languages has facilitated clinical practice, epidemiologic studies, and multinational clinical trials. The criteria provide the basis for clinical trials guidelines for several conditions.4 With the publication of the second edition of The International Classification of Headache Disorders (ICHD-2)5 in January 2004, neurologists who treat headache should become familiar with the revised criteria, which will become the standard for treatment and research. Although the basic structure and most of the original categories are preserved, there were many changes that will influence neurologic practice. These changes include a restructuring of the criteria for migraine, new subclassification of tension-type headache (TTH), introduction of the concept of trigeminal autonomic cephalalgias (TACs), and addition of several previously unclassified types of primary headache. The revised classification was developed by a panel of experts in the field chosen by the IHS. Although we attempted to review the relevant literature, the classification represents a clinical consensus based on data, experience, judgment, and compromise. Nonetheless, the classification provides a foundation for clinical practice and research, and will eventually itself be revised.
In this article we present an overview of the ICHD-2,5 highlighting the primary headache disorders and their diagnostic criteria. We then offer an algorithmic approach to primary headache diagnosis based on attack frequency and duration, using the ICHD-2.
Like the 1988 classification, The International Classification of Headache Disorders, 2nd edition, groups headache disorders into primary and secondary headaches. The four categories of primary headache include migraine, TTH, cluster headache (CH) and other TACs, and other primary headaches. There are also eight categories of secondary headache (table 1), and a third group that includes central and primary causes of facial pain and other headaches. The criteria for the primary headaches are clinical and descriptive and, with a few exceptions (i.e., familial hemiplegic migraine [FHM]), are based on headache features, not etiology. In contrast, secondary headaches are attributed to another underlying disorder.
|Table 1 First level of The International Classification of Headache Disorders, 2nd edition|
Key operational rules for the classification are summarized below.5
Migraine is classified into five major categories, the two most important of which are migraine without aura (1.1) and migraine with aura (1.2). The diagnostic criteria for migraine without aura are unchanged from 1988. However, there is a restructuring of the criteria for migraine with aura. Chronic migraine (1.5.1) has been added. Ophthalmoplegic migraine, now considered a cranial neuralgia, has been moved to item 13 (cranial neuralgias and central causes of facial pain). When a patient fulfills criteria for more than one type of migraine, each type should be diagnosed and coded. Since chronic migraine usually develops from episodic migraine, a patient coded 1.5.1 will usually have an additional code for the antecedent disorder (usually 1.1).
Relative to those of 1988, the diagnostic criteria for migraine without aura (1.1) are little modified (table 2). They require at least five lifetime attacks, lasting 4 to 72 hours, with at least two of four pain features and at least one of two sets of associated symptoms. In children, attacks may be shorter, 1 to 72 hours, and in young children photophobia and phonophobia may be inferred from behavior rather than reported. In addition, when attacks occur on >=15 days/month, the diagnoses are chronic migraine (1.5.1) plus migraine without aura (1.1).
|Table 2 ICHD-2 diagnostic criteria for 1.1 Migraine without aura|
As before, criteria for migraine without aura are met by various combinations of features. With regard to pain, unilateral, pulsating headache meets the criteria but so does bilateral, pressing headache if it is moderate or severe in intensity and aggravated by routine physical activity. With regard to associated features, a patient without nausea or vomiting but with both photophobia and phonophobia may fulfill the criteria (see table 2).
The criteria for migraine with aura (1.2) have been revised substantially. The typical aura of migraine is characterized by focal neurologic features that usually precede migrainous headache but may accompany it or occur in the absence of the headache (table 3).6 Typical aura symptoms develop over >=5 minutes and last no more than 60 minutes, and visual aura is overwhelmingly the most common.7 Typical visual aura is homonymous, often having a hemianopic distribution and expanding in the shape of a crescent with a bright, ragged edge, which scintillates. Scotoma, photopsia, or phosphenes and other visual manifestations may occur. Visual distortions such as metamorphopsia, micropsia, and macropsia are more common in children.8-10
|Table 3 ICHD-2 criteria for 1.2.1 Typical aura with migraine headache|
Sensory symptoms occur in about one-third of patients who have migraine with aura.11 Typical sensory aura consists of numbness (negative symptom) and tingling or paresthesia (positive symptoms). The distribution is often cheiro-oral (face and hand). Dysphasia may be part of typical aura but motor weakness, symptoms of brainstem dysfunction, and changes in level of consciousness, all of which may occur,12 signal particular subtypes of migraine with aura (hemiplegic, and basilar-type).
Recently, typical migraine aura has been noted to occur with non-migrainous headache (i.e., headache not fulfilling the criteria of 1.1). Such cases are coded typical aura with non-migraine headache (1.2.2). Reports have associated apparently typical aura with CH, chronic paroxysmal hemicrania, and hemicrania continua (HC).1315 These cases are classified according to both disorders [e.g., CH (3.1) plus typical aura with non-migraine headache (1.2.2)].
Typical aura occurring in the absence of any headache 1618 is coded typical aura without headache (1.2.3), a disorder most often reported by middle-aged men.24 Differentiating this benign disorder from TIA, a medical emergency, may require investigation, especially when it first occurs after age 40, when negative features (i.e., hemianopia) are predominant, or when the aura is of atypical duration.19
FHM (1.2.4) is the first migraine syndrome to be linked to a specific set of genetic polymorphisms.2023 The criteria for this disorder 9 include those of migraine with aura (1.2) except that aura includes some degree of motor weakness (hemiparesis) and may be more prolonged than 60 minutes (up to 24 hours); additionally, at least one first-degree relative has had similar attacks (also meeting these criteria). Cerebellar ataxia may occur in 20% of FHM sufferers. The onset of weakness may be abrupt, but usually lasts less than 1 hour.24 A person with FHM may develop migraine with aura on adulthood and migraine without aura later in life.24
The two known loci for FHM are on chromosomes 1 and 19, but some families do not link to either of these, indicating that there is at least one additional locus.25,26
Patients otherwise meeting these criteria but who have no family history of this disorder are classified as sporadic hemiplegic migraine (1.2.5), a disorder new to the revised classification.27
Basilar-type migraine (1.2.6) is a new term, replacing basilar migraine. The change is intended to remove the implication that the basilar artery (or, necessarily, its territory) is involved. The distinguishing feature of basilar-type migraine is a symptom profile that suggests posterior fossa involvement.28 Diagnosis requires at least two of the following aura symptoms, all fully reversible: dysarthria, vertigo, tinnitus, decreased hearing, double vision, visual symptoms simultaneously in both temporal and nasal fields of both eyes, ataxia, decreased level of consciousness, and simultaneously bilateral paresthesias. Because 60% of patients with FHM have basilar-type symptoms, basilar-type migraine should be diagnosed only when weakness is absent. The headache meets criteria for 1.1 migraine without aura (see table 2).
A number of more or less well-described disorders are classified under this heading.29
Cyclical vomiting (1.3.1) occurs in up to 2.5% of schoolchildren.3032 The hallmark of this disorder is recurrent and stereotyped episodes of intense but otherwise unexplained nausea and vomiting which last 1 hour to 5 days in children free of symptoms interictally. Vomiting occurs at least four times in an hour, and no signs of gastrointestinal disease can be found.
Abdominal migraine (1.3.2) afflicts up to 12% of schoolchildren with recurrent attacks of abdominal pain associated with anorexia, nausea, and sometimes vomiting.33,34 The abdominal pain has all of the following characteristics: midline location, periumbilical or poorly localized; dull or just sore quality; moderate or severe intensity. During it, there are at least two of anorexia, nausea, vomiting, and/or pallor. Physical examination and investigations exclude other causes of these symptoms.
Benign paroxysmal vertigo (1.3.3) is a disorder characterized by recurrent (at least five) attacks, each of multiple episodes of severe vertigo resolving spontaneously after minutes to hours.35 Neurologic examination and audiometric and vestibular functions are all normal between attacks, and the EEG is also normal.
This disorder is rare. Recurrent attacks (at least two) of fully reversible scintillations, scotomata, or blindness, affecting one eye only, are accompanied or followed within 1 hour by migrainous headache (fulfilling criteria for 1.1). Other causes of monocular visual loss, including TIA, optic neuropathy, and retinal detachment, must be ruled out by appropriate investigation.36 A recent review suggests that many patients with monocular aura experience retinal infarction of migrainous origin.37 These patients should be coded as migrainous infarction (1.5.4).
The ICHD-2 classifies chronic migraine (1.5.1) (see Controversies in the classification of chronic daily headache, below) when headache is both present and meets criteria for migraine on >=15 days per month for >=3 months, in the absence of medication overuse. Most cases of chronic migraine, following this approach, evolve from episodic migraine, and most from migraine without aura,38 hence its classification as a complication of migraine. When medication overuse is present 39 (acute anti-migraine drugs and/or opioids or combination analgesics taken on >=10 days/month, or simple analgesics on >=15 days/month), it is a likely cause of chronic headache. According to the ICHD-2, neither chronic migraine (1.5.1) nor medication-overuse headache (8.2) can be diagnosed with confidence until the overused medication has been withdrawn: improvement within 2 months is expected if the latter diagnosis is correct (and is necessary to confirm it), not if the former is present. Meanwhile, the codes to be assigned are that of the antecedent migraine (usually migraine without aura, 1.1) plus probable medication-overuse headache (8.2.7) plus probable chronic migraine (1.6.5).
Status migrainosus (1.5.2) refers to an attack of migraine with a headache phase lasting >72 hours.40 The pain is severe (a diagnostic criterion) and debilitating. Non-debilitating attacks lasting >72 hours are coded as probable migraine without aura (1.6.1).
Persistent aura without infarction (1.5.13) is diagnosed when aura symptoms, otherwise typical of past attacks, persist for >1 week. Investigation shows no evidence of infarction. It is an unusual but well-documented complication of migraine that is now being introduced into the IHS classification.40 If aura symptoms last more than 1 hour (typical aura), but less than 1 week (persistent aura without infarction), a code of 1.6.2 (probable migraine with aura), specifying the atypical feature (prolonged aura), should be assigned.
Migrainous infarction (1.5.4) is an uncommon occurrence. One or more otherwise typical aura symptoms persist beyond 1 hour and neuroimaging confirms ischemic infarction. Strictly applied, these criteria distinguish this disorder from other causes of stroke, which must be excluded 41: the neurologic deficit develops during the course of an apparently typical attack of migraine with aura, and exactly mimics the aura of previous attacks.
Migraine and epilepsy are comorbid disorders.42 Headaches are common in the postictal period, but epilepsy can be triggered by migraine (migralepsy). The criteria for migraine-triggered seizure (1.5.5) require that a seizure fulfilling diagnostic criteria for one type of epileptic attack occurs during or within 1 hour after a migraine aura.
Between 10% and 45% of patients with features of migraine fail to meet all criteria for migraine (or any of its subtypes).42 If a single criterion is missing (and the full set of criteria for another disorder are not met), the applicable code is probable migraine (1.6). Epidemiologic studies demonstrate that probable migraine is common and associated with temporary disability and reduction in health-related quality of life.43
TTH is the most common type of primary headache, with 1-year period prevalences ranging from 31 to 74%.44 The 1988 classification distinguished two subtypes, ETTH (<15 attacks per month) and chronic TTH (CTTH) (>=15 attacks per month).3 The revised classification distinguishes three subtypes: infrequent ETTH (2.1) (headache episodes on <1 day per month), frequent ETTH (2.2) (headache episodes on 1 to 14 days per month), and CTTH (2.3) (headache on >=15 days per month, perhaps without recognizable episodes).9
The diagnostic criteria for TTH are presented in table 4. In contrast to migraine, the main pain features of TTH are bilateral location, non-pulsating quality, mild to moderate intensity, and lack of aggravation by routine physical activity. The pain is not accompanied by nausea, although just one of photo- or phonophobia does not exclude the diagnosis.
|Table 4 ICHD-2 criteria for episodic tension-type headache (TTH)|
CTTH evolves from ETTH in most cases. This feature of evolution is described in the notes but is not part of the formal criteria. Like chronic migraine, CTTH cannot be diagnosed in patients overusing acute medication (see Controversies in the classification of chronic daily headache, below). Such patients often meet criteria for, and in fact have, medication-overuse headache (8.2), although withdrawal of the medication is required to confirm this diagnosis. A recently recognized disorder that phenotypically resembles CTTH, but is nosologically distinct from it (as far as is known), does not evolve from an episodic headache but is daily and unremitting from onset or within 3 days of onset. This condition is separately classified as new daily-persistent headache (4.8).
This code is used when headache fulfills all but one of the criteria for TTH and does not fulfill criteria for migraine without aura.
The addition of the term TACs to the classification reflects the observation that CH is one of a group of primary headache disorders characterized by trigeminal activation coupled with parasympathetic activation.45 The revised classification includes several disorders not quoted in the previous edition.
The diagnostic criteria for CH have not substantially changed. This disorder manifests as intermittent, short-lasting, excruciating unilateral head pain accompanied by autonomic dysfunction. The pain of CH is described variously as sharp, boring, drilling, knife-like, piercing, or stabbing, in contrast to the pulsating pain of migraine. It usually peaks in 10 to 15 minutes but remains excruciatingly intense for an average of 1 hour within a duration range of 15 to 180 minutes. During this pain, patients find it difficult to lie still, exhibiting often marked agitation and restlessness, and autonomic signs are usually obvious. After an attack, the patient remains exhausted for some time.46
CH is classified into two subtypes. Attacks of episodic CH (3.1.1) occur in cluster periods lasting from 7 days to 1 year separated by attack-free intervals of 1 month or more. Approximately 85% of CH patients have the episodic subtype. In chronic CH (3.1.2), attacks recur for >1 year without remission, or with remissions lasting <1 month. Chronic CH can evolve from episodic CH, or develop de novo,46 and may revert to episodic CH.
Patients have been described who have both CH and trigeminal neuralgia, and received the denomination of cluster-tic syndrome.45 In the IHS scheme they should receive both diagnoses.
As a group, the paroxysmal hemicranias have three main features: at least 20 frequent (more than five per day) attacks of short-lasting (2 to 30 minutes), severe and strictly unilateral orbital, supraorbital, or temporal pain; symptoms of parasympathetic activation ipsilateral to the pain (as in CH); absolute response to therapeutic doses of indomethacin.47,48
The 1988 classification included chronic paroxysmal hemicrania only. The revised classification includes episodic paroxysmal hemicrania (3.2.1) and chronic paroxysmal hemicrania (CPH) (3.2.2). Like CH, these disorders are distinguished by the presence or absence of attack-free intervals lasting 1 month or more.
Some patients with both CPH and trigeminal neuralgia have been described (CPH-tic syndrome)49; they should receive both diagnoses.
Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) syndrome (3.3) is a very rare primary headache. The diagnostic criteria require at least 20 high-frequency attacks (3 to 200 per day) of unilateral orbital, supraorbital, or temporal stabbing or pulsating pain, lasting 5 to 240 seconds and accompanied by ipsilateral conjunctival injection and lacrimation. The attacks are characteristically dramatic, with moderately severe pain peaking in intensity within 3 seconds and prominent tearing.50,51
Headache attacks believed to be a subtype of TAC but fulfilling all but one of the diagnostic criteria for it are diagnosed as probable TAC.
This group of miscellaneous primary headache disorders includes some mimics of potentially serious secondary headaches, which need to be carefully evaluated by imaging or other appropriate tests. Some, like hypnic headache, primary thunderclap headache, HC, and new daily-persistent headache were not included in the first IHS classification.
Episodic localized stabs of head pain occurring spontaneously in the absence of any structural cause (formerly referred to as jabs and jolts) are diagnosed as primary stabbing headache (4.1). Pain is exclusively or predominantly in the distribution of the first division of the trigeminal nerve (orbit, temple, and parietal area). It lasts for up to a few seconds and recurs at irregular intervals with a frequency ranging from one to many per day. Other features such as autonomic signs are lacking.52,53
This headache is brought on suddenly by coughing, straining, or Valsalva maneuver, and not otherwise, in the absence of any underlying disorder such as cerebral aneurysm or, especially, Arnold-Chiari malformation.54 Diagnostic neuroimaging, with special attention to the posterior fossa and base of the skull, is mandatory to differentiate secondary and primary forms of cough headache.55
This disorder is triggered by physical exercise, and not otherwise, and is distinguished from primary cough headache (4.2) (above) and headache associated with sexual activity (4.4) (below). Primary exertional headache is pulsating and lasts from 5 minutes to 48 hours. After the first occurrence of any exertional headache of sudden onset, appropriate investigations must exclude subarachnoid hemorrhage and arterial dissection.56
Headache precipitated by sexual activity usually begins as a dull bilateral ache as sexual excitement increases, and suddenly becomes intense at orgasm.57 Two subtypes are classified: pre-orgasmic headache (4.4.1), a dull ache in the head and neck, and orgasmic headache (4.4.2), explosive and severe and occurring with orgasm. Diagnosis of the latter requires exclusion of subarachnoid hemorrhage and arterial dissection.58
This primary headache disorder of the elderly 59 is characterized by short-lived attacks (typically 30 minutes) of nocturnal head pain that awaken the patient at a constant time each night, in many cases on more nights than not. It does not occur outside sleep. Hypnic headache is usually bilateral (although unilaterality does not exclude the diagnosis 60) and usually mild to moderate, very different from the unilateral orbital or periorbital knife-like intense pain of CH. Autonomic features are absent.
Severe headache of abrupt onset, which mimics the pain of a ruptured cerebral aneurysm, is classified as primary thunderclap headache (4.6), although this code is not applied to thunderclap headache meeting the criteria for 4.2, 4.3, or 4.4 (above). Intensity peaks in less than 1 minute. Pain lasts from 1 hour to 10 days and may recur within the first week after onset but not regularly over subsequent weeks or months.61 This diagnosis can be established only after excluding subarachnoid hemorrhage.
This daily and continuous strictly unilateral headache is defined by its absolute response to therapeutic doses of indomethacin. Pain is moderate, with exacerbations of severe pain, and autonomic symptoms accompany these exacerbations although less prominently than in CH and CPH.62,63 Some bilateral or alternating-side cases have been reported.64
The essence of this headache, which otherwise resembles CTTH (2.3), is that it is daily and unremitting from or very soon (<3 days) after onset. There is no history of evolution from episodic headache.38 If a history of progression from ETTH is present, a diagnosis of CTTH should be assigned. Diagnosis is not confirmed until it has been present for >3 months, and cannot be made if this manner of onset is not clearly recalled by the patient. Nor can it be made in the presence of medication overuse. New daily-persistent headache (NDPH) is typically bilateral, pressing or tightening in quality, of mild to moderate intensity, and unaffected by routine physical activity, although the diagnostic criteria require only any two of these features. There may be any but not more than one of photophobia, phonophobia, or mild nausea.
Chronic daily headache (CDH) of long duration is a clinical syndrome not included in the ICHD-2, defined by headaches that occur for >=4 hours a day on >=15 days a month over >3 months.37 CDH is one of the more common headache presentations to headache specialty care centers 65 and afflicts 4 to 5% of the general population.66 Several studies have reported difficulties using the 1988 system to classify CDH sufferers.67 As a consequence, several separate proposals for their classification have emerged.68 The Silberstein and Lipton (S-L) criteria have been most widely used.37
The S-L criteria divide primary CDH into transformed migraine (TM), CTTH, NDPH, and HC, and subclassify each of these into subtypes with medication overuse or without medication overuse. Of these, the 1988 classification included only CTTH while the revised classification has detailed diagnostic criteria for all four types of primary CDH of long duration.
The terms TM and chronic migraine (CM) have been used synonymously in the past but this is no longer appropriate: CM has a specific definition in the ICHD-2, which does not recognize TM as a separate entity. Three main differences exist between the IHS and S-L systems. First, the IHS criteria for CM require that headaches meeting criteria for migraine without aura (1.1) occur on >=15 days a month. To classify TM, the S-L criteria require only one of three links with migraine: a prior history of migraine meeting 1988 IHS criteria; a period of escalating headache frequency; concurrent and superimposed attacks of migraine that fulfill the IHS criteria. Second, IHS reserves the diagnosis of CM (1.5.1) from patients overusing acute medications (simple analgesics on >=15 days a month or ergotamine, triptans, opioids, or combination analgesics on >=10 days a month), applying instead probable chronic migraine (1.6.5) plus probable medication-overuse headache (8.2.7), and coding of the antecedent episodic migraine. The different approach of the S-L system adds with medication overuse to the diagnosis and defines the amounts of medication taken. Third, headache with migrainous features cannot be classified as NDPH according to the IHS criteria while the S-L classification allows this diagnosis in patients with headache features of migraine or ETTH if the disorder arises abruptly.
Headache diagnosis using the ICHD-2 should proceed in an orderly fashion. In this discussion, we assume one headache disorder is present. If multiple headache disorders occur together the conceptual process needs to be repeated for each.
First, one needs to distinguish primary from secondary headaches. The approach is to spot red flags that suggest the possibility of secondary headache (figure 1), to conduct the workup indicated by those red flags (table 5), and thereby to diagnose any secondary headache disorder that is present.69
|Figure 1. Algorithm for headache diagnosis (modified from reference 69).|
|Table 5 Red flags in the diagnosis of headache (modified from reference 69)|
In the absence of secondary headache, the clinician proceeds to diagnosing a primary headache disorder. If headache is atypical or difficult to classify, the possibility of secondary headache should be reconsidered, although the modifying effect of any treatment being taken should be kept in mind. We propose the approach to differential diagnosis based on figure 2.
|Figure 2. Algorithm for primary headache diagnosis. ETTH = episodic tension-type headache; CCH = chronic cluster headache; ECH = episodic cluster headache; CPH = chronic paroxysmal hemicrania; EPH = episodic paroxysmal hemicrania; CM = chronic migraine; CTTH = chronic tension-type headache; NDPH = new daily persistent headache; HC = hemicrania continua.|
The first step is to divide primary headache based on average monthly frequency of the headaches, into those of low-to-moderate frequency (<15 headache days per month), or those of high frequency (>=15 headache days per month). Second, based on average duration, classify the headache as shorter-duration (<4 hours a day) or longer-duration (>=4 hours). Low-to-moderate frequency headaches of long duration include migraine and ETTH; high frequency headaches of long duration include CM, CTTH, NDPH, and HC.
Third, for shorter-duration headache of low or high frequency, consider whether it is triggered by coughing, straining, or Valsalva maneuver or by exertion or sexual activity or sleep (hypnic headache). High-frequency, short-duration headaches not triggered by these include episodic and chronic CH, episodic and chronic paroxysmal hemicrania, hypnic headache, and SUNCT syndrome. Headaches triggered by cough, exertion, and sexual activity include the disorders named for these triggers.
The approach to differential diagnosis and the precise criteria for each disorder are presented elsewhere.5,69 These algorithms should help neurologists generate differential diagnoses based on the second edition of the IHS criteria.
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