IHS diagnostic criteria for chronic migraine

A. Headache fulfilling criteria C and D for 1.1 Migraine without aura on ≥15 days per month for >3 months

B. Not attributed to another disorder (31)

When medication overuse is present and fulfills criterion B for any of the subforms of 8.2 Medication-overuse headache, it is uncertain whether criterion B is fulfilled until 2 months after medication has been withdrawn without improvement (see Comments).

Most cases of chronic migraine start as 1.1 Migraine without aura. As chronicity develops, headache tends to lose its attack-wise (episodic) presentation. Medication overuse, when present, is the most likely cause of chronic headache. Therefore, the default rule is to code such patients according to the antecedent migraine subtype (usually 1.1 Migraine without aura) plus 1.6.5 Probable chronic migraine plus 8.2.7 Probable medication-overuse headache. When these criteria are still fulfilled 2 months after medication overuse has ceased, 1.5.1 Chronic migraine plus the antecedent migraine subtype should be diagnosed, and 8.2.7 Probable medication-overuse headache discarded. If at any time sooner they are no longer fulfilled because improvement has occurred, code for 8.2, Medication-overuse headache plus the antecedent migraine subtype, and discard 1.6.5 Probable chronic migraine.

Since chronic migraine is a newly defined entity, epidemiologic studies using the ICHD-2 criteria are not yet available. Chronic daily headache (CDH) is a collective term, not a diagnosis. It includes chronic migraine, chronic tension-type headache (CTTH), medication-overuse headache, and new daily persistent headache. Some previous studies of CDH have subdiagnosed and thus may allow a qualified guess about chronic migraine. However, these studies used the concept of transformed migraine, which, again, is difficult to translate into chronic migraine, because it does not distinguish medication-overuse headache. In the absence of more specific data, we make use of previous data on CDH and transformed migraine.

In population-based surveys, CDH occurred in 4.1% of Americans, 4.35% of Greeks, 3.9% of elderly Chinese, and 4.7% of Spaniards. Scher et al. ascertained the prevalence of CDH in 13,343 individuals aged 18 to 65 years in Baltimore County, Maryland. The overall prevalence of CDH was 4.1% (5% women, 2.8% men; 1.8:1 women-to-men ratio). More than half (52% women, 56% men) met criteria for CTTH (2.2%); almost one-third (33% women, 25% men) met criteria for transformed migraine (TM) (1.3%); and the remainder (15% women, 19% men) were unclassified (0.6%). Overall, 30% of women and 25% of men who were frequent headache sufferers met IHS criteria for migraine (with or without aura).

Castillo et al. (6) sampled 2252 subjects over 14 years of age in Cantabria, Spain. Overall, 4.7% had CDH: None had hemicrania continua (HC), 0.1% had new daily persistent headache (NDPH), 2.2% had CTTH, and 2.4% had TM. Acute medication overuse occurred in 19% of CTTH and
31.1% of TM patients. Eight patients had a previous history of migraine without aura and now had CDH with only the characteristics of TTH. These headaches met the criteria of TM but could have been migraine and coincidental CTTH.

Wang et al. (37) found that 3.9% of elderly Chinese (over 65 years of age) had CDH. Significantly more women than men had CDH (5.6% and 1.8%, respectively; p <0.001). Of the CDH patients, 42 (70%) had CTTH (2.7%), 15 (25%) had TM (1%), and 3 (5%) had other CDH. Significant risk factors for CDH included analgesic overuse (OR = 79), a history of migraine (odds ratio, OR = 6.6), and a Geriatric Depression Scale-Short Form score of 8 or above (OR = 2.6). At follow-up, patients with persistent primary CDH had a significantly higher frequency of analgesic overuse (33% vs. 0%; p = 0.03) and major depression (38% vs. 0%; p = 0.04) (Table 65-1).

Scher et al. (30) described factors that predict CDH onset and remission in an adult population. CDH was more common in women (OR = 1.65 [1.3-2.0]), those previously married (OR = 1.5 [1.2-1.9]), with obesity (body mass index [BMI] >30) (OR = 1.27 [1.0-1.7]), and those with less education. Obesity, high baseline-headache frequency, high caffeine consumption, habitual daily snoring, and stressful life events were significantly associated with new-onset CDH (29). Having less than a high school education was associated with a threefold increased risk of CDH. (OR = 3.56 [2.3-5.6]). (Table 65-1)

Anxiety, depression, panic disorder, and bipolar disease are more frequent in migraineurs than in nonmigraine control subjects (4,22). Since CM is a complication of migraine, one would expect to find a similar or accentuated profile of psychiatric comorbidity in CM patients. Many older studies do not clearly differentiate between CDH subtypes. In clinic-based samples, depression occurs in 80% of TM patients. CDH patients had significantly higher Zung and Beck Depression Scale scores than did migraine controls (15,16,19,28). Comorbid depression often improves when the cycle of daily head pain is broken.

Mitsikostas and Thomas (23) found that headache patients had significantly higher average Hamilton rating anxiety and depression scores than did nonheadache controls. Patients with CTTH, mixed headache, or drug abuse headache had the highest Hamilton rating depression and anxiety scores. Verri et al. (36) found current psychiatric comorbidity in 90% of primary CDH patients. Generalized anxiety occurred in 69.3% of patients and major depression in 25%.

Juang et al. (12) investigated the frequency of depressive and anxiety disorders in 261 consecutive CDH patients seen in a headache clinic. TM was diagnosed in 152 patients (58%) and CTTH in 92 (35%). Seventy-eight percent of patients with TM had psychiatric comorbidity, including major depression (57%), dysthymia (11%), panic disorder (30%), and generalized anxiety disorder (8%). The frequency of anxiety disorders was significantly higher in patients with TM after controlling for age and sex.

Peres et al. (25) estimated the prevalence of fibromyalgia (FM) in 101 TM patients and analyzed its relationship to depression, anxiety, and insomnia. FM was diagnosed in 35.6% of cases. FM patients had more insomnia, were older, and their headaches were more incapacitating than patients without FM. Fifty-seven patients (87.7%) had at least mild depression. Depression was also associated with FM (p = 0.007), insomnia (p = 0.043), and disability (p = 0.05).

Peres et al. (26) determined the prevalence of fatigue in 63 TM patients. Fifty-three patients (84.1%) had FSS scores greater than 27. Forty-two patients (66.7%) met the criteria for chronic fatigue syndrome established by the Centers for Disease Control. Fatigue as a symptom and chronic fatigue syndrome as a disorder were both common in TM patients.

Underlying the pathophysiology of chronic migraine is, of course, the disposition to migraine without aura. This is discussed extensively in previous chapters of this book. Here, we focus on the question of why some migraine sufferers progress to become chronic. In this discussion, we disregard medication overuse, which is by far the most common cause of chronicity. Recent work suggests several mechanisms that could contribute: (1) increased peripheral nociceptive activation (perhaps due to chronic neurogenic inflammation) and activation of silent nociceptors; (2) peripheral sensitization; (3) altered sensory neuron excitability; (4) central sensitization of TNC neurons due to posttranslational changes in ligand- and voltage-gated ion-channel kinetics, altering excitability and strength of their synaptic inputs; (5) phenotype modulation due to alterations in the expression of receptors/transmitters/ion channels in peripheral and central neurons; (6) synaptic reorganization modification of synaptic connections caused
by cell death or sprouting; (7) decreased pain modulation due to loss of local and descending input (39); or (8) a combination of these.