EPIDEMIOLOGY OF THE CHRONIC DAILY HEADACHE

The epidemiology of CDH has been described in a number of population samples based in Europe, Asia, and the United States (Table 58-2).^3,^4,^10,¹¹ The prevalence of CDH is remarkably consistent among studies, ranging from 2.4% (Norway) to 4.7% (Spain). In the United States, the prevalence is 4.1%. From 35% to 50% of CDH sufferers in the population have transformed migraine.

TABLE 58-2 Prevalence of Very Frequent Headaches in Adult Populations According to Silberstein’s and Lipton’s ² Criteria

The incidence of CDH was investigated in a prospective study in the United States. Among subjects with episodic headaches at baseline, 3% developed CDH within 1 year.¹² The incidence among migraine sufferers in subspecialty care is 13%.

Clinic-based studies show that CDH affects up to 80% of the patients presenting in a headache clinic.¹³^–¹⁶ In this setting, transformed migraine is by far the most common type of CDH. In a study by Mathew and associates,¹⁴ 77% of the patients with CDH had transformed migraine. In our clinic, transformed migraine represented 87.4% of the cases of CDH seen in a headache specialty center.¹³

CLINICAL CHARACTERIZATION

Transformed Migraine/Chronic Migraine

Patients with transformed migraine have a history of migraine. Sufferers usually report a process of transformation over months or years, and as headache frequency increases, associated symptoms become less severe and frequent.¹³^–¹⁶ The process of transformation frequently ends in a pattern of daily or nearly daily headache that resembles CTTH, with some attacks of full migraine superimposed.² In the clinical setting, migraine transformation is most often related to acute medication overuse, but transformation may occur without overuse.¹⁷ In the general population, most cases of transformed migraine are not related to medication overuse.¹² Multiple risk factors may be involved in these cases (see section risk factors for the development of CDH).

The International Headache Society proposed criteria for the diagnosis of transformed migraine: (1) Headache frequency is 15 days or more per month for 3 months or more, with an average headache duration of more than 4 hours/day (if untreated); (2) the headache fulfills criteria for migraine without aura, on 8 or more of the headache days; and (3) the headache does not meet criteria for CTTH, hypnic headache, hemicrania continua, or NDPH (Table 58-3).

TABLE 58-3 Diagnostic Criteria for Primary Chronic Daily Headaches According to the International Classification of Headache Disorders (2004) Criteria and Silberstein’s and Lipton’s ² Criteria

Headache	S-L–AHS	ICHD-II
Transformed migraine/chronic migraine	Transformed Migraine Headache frequency ≥15 days/month for 3 months Average headache duration of ≥4 hours/day (if untreated) Headache fulfilling HIS criteria for migraine without aura (1.1), migraine with aura (1.2), or probable migraine (1.6), on ≥50% of the headache days Does not meet criteria for IHS chronic tension-type headache (2.3), hypnic headache (4.5), hemicrania continua (4.7) or new daily persistent headache (4.8) Not attributed to another disorder	Chronic Migraine (Appendix) Description: Migraine headache ≥15 days per month for ≥3 months and no drug overuse Diagnostic criteria: Headache fulfilling criteria C and D for migraine without aura (1.1) on ≥18 days/month for >3 months Not attributed to another disorder
Chronic tension-type headache	Average headache frequency ≥15 days/month (180 days/year) for ≥6 months and fulfilling the next three criteria: At least two of the following pain characteristics: 1. Pressure or tightening quality 2. Mild or moderate severity (may inhibit but does preclude activities) 3. Bilateral location 4. No aggravation by walking stairs or similar routine physical activity Both of the following: 1. No vomiting 2. *** No more than one of the following: nausea, photophobia, phonophobia	At least 10 episodes fulfilling the next five criteria; number of days with such headache ≥15 days per month for at least 3 months (≥180 days per year) continuously Headache lasts hours or may be continuous; at least two of the following pain characteristics: 1. Pressing/tightening (nonpulsating) quality 2. Mild or moderate intensity (may inhibit but does not preclude activities) 3. Bilateral location 4. No aggravation by walking stairs or similar routine of physical activity Both of the following: 1. No more than one of the following: photophobia, phonophobia, or mild nausea 2. No moderate or severe nausea and no vomiting Use of analgesics or other acute medication on ≤10 days per month Not attributed to another disorder
New daily persistent headache	Average headache frequency >15 days/month for >1 month Average headache duration >4 hours/day (if untreated); frequently constant without medication but may fluctuate No history of tension-type headache or migraine which increases in frequency and decreases in severity in association with the onset of new daily persistent headache (over 3 months) Acute onset (developing over <3 days) of constant unremitting headache Headache is constant in location (needs to be tested) Does not meet any criteria for hemicrania continua (4.8)	Headache that, within 3 days of onset, fulfills the next three criteria: Headache is present daily, and is unremitting, for >3 months At least two of the following pain characteristics: 1. Bilateral location 2. Pressing/tightening (nonpulsating) quality 3. Mild or moderate intensity 4. Not aggravated by routine physical activity such as walking or climbing Both of the following: 1. No more than one of the following: photophobia, phonophobia, or mild nausea 2. Neither moderate or severe nausea nor vomiting Not attributed to another disorder
Hemicrania continua	Headache present for at least 1 month and fulfilling the next three criteria: Unilateral headache Pain has all three of the following qualities: 1. Continuous but fluctuating severity 2. Pain exacerbations of at least moderate severity 3. Lack of precipitating mechanisms Either absolute response to indomethacin or one of the following features with severe pain exacerbation: 1. Conjunctival injection 2. Lacrimation 3. Nasal congestion 4. Rhinorrhea 5. Ptosis 6. Eyelid edema 7. Idiopathic stabbing headache	Headache present for at least 2 months and fulfilling the next four criteria: Unilateral headache without side shift Pain has the following qualities: 1. Daily and without pain-free periods 2. Moderate severity but with exacerbations when it becomes severe Complete response to indomethacin At least one of the following autonomic features in association with exacerbations of pain on the affected side: 1. Conjunctival injection and/or lacrimation 2. Nasal congestion and/or rhinorrhea 3. Ptosis and/or miosis Not attributed to another disorder

ICHD-II, International Classification of Headache Disorders, 2nd ed.; IHS, International Headache Society; S-L, Silberstein and Lipton.

The terms transformed migraine and chronic migraine have been used synonymously in the past, but this is no longer appropriate: Chronic migraine has a specific definition in the ICHD-II, which does not recognize transformed migraine as a separate entity.⁸ One main difference exists between the S-L–AHS (transformed migraine) and ICHD-II (chronic migraine) systems: The ICHD-II criteria for chronic migraine require that headaches meeting criteria for migraine without aura occur on at least 15 days a month. To classify transformed migraine, the S-L–AHS criteria require at least 15 days of headache (not necessarily migraine), in which at least 50% of the days fulfill criteria for migraine or probable migraine.

Chronic Tension-Type Headache

CTTH (see Table 48-3) represents one half of the CDH cases found in population studies but just a small fraction of those found in specialty clinics. It is the only CDH that was addressed by the ICHD-I as a single diagnosis.⁷ The criteria remained little changed in the ICHD-II.⁸ Despite the International Headache Society criteria distinguishing between episodic headache and CTTH, this headache remains surprisingly poorly studied. This can be explained partially by the confusion between CTTH and transformed migraine with a low frequency of superimposed migraine attacks.

The prevalence of CTTH is markedly lower than that of episodic tension-type headache (ETTH), the most prevalent primary headache disorder. Its 1-year prevalence estimates range from 1.7% to 2.2%.^18,¹⁹ The female preponderance of CTTH is greater than that of ETTH. In the United States, the prevalence of CTTH was reported to be 2.8 among women and 1.4 among men, with an overall gender prevalence ratio of 2.0.²⁰ The prevalence of CTTH increases with age.

The distinguishing pain features of CTTH are bilateral location, nonpulsating quality, mild to moderate intensity, and lack of aggravation by routine physical activity. The pain is not accompanied by nausea, although the presence of either photophobia or phonophobia (but not both) does not exclude the diagnosis.

If the CDH develops abruptly (de novo), patients are said to have NDPH.

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