Stroke and migraine
There is considerable interest in the relationship between migraine and stroke. Here we put the relationship into context.
What is a stroke?
A stroke occurs when part of your brain is deprived of its blood supply. There are two main types of stroke, one of which is suggested to have a link with certain types of migraine.
Migraine affects three times the number of women than men. The incidence of stroke in men is twice that of women. Several studies have shown that the risk of ischaemic stroke was increased in women aged 35 to 45 years old who had migraine with or without aura and was exacerbated by oral contraceptive use, smoking and high blood pressure. Ischaemic means a reduced blood and oxygen supply sometimes due to a clot. The other type of stroke is a haemorrhagic stroke, which is where a damaged or weakened artery bleeds into nearby tissue. The link of migraine to this type of stroke is small.
Whilst several studies have shown a relative increased risk of stroke in young women with migraine compared to people without migraine, in absolute terms this risk remains extremely small since stroke is rare in young people.
Is there a risk of stroke during a migraine attack?
Understandably, some people are afraid that their migraine is a symptom of a stroke and others worry that they are more at risk of a stroke during a migraine attack. There is little evidence to suggest that a stroke is more likely to occur during a migraine attack than at another time. Migraine is common. In some people migraine and stroke appear together but the nature of the causal relationship, if any, is difficult to establish firmly. Migrainous infarction is the term given to an ischaemic stroke occurring during a migraine attack.
In this condition aura symptoms are prolonged, and ischaemic stroke is confirmed by being shown in a brain scan. However, research suggests that such a stroke would be independent of the migraine attack. It is also possible for a person to have a stroke but for this to have been mistaken for a migraine attack. The migraine aura can mimic transient ischaemic attacks (TIAs). Conversely, in stroke, headache similar to migraine may occur.
What do the statistics show about migraine and stroke?
Evidence supporting migraine as an independent risk factor for ischemic stroke comes from a review in 2009 that included 25 studies. The following observations were noted:
- In nine studies, relative risk (RR) for ischemic stroke among subjects with any type of migraine was 1.73 compared to those without migraine. The increased risk was largely driven by participants who had migraine with aura. In contrast, the increase in risk for those who had migraine without aura was not statistically significant.
- In studies with available data stratification, the risk of ischemic stroke was significantly increased for the following subgroups:
- Women with migraine but not men
- Subjects with migraine <45 years of age
- Smokers who had migraine with aura
- Women currently using oral contraceptives who had migraine with aura.
The relationship of migraine with hemorrhagic stroke is supported by a review of eight studies which found that the overall effect estimate of hemorrhagic stroke for subjects with any migraine was 1.48.
A review published in 1997 looked at some of the studies in terms of 100,000 women per year. It was suggested that in women under age 35:
- those who do not have migraine and do not take the pill (i.e. the background risk): 1.3 per 100,000 women per year are at risk of stroke
- those who have migraine without aura but don’t take the pill: 4 per 100,000 women per year at risk of stroke
- those who have migraine with aura but don’t take the pill: 8 per 100,000 women per year are at risk of stroke
- those who don’t have migraine and take the pill: 5 per 100,000 women per year at risk of stroke
- those who have migraine with aura and take the pill: 28 per 100,000 women per year at risk of stroke
- those who have migraine without aura and take the pill: 14 per 100,000 women per year are a risk of stroke
To put this into context, other studies have suggested that 8 per 100,000 women per year might die in a road accident and 167 per 100,000 women per year might die from a smoking related problem.
A study in America in 2004, called the Women’s Health Study, looked at 39,754 female health professionals. During the 9 years of the study there were 309 ischaemic strokes in the total population in the study, so there was a total incidence of 8 ischaemic strokes per 100,000 women (0.008%). This includes women with and without migraine aura, so it can be seen that although the relative risk is seemingly high, the actual risk is extremely small. This study confirmed previous studies suggesting that the association between migraine aura and stroke risk was greater in younger than in older women (in this case meaning women under age 55). The higher risk with aura will also include those who have other medical conditions that increase the risk of stroke and which can be associated with aura symptoms rather than true migraine aura. These conditions include some blood clotting disorders and heart conditions. The diagnosis of migraine and migraine aura was self-reported so is subject to bias (that is, there was not an objective person to make the diagnosis).
Why should young women with migraine with aura be at an increased risk of stroke?
The mechanism of the increased risk of ischaemic stroke in young women with migraine remains unknown. It does not seem to be due to an increase in conventional risk factors such as diabetes, high blood pressure and raised cholesterol levels. There are frequent reports of discoveries of differences between people with and without migraine, for example, the recent attention given to patent foramen ovale (PFO) or hole in the heart in patients with migraine with aura. However, these characteristics are not consistently found in people with migraine compared with people without migraine and they show no sex difference, so that they cannot explain why the increased risk of ischaemic stroke in migraine is statistically significant in young women. Some recent studies suggest that aura is associated with adverse cardiovascular risk profile and prothrombotic factors (tendency of blood to clot). Research is continuing to look into this area in the hope of discovering more about the complex relationship between migraine with aura and ischaemic stroke, and any underlying vascular differences between people with and without migraine.
What are the implications?
Whatever the underlying mechanism, the practical implications of the increased ischaemic stroke risk in young women with migraine with aura are relatively clear: when the low absolute risk and its increase by cigarette smoking are taken into account, the first recommendation is not to smoke.
The Faculty of Family Planning and the Family Planning Association guidelines confirm that best practice is to contraindicate the combined contraceptive pill for use by women who have migraine with aura, which is also in line with World Health Organisation recommendations. The risk for women with migraine without aura is lower and other risk factors like smoking are far more likely to increase stroke risk than migraine. However, in practice, given the very low absolute risk of stroke in young women, there is no systematic contraindication to oral contraceptive use but rather a firm recommendation for no smoking and for the use of low oestrogen or progestogen only pills particularly for women with migraine with aura. It is important however that women with migraine who are taking the pill do not decide to suddenly stop taking it without discussing this with their doctor.
Being ‘at risk’ of stroke does not mean dying from a stroke. Around 25% of people who have stroke recover, and another 50% will have a disability after a stroke.
What about older people with migraine?
Migraine is considered to be insignificant as a risk factor for stroke after the age of 50 years. This is because the usual risk factors for ischaemic stroke are high blood pressure, obesity, raised blood cholesterol levels, smoking and older age. These factors tend to combine with each other and, with advancing age, the risk of stroke due to migraine becomes insignificant in comparison with the other risk factors.
Migraine with aura stands out as a stroke risk of young women because it affects people before the usual and more significant age-related factors apply. In addition migraine tends to improve in later life.
- The Stroke Association www.stroke.org.uk