Chronic Migraine: Epidemiology, Mechanisms, and Treatment

Chronic migraine is a debilitating primary headache disorder associated with high personal, familial, and social impact. The diagnosis is made when there are at least 15 headache days monthly including 8 migraine days per month for at least 3 months. The prevalence is 1.4–2.2% in the population. Among individuals diagnosed with chronic migraine, there may be significant variability in headache days with a potential to remit, remain unchanged, or progress to even greater disability. Most chronic migraine progresses from episodic migraine, with several identified risk factors for chronic migraine and migraine progression. The exact mechanism of chronic migraine is unknown but is associated with an increased cortical excitability, central sensitization, alternations in nociceptive signaling, as well as physiological, structural, and functional brain changes. There is evidence for both nonpharmacological and pharmacological treatment options to restore function. The best currently established pharmacologic evidence for the treatment of chronic migraine is onabotulinumtoxinA and topiramate. Behavioral treatments may improve headache symptoms and comorbidities. Emerging data shows potential benefit for neurostimulation, and large well-designed studies are needed. Multicenter randomized placebo-controlled studies of monoclonal antibodies to the calcitonin gene-related peptide, or its receptor, have demonstrated efficacy, tolerability, and safety. Biomarkers are needed to guide prognosis, treatment response, and clinical trials. The concept and management of refractory chronic migraine is discussed, and clinically meaningful endpoints are reviewed