It is estimated that about 15-17% of the population experiences migraine headaches. While this number may seem small, the World Health Organization has estimated that percentage to translate into more than 300 million afflicted. For a long time, migraine was merely considered a nuisance malady, which could cause great distress, but was of little threat to one's overall health. In the last four to five years, more and more research has suggested a positive link between migraine headaches and risk of stroke. In 2005, a meta-analysis of the available data suggested that a history of migraines increased stroke risk more than two-fold. It also suggested that patients who suffered from associated auras and women on oral contraceptives were at an even greater risk.
Now, a recent study published in the March issue of the British Medical Journal reports a significant association between migraine in pregnancy and the risk of a pregnancy-related stroke or heart attack.
The study was conducted by Wake Forest University Health Sciences at Winston-Salem, and its goal was to assess the correlation between migraine headaches and cardiovascular diseases in pregnancy. As their subjects, they looked a nationwide inpatient sample from the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality. From 2000-2003, there were 18,345,538 pregnancy-related hospital discharges reported to the database. The authors looked at the endpoints of migraine, stroke and vascular diseases as were reported and identified according to standard ICD-9 diagnosis codes.
Among the samples there were 33,956 migraine codes, about 185 per 100,000 deliveries. Excluding pre-eclampsia, diagnoses that came to be associated with migraines in pregnancy were stroke, myocardial infarction, pulmonary embolus/thromboembolism and hypertension. Other associated entities were pre-eclampsia, gestational diabetes, and smoking.
The large size of the study gives it great statistical power; however, the limitations that do exiat are:
1. There is no determination in this database of which diagnosis came first, migraine or the
vascular malady. Consequently, prospective studies will be needed;
2. No distinction between migraines with and without aura;
3. Cause and effect not established;
4. Lack of data and research regarding use of drugs to treat cardiovascular risk factors in
pregnancy. With this limitation, there may have been great reluctance to treat pregnant
women whom might have been at risk with standard drugs.
There has been no explanation offered regarding the mechanism by which migraines might increase stroke risk. There still is not even a consensus as to the exact physiologic mechanism of migraines themselves. Many believe that migraines are vascular headaches. Some EEG evidence has suggested that there is an acute depression in brain wave activity and cerebral blood flow prior to a migraine onset. This is then believed to be followed by a sudden dilation and engorgement of the vessels lining the brains surface. As these are in direct contact with the meningeal covering which is rich with sensory innervation, it is believed that the pressure from the engorgement may cause severe pain. On the other hand, some believe that it is not a vascular event at all, but is related to some misfiring of the tri-geminal nerve.
What we do know is that this was not the first large study to suggest the relationship between the entities. It is, however, the first to assess the relationship in pregnancy. It specifically says that pregnancy-related migraine may increase the stroke risk 17 fold. Further, the risk of acute myocardial infarction is increased four fold.
Further risk is suggested by the fact that pregnancy itself is associated with a higher incidence of migraine headaches in women whom already suffer. Therefore, the stroke risk is even further compounded in pregnancy. Lastly, stroke is always a risk, as is any other clotting event like a DVT or PE due to the high levels of estrogen, which make the blood more likely to clot.
If these studies are accurate, then migraine headaches in pregnant women will take on a whole new meaning, as they would put her into a high risk category. Given the frequency of it, it would be imperative for us to embark upon discovering new and safe ways to protect her and her fetus from a devastating event. It would also compel pharmaceutical companies to develop more drugs that are known to be safe in pregnancy which could decrease the risk of disease. Right now, short of certain anti-hypertensives and a blood-thinner called Lovenox, there is not much available to us in these instances.