On the surface, strokes and migraines do not seem to have much in common except that both of them can have serious psychological effects on the sufferers. But researchers say that a complex relationship exists between the two.

Migraine is a neurological disorder characterized by the occurrence of throbbing and recurring headaches that can be so severe to interfere with the normal day to day life. Stroke is a medical emergency caused by a compromised blood supply to the brain. It could result in brain damage, eventually leading to complications and disability.

Several studies have associated migraine in young adults, especially women, with ischemic stroke. A recent study relates migraine without aura in older people with subclinical stroke.

Understanding migrainous aura and migrainous infarction

Migraine is a complex neurobiological disorder and the understanding of its pathophysiology is still incomplete. Vascular and genetic pathology have been attributed to this disorder. The condition commonly presents in two forms: migraine with aura (MA) and migraine without aura (MO).

The migrainous aura consists of transient focal neurological disturbances presenting in the form of visual, sensory or motor symptoms that precede the migraine headache. According to the description given by the International Headache Society (IHS), the aura develops gradually over a period of five minutes and it lasts less than 60 minutes. It occurs in up to 25% of migraine sufferers.

The migrainous aura was earlier suspected to be a vascular process (constriction of blood vessels causing the aura and then a reactive vasodilatation causing the headache). But later and recent evidences suggest that the aura may be due to the generation of slowly propagating electrical waves called Cortical Spreading Depression (CSD) that pass through specific parts of the brain including the visual cortex (that part of the cerebral cortex which processes visual signals) and the part of the brain that processes touch signals. This is the reason why aura is often felt as visual disturbances (like seeing sparkles, zigzag patterns, colored and dark spots) and tingling sensations. The CSD is triggered by hypoxic-ischemic stress and it is modulated by genetic and environmental factors.

Migrainous infarction refers to a cerebral infarction that occurs during the course of a typical migraine attack. This may lead to stroke. A typical migrainous infarction is actually rare and it is more common during attacks of migraine with aura than of migraine without aura. One third of the migrainous infarcts are observed in the occipital lobe of the brain, thus explaining the cause for visual deficits that follow the attack. The IHS has established strict guidelines for the diagnosis of migrainous infarction and for this diagnosis to be made, it is necessary that the other possible causes of infarction be ruled out.

Migraine and ischemic stroke

Generally, migraine with aura is associated with an increased risk of ischemic stroke, especially in young women. Most of the studies made a special mention of the increased risk in women who use oral contraceptive pills and who smoke. Though these studies have proposed migraine to be an independent risk factor for stroke in young women, fortunately, they also report that it is only the relative risk that seems to be high (women with migraine aura have an increased risk of developing ischemic stroke when compared to women without migraine aura) but the absolute risk (the overall likelihood of developing ischemic stroke) is actually small.

The actual mechanism for the increased risk of ischemic stroke in people with migraine is not known. Various potential mechanisms have been hypothesized. Cerebrovascular hypoperfusion induced by vasospasm can trigger CSD and this neuronal spreading can itself decrease the perfusion pressure and blood flow to the brain causing ischemia. Increased platelet activation and aggregation and associated blood coagulation abnormalities have also been attributed to the increased risk of ischemic stroke in migraine sufferers. Potential biological mechanisms like endothelial dysfunction (dysfunction of innermost layer of blood vessels) and cervical artery dissection (dissection of arteries in the neck) have also been hypothesized.

All these conditions may lead to the formation of blood clots that can block the blood vessels supplying the brain and cause stroke. Another hypothesis is that the increased prevalence of patent foramen ovale (hole in the heart leading to shunt) in patients with migraine may lead to clot formation and thus stroke. However, it has been difficult to explain a particular reason for the increased risk of stroke in young women with migraine.

Studies suggest a higher risk of silent brain infarction in people with migraine

A recent report suggests that migraine could serve as a risk factor for sub-clinical brain infarctions leading to stroke in older people with migraine. Researchers from the Northern Manhattan Study (NOMAS) reported that migraine sufferers had twice the risk of developing silent stroke when compared to people who did not report migraine episodes. This finding related more to the people who experienced migraine without aura. Having said that, a question arises as to what is a silent stroke?

Silent stroke: unrecognized brain damage, without a warning

Silent stroke does cause permanent damage to the brain, but the damage is small, subtle and goes unnoticed. The reason for this is that silent stroke does not affect the main functional areas of the brain that lead to apparent symptoms when damaged. However, silent strokes can lead to cognitive disturbances and accumulation of such subtle damages can lead to gradual neurological deficits.

Though the researchers from the NOMAS did not consider the risk of developing stroke in migraine sufferers to be significant, the prevalence of silent brain infarcts in these patients has raised concerns. The researchers have emphasized the need for reducing the risk factors of stroke in such people. Similar concerns were also expressed in previous studies. Attention is especially needed to patients who have co-existing vascular risk factors like elevated blood pressure, elevated cholesterol level, diabetes, coronary heart disease, etc.

It has to be noted that a high prevalence of silent infarcts has already been reported in older people and hence the elderly population in general, and those with migraine in particular, need to modify their lifestyle with regards to the physical activity and diet, so that the increased risk of stroke is balanced by proper preventive measures.

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