Etiology
The last few decades have brought a better understanding of the etiology and pathophysiology of migraine. Genetic, environmental, and other unknown factors are responsible for central nervous system hyperexcitability, leading to a susceptibility to episodic decompensation characterized by headache and other associated symptoms.
Pathophysiology
The pathophysiology of migraine remains poorly understood despite recent progress. Various aspects of the migraine attack are now more or less explained; however, a unifying, overarching pathophysiologic process remains elusive.
A genetic predisposition for generalized neuronal hyperexcitability in migraine is well accepted, as a family history of migraine is found in approximately 50% of patients.[8] Leaving aside the rare monogenic hemiplegic migraine forms, migraine is considered to be a polygenic, epigenetic condition. Genes encoding various ion channels (e.g., CACNA1A, ATP1A2, PRRT2, and SCN1A) have been associated with familial hemiplegic migraine.[1]
Migraine attacks have the following phases: premonitory, aura, ictal, postdromal, and interictal. Each of these phases has its own set of pathophysiologic pathways, more or less understood.[9]
Some migraine patients report a premonitory phase that precedes the onset of headache by up to a few days, and that consists of fatigue, yawning, neck stiffness, mood changes, food cravings, muscle aches, and photophobia, among other symptoms.[10] The mechanistic basis of such a wide array of symptoms is unknown. Functional neuroimaging studies support the role of the hypothalamus in the initiation of the migraine attack.[11][12] One hypothesis suggests that the hypothalamus and other cortical and subcortical areas are activated by various migraine triggers (smell, awakening, etc.). The hypothalamus exerts activatory influences on the parasympathetic system, leading to cerebral vasodilation and the release of inflammatory molecules, ultimately leading to meningeal nociceptor activation and headache.[13] Another hypothesis suggests that the hypothalamus and brainstem exert excitatory and inhibitory influences on the thalamic relay for the nociceptive trigeminovascular signals.[14]
The aura phase consists of self-resolving, cortical neurologic manifestations such as visual or sensory symptoms that most often precede the onset of a headache. It is believed to be the result of the cortical spreading depression, a slowly advancing wave of depolarization followed by hyperpolarization.[15]
The headache itself dominates the ictal phase. The researchers noted that activating the trigeminovascular pathway is the basis of the ictal phase and explains the throbbing, pulsating type of headache characteristic of migraine. It is unclear what is responsible for stimulating the meningeal and large intracranial arteries' nociceptors.
The postdrome phase describes the period between headache resolution and complete recovery. Many patients report fatigue and concentration difficulties during this period.[16]
Classification
International Classification of Headache Disorders, 3rd edition (ICHD-3)[1]
1.1 Migraine without aura: recurrent headache disorder manifesting in attacks lasting 4-72 hours. Typical characteristics of the headache are unilateral location, pulsating quality, moderate or severe intensity, aggravation by routine physical activity, and association with nausea and/or photophobia and phonophobia.
1.2 Migraine with aura: recurrent attacks, lasting minutes, of unilateral fully reversible visual, sensory, or other central nervous system symptoms that usually develop gradually and are usually followed by headache and associated migraine symptoms.
1.2.1 Migraine with typical aura: migraine with aura, in which aura consists of visual and/or sensory and/or speech/language symptoms, but no motor weakness, and is characterized by gradual development, duration of each symptom no longer than 1 hour, a mix of positive and negative features, and complete reversibility
1.2.1.1 Typical aura with headache
1.2.1.2 Typical aura without headache.
1.2.2 Migraine with brainstem aura: migraine with aura symptoms clearly originating from the brainstem, but no motor weakness.
1.2.3 Hemiplegic migraine: migraine with aura including motor weakness
1.2.3.1 Familial hemiplegic migraine (FHM)
1.2.3.1.1 Familial hemiplegic migraine type 1 (FHM1)
1.2.3.1.2 Familial hemiplegic migraine type 2 (FHM2)
1.2.3.1.3 Familial hemiplegic migraine type 3 (FHM3)
1.2.3.1.4 Familial hemiplegic migraine, other loci
1.2.3.2 Sporadic hemiplegic migraine (SHM).
1.2.4 Retinal migraine: repeated attacks of monocular visual disturbance, including scintillations, scotomata, or blindness, associated with migraine headache.
1.3 Chronic migraine: headache occurring on 15 or more days/month for more than 3 months, which, on at least 8 days/month, has the features of migraine headache.
1.4 Complications of migraine
1.4.1 Status migrainosus: a debilitating migraine attack lasting for more than 72 hours
1.4.2 Persistent aura without infarction: aura symptoms persisting for 1 week or more without evidence of infarction on neuroimaging
1.4.3 Migrainous infarction: one or more migraine aura symptoms occurring in association with an ischemic brain lesion in the appropriate territory demonstrated by neuroimaging, with onset during the course of a typical migraine with aura attack
1.4.4 Migraine aura-triggered seizure: a seizure triggered by an attack of migraine with aura.
1.5 Probable migraine: migraine-like attacks missing one of the features required to fulfill all criteria for a type or subtype of migraine coded above, and not fulfilling criteria for another headache disorder
1.5.1 Probable migraine without aura
1.5.2 Probable migraine with aura.
1.6 Episodic syndromes that may be associated with migraine
1.6.1 Recurrent gastrointestinal disturbance
1.6.1.1 Cyclical vomiting syndrome
1.6.1.2 Abdominal migraine
1.6.2 Benign paroxysmal vertigo
1.6.3 Benign paroxysmal torticollis.
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