Migraine is a fairly common condition that affects 15 to 20% of the population. In its most characteristic manifestation, which is observed in most cases, it takes the form of particularly sharp headaches. Yet, some migraine subtypes have other serious symptoms that may cause some confusion, but may help us better understand the causes of migraines. One of these subtypes is hemiplegic migraine .
Definition
The term “hemiplegic” indicates that one side of the body is affected by motor weakness. This weakness and its reversibility are the characteristic features of a hemiplegic migraine attack. The International Classification of Headaches takes the description further by including other aura-related symptoms (transient impairment of vision or speech) that may accompany this reversible weakness, as well as the typical time of onset of symptoms and the number of seizures to establish a diagnosis.
Prevalence
If migraine affects 15 to 20% of the population, the prevalence of hemiplegic migraine is much lower. According to one estimate, it affects 0.01% of the population (or one person in 10,000) 1 , and cases are almost evenly distributed between those with a family history and those without (known as sporadic cases).
Features
Hemiplegic migraine is a subtype of migraine with aura . The aura signals an impending migraine attack with distinctive characteristics related to the activation of slow motion in the outer covering of the brain, the cortex. The phenomenon may be reminiscent of a slowly moving electric wave passing through regions of the brain responsible for different functions. Its starting point is usually the occipital region (the back of the brain). People sometimes report visual symptoms ( spots, stars, or dazzling zigzag patterns ) or sensory symptoms ( tingling on the face and hands ) or problems with speech or understanding . The weakness felt in half of the body often occurs after these first symptoms, which usually appear within a few minutes. Confusion and fatigue are also possible. The whole thing is almost always accompanied by headaches, usually acute. The first attack of hemiplegic migraine usually occurs between the ages of 10 and 20 . Patients are therefore often assessed for the first time by pediatricians in the emergency room or by pediatric neurologists.
Any patient with motor weakness on one side of the body is treated as a neurological emergency : this means that there is dysfunction in the half of the brain (the hemisphere) opposite the side displaying the weakness. If the patient is not known to have hemiplegic migraine, then many conditions should be considered as a potential cause: stroke or cerebral hemorrhage (which are unusual, but not impossible in a child) or seizure ( a region of the brain that goes into convulsion can cause tremors on the opposite side of the body followed by transient weakness). When the patient has a history of migraine, especially migraine with aura, the diagnosis of hemiplegic migraine then becomes more likely. That said, tests should still be carried out, in particular brain imaging (computed tomography and magnetic resonance imaging) and an electroencephalogram (which assesses the electrical activity of the brain and can detect any activity associated with a seizure), to rule out more serious problems. Brain imaging is usually normal in patients with hemiplegic migraine.
Occasionally, a perfusion scan is done during the episode to measure blood flow in the brain. In the event of a stroke, such a test would reveal decreased circulation to the affected side. With hemiplegic migraine, several abnormalities have been reported, such as a decrease in the amount of blood flowing to the brain in some patients and an increase in blood volume on the affected side in others, which likely results from dilation ( or swelling) of the vessels seen with migraine (and suspected to contribute to the throbbing pain experienced by many migraine sufferers). Explanations for these seemingly contradictory results could be attributed to the timing of the testing. Indeed, some researchers have posited that the process may involve a momentary decrease followed by an increase in blood flow as compensation. The electroencephalogram may show other abnormalities, but these differ from those seen with seizure disorders.
A hemiplegic migraine attack usually resolves in less than two hours , but some exceptional cases report symptoms extending over several days . Diagnosis is therefore based on the history and on the manifestation of symptoms , after the elimination of other potential causes . In the absence of a family history, the diagnosis will be one of sporadic hemiplegic migraine. The history will lead to a diagnosis of familial hemiplegic migraine, in which case genetic testing may be recommended to determine the type of mutation present in the patient. First elements of genetic response. We’ve known for quite some time that all migraines have a genetic basis. Nearly 38 distinct mutations have a higher prevalence in migraineurs, and many migraineurs carry more than one mutation, which explains the wide variety of forms that the disease takes in different people. Thus, despite the common division between familial and sporadic hemiplegic migraine, genetics is at work in both groups,
Familial hemiplegic migraine is associated with three known mutations. All of these mutations affect the functions of ion channels, proteins that act as miniature gateways allowing electrically charged particles (such as sodium, calcium and chloride) to enter nerve cells. This mechanism is vital for the activity of nerve cells. Studies are underway to determine other mutations that may cause familial hemiplegic migraine. These genetic mutations are transmissible in a very large proportion. Indeed, people with familial hemiplegic migraine will pass it on to their offspring in 50% of cases (a bit like a coin toss). A person who inherits the gene will not automatically develop the disease, but 70-90% of people who carry one of the identified genes and have a family history will experience symptoms of hemiplegic migraine. (Sutherland HG et al. J Headache Pain 2019) Most patients diagnosed with hemiplegic migraine have nono family history , but they may still be carriers of known mutations (history data is not always accurate, and the genetic mutation is not necessarily expressed in all carriers).
Evolution
Hemiplegic migraine attacks tend to become less frequent and less virulent with age . They can be brought on by head trauma, viral infections, or intense emotional stress .
Treatment
Given the high rarity of hemiplegic migraine, there are few data on the optimal treatment of this disease. In general, patients are excluded from drug trials, and many doctors avoid the use of triptans (an interruptive treatment for migraine) for fear of creating blood circulation problems, but no serious studies show that these patients have higher risk of stroke. During an acute attack, patients receive symptomatic treatment, such as intravenous hydration and headache relief treatments .
There is no clear guidance on the most effective preventive medications. Most medical articles are about single people or small groups. A calcium channel blocker, verapamil , has been used with some success, as have some drugs that are not commonly used with migraine, such as acetazolamide .
1. Thomsen L et al. Cephalalgia. 2002;22(5):361.
2. Roth C, et al. Multimodal imaging findings during severe attacks of familial hemiplegic
migraine type 2. J Neurol Sci. 2018;392:22–7.