Familial hemiplegic migraine (FHM)

Last edited 11/2020 and last reviewed 01/2023

Hemiplegic migraine is a term used to describe the migraine syndrome that is associated with a weakness or sensory loss of the limbs on one side of the body. The headache usually precedes the weakness by a day or more.

Hemiplegic migraine

• migraine with aura including motor weakness
• A. Attacks fulfilling criteria for migraine with aura and criterion B below
• B. Aura consisting of both of the following:
• fully reversible motor weakness
• fully reversible visual, sensory and/or speech/ language symptoms

Notes:
1. The term plegic means paralysis in most languages, but most attacks are characterized by motor weakness.
2. Motor symptoms generally last less than 72 hours - but, in some cases, motor weakness may persist for weeks

It is always necessary to exclude another possible underlying cause for the hemiplegia such as an angioma.

It is a rare form of migraine.

Familial hemiplegic migraine (FHM)

• migraine with aura including motor weakness, and at least one first- or second-degree relative has migraine aura including motor weakness
• diagnostic criteria:
• A. attacks fulfilling criteria for hemiplegic migraine
• B. at least one first- or second-degree relative has had attacks fulfilling criteria for Hemiplegic migraine.

Specific genetic subforms have been identified:

• in FHM1 there are mutations in the CACNA1A gene (coding for a calcium channel) on chromosome 19
• in FHM2 there are mutations in the ATP1A2 gene (coding for a K/Na-ATPase) on chromosome 1
• in FHM3 there are mutations in the SCN1A gene (coding for a sodium channel) on chromosome 2
• FHM type 4 is diagnosed if no mutation currently known to cause FHM can be identified

Inheritance of FHM is autosomal dominant, however not everyone with the inherited mutation for FHM will have symptoms (reduced penetrance)

• FHM commonly begins during childhood or adolescence
• diagnosis of FHM requires that at least one first- or second-degree relative has also been diagnosed with hemiplegic migraine. Tests such as a CT scan or MRI of the brain, CSF, and EEG may be needed to rule out other potential causes of headache and neurological symptoms
• genetic testing may confirm the subtype of FHM in a family.
  

Familial hemiplegic migraine very often presents with brainstem symptoms in addition to the typical aura symptoms, and that headache almost always occurs

• rarely, during FHM attacks, disturbances of consciousness (sometimes including coma), confusion, fever and cerebrospinal fluid (CSF) pleocytosis can occur
• Familial hemiplegic migraine may be mistaken for epilepsy
• FHM attacks can be triggered by (mild) head trauma
• in approximately 50% of FHM families, chronic progressive cerebellar ataxia occurs independently of the migraine attacks migraine

Reference:

• Ashina M. Migraine. N Engl J Med 2020;383:1866-76. DOI: 10.1056/NEJMra1915327
• Headache Classification Committee of the International Headache Society (IHS). The international classification of headache disorders, 3rd edition. Cephalalgia 2018; 38: 1-211
• NICE (September 2012). Headaches - Diagnosis and management of headaches in young people and adults