Chronic migraine
Chronic neurological disorder characterized by recurrent moderate to severe headaches often in association with a number of autonomic nervous system symptoms. The word derives from the Greek ἡμικρανία (hemikrania), “pain on one side of the head”, from ἡμι- (hemi-), “half”, and κρανίον (kranion), “skull”.
Epidemiology
Chronic migraines (CM) affect approximately 2% of the population, resulting in significant disability, economic burden, and impairments in quality of life. Historical neurosurgical procedures, such as lesioning of the trigeminal dorsal root entry zone or neurolysis of the occipital nerve, have not gained favor because of procedural morbidity and poor durability, respectively. Occipital nerve stimulation is emerging as a potentially promising modality for the treatment of CM, with greater than 50% pain reduction in approximately 80% of patients in open-label trials and ∼40% of patients in randomized controlled trials. Mechanisms of neuromodulation remain unclear 1).
Classification
Clinical Features
Typically the headache affects one half of the head, is pulsating in nature, and lasts from 2 to 72 hours. Associated symptoms may include nausea, vomiting, and sensitivity to light, sound, or smell. The pain is generally made worse by physical activity.
Up to one-third of people with migraine headaches perceive an aura: a transient visual, sensory, language, or motor disturbance which signals that the headache will soon occur.
Occasionally an aura can occur with little or no headache following it.
Migraines are believed to be due to a mixture of environmental and genetic factors.About two-thirds of cases run in families.
Changing hormone levels may also play a role, as migraines affect slightly more boys than girls before puberty, but about two to three times more women than men.
The risk of migraines usually decreases during pregnancy.
The exact mechanisms of migraine are not known. It is, however, believed to be a neurovascular disorder.
The primary theory is related to increased excitability of the cerebral cortex and abnormal control of pain neurons in the trigeminal nucleus of the brainstem.
Molecular mechanisms
Its molecular mechanisms remain poorly understood. There is some debate about whether migraine is a disease of vascular dysfunction or a result of neuronal dysfunction with secondary vascular changes. Genome-wide association (GWA) studies have thus far identified 13 independent loci associated with migraine. To identify new susceptibility loci, Gormley et al carried out a genetic study of migraine on 59,674 affected subjects and 316,078 controls from 22 GWA studies. We identified 44 independent single-nucleotide polymorphisms (SNPs) significantly associated with migraine risk (P < 5 × 10-8) that mapped to 38 distinct genomic loci, including 28 loci not previously reported and a locus that to our knowledge is the first to be identified on chromosome X. In subsequent computational analyses, the identified loci showed enrichment for genes expressed in vascular and smooth muscle tissues, consistent with a predominant theory of migraine that highlights vascular etiologies 2).
Complications
Treatment
see Migraine treatment.
Systematic review and meta-analysis
Naghdi et al. identified, reviewed, and extracted data from randomized controlled trials (RCTs) of preventive drugs for chronic migraine with at least 200 participants. Data were analysed using network meta-analysis.
They included 12 RCTs of six medications (Eptinezumab, Erenumab, Fremanezumab, Galcanezumab, Onabotulinumtoxin A, and Topiramate) compared to placebo or each other. All drugs effectively reduced monthly headache and migraine days compared with placebo. The most effective drug for monthly headache days was Eptinezumab 300mg, with a mean difference of -2.46 days, 95% Credible Interval (CrI): -3.23 to -1.69. On the Surface Under the Cumulative Ranking Area (SUCRA) analysis, the probability that Eptinezumab 300mg was ranked highest was 0.82. For monthly migraine days, the most effective medication was Fremanezumab-monthly, with a mean difference: -2.77 days, 95% CrI: -3.36 to -2.17, and 0.98 probability of being ranked the highest. All included drugs, except Topiramate, improved headache-related quality of life. No eligible studies were identified for the other common preventive oral medications such as Amitriptyline, Candesartan, and Propranolol. The main reasons were that the studies did not define chronic migraine, were undertaken before the definition of chronic migraine, or were too small.
All six medications were more effective than the placebo on monthly headache and migraine days. The absolute differences in the number of headache/migraine days are, at best, modest. No evidence was found to determine the relative effectiveness of the six included drugs with other oral preventive medications.
Registration: PROSPERO (number CRD42021265990) 3).