Definition and Overview
Chronic migraine is a condition in which headaches occur 15 or more days per month for more than three months, with at least 8 of those days exhibiting migraine features [1]. The process by which headache frequency gradually increases in patients who previously had episodic migraine, converting to chronic migraine, is termed "migraine chronification."
Approximately 1.4-2.2% of the adult population worldwide meets the criteria for chronic migraine [2]. Approximately 2.5-3% of episodic migraine patients convert to chronic migraine annually [2]. Chronic migraine causes greater impairment of daily life than episodic migraine, involves more frequent hospital visits, and is commonly accompanied by comorbidities such as depression and anxiety.
Etiology
The causes of migraine chronification are divided into modifiable factors related to lifestyle and non-modifiable factors [2].
Modifiable factors include analgesic overuse (10-15 or more days per month), obesity (BMI 30 or higher, 1.4-fold increased risk), excessive caffeine intake (more than 400mg per day), sleep disorders (insomnia, sleep apnea), stress, and comorbid depression or anxiety [3].
Non-modifiable factors that have been reported include female sex, lower socioeconomic status, history of head trauma, and high baseline headache frequency (10 or more days per month) [2].
Frequent use of analgesics weakens the brain's pain-suppressing function. This leads to heightened pain sensitivity and increased headache frequency [3]. Population-based studies have identified analgesics containing sedative components (2.06-fold risk) and opioid analgesics (1.98-fold risk) as independent risk factors for chronification [3].
Repeated migraine attacks gradually sensitize the brain's pain-processing neurons. These sensitized neurons begin responding to stimuli that would not normally produce pain. Allodynia -- experiencing pain from light touch -- occurs in approximately 60-70% of chronic migraine patients, compared to approximately 30-40% of episodic migraine patients, demonstrating this phenomenon [2].
Neuroimaging studies in chronic migraine patients have reported volume reduction in brain regions involved in pain modulation and increased white matter lesions [2]. Whether these changes are causes or consequences remains to be determined, but they suggest structural alterations in the brain's pain modulation system.
Symptoms
The main symptoms of chronic migraine are as follows.
- Headaches persisting 15 or more days per month
- At least 8 of those days exhibit migraine characteristics: unilateral pulsating pain, moderate to severe intensity, aggravation by routine physical activity
- Hypersensitivity to light or sound
- Accompanying nausea or vomiting
- Allodynia -- pain from light touch (present in approximately 60-70%)
- Fatigue, reduced concentration, mood changes
Approximately 30-50% of chronic migraine patients have comorbid depression, and 30-50% have comorbid anxiety disorders [2].
Diagnosis
The international diagnostic criteria for chronic migraine are as follows [1].
A. Headaches occur 15 or more days per month for more than three months.
B. There have been at least five episodes meeting migraine diagnostic criteria.
C. For more than three months, on at least 8 days per month, headaches meet one of the following: (1) migraine diagnostic criteria, (2) migraine with aura criteria, (3) headaches believed to be migraine and effectively treated with triptans or similar medications.
D. Not better accounted for by another diagnosis.
When analgesic overuse is present, both chronic migraine and medication-overuse headache are diagnosed simultaneously. After discontinuation of analgesic overuse, if headaches decrease to fewer than 15 days per month over a two-month observation period, the diagnosis is reclassified as episodic migraine.
Analgesic overuse is present in approximately 50-80% of chronic migraine patients [1]. Medication-overuse headache is diagnosed when simple analgesics are used 15 or more days per month, or triptans or combination analgesics are used 10 or more days per month for more than three months [1].
Treatment
Analgesic Overuse Discontinuation
The first step in treating chronic migraine with analgesic overuse is discontinuation of the overused medication. Withdrawal symptoms such as rebound headache, nausea, anxiety, and sleep disturbance may occur for 2-10 days after discontinuation, but most resolve within 2-8 weeks. Research indicates that analgesic overuse discontinuation alone achieved a meaningful reduction in headache frequency in approximately 50% of patients [3].
Preventive Pharmacotherapy
Among preventive medications for chronic migraine, topiramate and Botox injection (botulinum toxin type A) have the highest level of evidence [4][5].
Topiramate demonstrated an additional reduction of 3.5 monthly migraine days compared to placebo in clinical trials [5]. Botox injection reduced monthly headache days by an additional 1.4-2.3 days compared to placebo at 12 weeks in large-scale clinical trials, and 24-week treatment resulted in an average reduction of 8-9 monthly headache days from baseline [4].
CGRP (calcitonin gene-related peptide) targeted therapies are a new class of preventive medications that block substances involved in migraine pathogenesis. They are used as additional treatment options for patients with inadequate response to conventional preventive medications.
Neuromodulation Therapy
Prognosis and Complications
Without appropriate treatment, chronic migraine tends to maintain or worsen in headache frequency and intensity. The likelihood of comorbid depression, anxiety disorders, and sleep disturbance increases, and economic losses due to work absenteeism and reduced productivity are approximately 4-5 times greater than for episodic migraine [2].
With appropriate preventive treatment combined with lifestyle modification, headache frequency can be reduced to episodic migraine levels in a substantial number of patients. Improvement has been reported in approximately 50% of patients with analgesic overuse discontinuation alone [3].
Lifestyle Guide
Lifestyle recommendations for chronic migraine management are as follows.
- Limit analgesic use to no more than 2-3 times per week and record the number of days of use in a headache diary.
- Maintain regular sleep habits. Going to bed and waking up at the same time every day is recommended.
- Engage in aerobic exercise for at least 30 minutes, at least three times per week.
- Limit caffeine intake to 200mg or less per day (approximately 2 cups of coffee).
- Practice relaxation techniques or breathing exercises for stress management.
- Keep a headache diary to identify triggers (food, environment, stress, etc.).
- If depression or anxiety persists, seek concurrent psychiatric care.
- If overweight, aim to maintain an appropriate body weight.