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What is a Familial Hemiplegic Migraine?

By EC Rosenberg
Updated Mar 03, 2024
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Familial hemiplegic migraine, also known as FHM, is a type of relatively rare migraine headache that causes weakness or compromised function on one side of the body, or hemiplegia. The migraine is considered familial because it has a genetic component and thus runs in families; it should be noted, the symptoms are often indistinguishable from a non-genetic form of the disorder called Sporadic Hemiplegic Migraine (SHM). Familial hemiplegic migraine is among the more severe forms of migraine, with a wider array of symptoms and longer-lasting residual effects.

Symptoms of familial hemiplegic migraines can be similar to those of a classic migraine, which can include visual auras prior to onset, headache, sensitivity to light or sound, and nausea or vomiting. Most classic migraines, however, do not include the signature hemiplegia of familial hemiplegic migraines. Symptoms also may include ataxia, or overall muscle weakness; mental confusion; visual disturbance; and sometimes sudden onset, which can mimic a stroke. In a classic migraine, symptoms usually stop at the end of the attack, but some symptoms of familial hemiplegic migraine can continue for hours or even days after the end of the migraine itself. The migraine can also present without headache. While most classic migraines begin around puberty or adolescence, familial hemiplegic migraine can occur even in infants, usually presenting as convulsions. This type of migraine also may begin to dissipate during menopause, while classic migraines can often be lifelong.

Propensity toward any kind of migraine is usually genetic, but familial hemiplegic migraine is carried in an autosomal dominant gene, meaning that you need only one parent with the dominant gene in order to carry the disorder. Diagnosis of familial hemiplegic migraine typically requires that a patient exhibit most of the symptoms associated with SHM, and have at least one first-degree relative—a parent, child, or sibling—suffering from symptoms. Genetic testing for familial hemiplegic migraine involves identification of mutations on the ATP1A2, CACNA1A, and SCN1A genes. Researchers have discovered three slightly different forms of the migraine, known as FHM-1, -2, and -3. Each form maps to the mutation of an individual gene.

Familial hemiplegic and SHM migraines are more severe and potentially more dangerous than classic migraines, and thus careful thought and care should be put into their prevention and treatment. Most migraine attacks are caused by a combination of external and internal triggers. Some triggers, such as emotional stress, can difficult to avoid; others, such as alcohol use, are easily avoided. Migraine medications typically fall into three categories: preventative medications work to stop migraines before they start; abortive treatments attempt to stop migraines during an attack; and rescue medication is usually a form of analgesic and works to relieve or mask the pain until an attack has passed. Patients should discuss options with their doctors, particularly as abortive medications can lose their effectiveness over time.

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