Familial Hemiplegic Migraine

Familial hemiplegic migraine (FHM) is a rare form of hemiplegic migraine. It is unique because it is the only type of migraine scientifically confirmed to run in families. Familial hemiplegic migraines are a subtype of migraine with aura.1

FHM is a very rare condition found in 1 of every 10,000 people worldwide. It is more common in women than men, and attacks often begin in childhood or the teenage years. Attacks tend to happen less often after age 50.1

Symptoms of familial hemiplegic migraine

Familial hemiplegic migraine shares many of the same symptoms as other forms of migraine with aura. The aura symptoms begin gradually over 5 minutes or longer, and occur 1 after another. Each symptom lasts 5 minutes to 1 hour, except for the muscle weakness, which can last up to 3 days. Symptoms of a hemiplegic migraine may include:1,,2

  • Muscle weakness that goes away after the migraine attack and often occurs on 1 side of the body. (This is the key symptom of a hemiplegic migraine.)
  • Vision changes, such as seeing flickering lights, spots, or lines
  • Part or full loss of eyesight
  • Trouble speaking that goes away after the migraine attack
  • Head pain

Difference between hemiplegic migraine and other types

The main difference between a hemiplegic migraine and other types of migraine is the muscle weakness that completely disappears after the attack ends. This is called motor aura.

People with familial hemiplegic migraine sometimes report more unusual or severe migraine symptoms, including:3

  • Fever
  • Seizures
  • Muscle weakness that lasts days or weeks
  • Coma

Most people with FHM recover completely between attacks. However, some have longer-term problems, such as memory loss, attention problems, problems coordinating movement, or rapid, uncontrolled eye movements.3

Diagnosing familial hemiplegic migraine

Motor aura is 1 key requirement for FHM diagnosis because this symptom does not occur with any other type of migraine. Someone with FHM must have a close family member who also has hemiplegic migraine. Other types of migraine do not count for this diagnosis. This family member must be either a first-degree relative (parent, sibling, or child) or second-degree relative (uncle, aunt, nephew, niece, grandparent, grandchild, or half-sibling).

In addition, the International Headache Society says that to be diagnosed with familial hemiplegic migraine, the person must have at least 2 migraine attacks with motor aura plus at least 1 typical aura symptom.2

In addition, the 2 attacks must also:2

  • Have at least 1 aura symptom that spreads gradually over 5 minutes or longer
  • Two or more aura symptoms happen 1 after the other
  • Each non-motor aura symptom lasts between 5 minutes and 1 hour
  • Muscle weakness (motor aura symptoms) last up to 3 days
  • At least 1 aura symptom takes place only on 1 side of the body
  • Aura symptoms occur with head pain, or head pain follows within 1 hour

Causes of familial hemiplegic migraine

Doctors know of at least 3 specific genetic mutations that cause FHM and believe there are probably more. FHM is an autosomal dominant disorder, which means you only need to inherit the altered gene from 1 parent. This also means a parent with FHM has a 50 percent chance of passing it along to their children.3

Types of familial hemiplegic migraine

The 4 types of familial hemiplegic migraine are based on the 4 genetic mutations and are named:1-3

  • FHM1, which is caused by a mutation in the CACNA1A gene
  • FHM2, which is caused by a mutation in the ATP1A2 gene
  • FHM3, which is caused by a mutation in the SCN1A gene
  • FHM4: Unknown mutation but family history of FHM

The fourth type, FHM4, is diagnosed if genetic testing does not reveal a known mutation but the person has a close family member with hemiplegic migraine. Doctors believe they will eventually find other gene mutations that cause FHM in these families.

Treating familial hemiplegic migraine

Familial hemiplegic migraine is treated with many of the same drugs used for other migraine types. However, abortive or preventive drugs that cause the blood vessels to narrow may be avoided. Triptans are an example of this type of drug.1,3

Avoiding triggers is another key treatment. Many of the potential triggers for FHM attacks are similar to other types of migraine with aura, such as stress, bright lights, lack of sleep, not eating, and eating certain foods and drinks. It is also possible for FHM attacks to be triggered by mild head trauma, so people with FHM may be told to avoid contact sports.3

Ruling out other conditions

A physical exam, medical history, family medical history, and a migraine diary help your doctor diagnose familial hemiplegic migraine. Blood and imaging tests may be ordered to rule out other health conditions, such as stroke, epilepsy, meningitis, or brain tumors. Genetic testing may help if there is a family history of hemiplegic migraines.3

Because muscle weakness, vision changes, difficulty speaking, and head pain are also signs of a stroke, the first time someone experiences these symptoms they must seek immediate medical attention. Some people are also misdiagnosed with epilepsy or stroke.

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Written by: Jessica Johns Pool | Last reviewed: October 2020