Chronic migraine, classification, differential diagnosis, and epidemiology

Chronic migraine (CM) is the most disabling of the 4 types of primary chronic daily headache (CDH) of long duration, a syndrome defined by primary headaches 15 or more days per month for at least 3 months with attacks that last 4 hours or more per day on average. CDH of long duration includes CM, chronic tension-type headache, new daily persistent headache, and hemicrania continua. CM affects approximately 2% of the adult population in Western countries, imposing substantial burdens on individual sufferers and their families and, more broadly, upon society. Although this disorder is highly disabling and prevalent, it remains largely underdiagnosed and undertreated. Diagnosing CM requires a systematic approach that includes these steps: (1) exclude a secondary headache disorder, and (2) diagnose a specific primary headache syndrome based on frequency and duration, for example, short-duration episodic, long-duration episodic, or long-duration chronic. CM usually develops as a complication of episodic migraine after a period of increasing headache frequency. This migraine transformation is associated with a number of risk factors, some of which cannot be modified, including age and race. Other risk factors for CM are modifiable, such as obesity, snoring, head injury, stressful life events, and overuse of opioids and barbiturates. However, risk factor modification has not yet been shown to decrease the likelihood of CM onset. According to a cross-sectional analysis of data from the American Migraine Prevalence and Prevention study published this year in Journal of Neurology, Neurosurgery, and Psychiatry, when compared to patients with episodic migraine, patients with CM were significantly less likely to be employed full-time and almost twice as likely to be occupationally disabled. In addition, patients with CM were nearly twice as likely to have anxiety, chronic pain, or depression. Furthermore, patients with CM had higher cardiovascular and respiratory risk, were 40% more likely to have heart disease and angina, and were 70% more likely to have a history of stroke. These findings highlight the paramount importance of clinical vigilance, accurate diagnosis, and appropriate, effective management - including treatment or referrals - to improve patient outcomes.