Familial hemiplegic migraine: causes, symptoms, diagnosis, and management

A hereditary, rare migraine subtype marked by temporary one-sided weakness and neurologic aura. Covers genetics, clinical features, diagnosis, treatment options, and distinctions from stroke.

Overview

Familial hemiplegic migraine (FHM) is an uncommon inherited form of migraine in which attacks include temporary weakness or paralysis on one side of the body (hemiplegia) together with the typical sensory or visual disturbances of a migraine migraine and aura. Attacks vary in severity and duration; most episodes are reversible but may be severe and debilitating during the acute phase. The disorder is notable for a clear family history of similar episodes in many affected families.

Genetics and mechanism

FHM is usually inherited in an autosomal dominant pattern. Several genes have been linked to different FHM subtypes; these genes encode ion channels or ion transport proteins that influence neuronal excitability. Altered ion handling is thought to lower the threshold for spreading cortical depression and other electrical disturbances that produce aura and transient motor weakness. Genetic testing can identify known pathogenic variants in many but not all cases.

Clinical features

Typical attacks combine migraine headache and transient focal neurological signs. Common features include:

Progressive visual, sensory or speech aura preceding or accompanying headache;
Unilateral weakness or paralysis affecting the arm and/or leg (hemiplegia) that can last minutes to days;
Associated symptoms such as nausea, photophobia, confusion, or reduced consciousness in severe attacks;
Onset often in childhood or adolescence, with variable frequency of episodes.

Diagnosis and management

Diagnosis rests on clinical history, family history, and exclusion of other causes of sudden focal deficits—most importantly stroke. Neuroimaging and other acute investigations are used when the presentation is atypical or severe. Genetic testing is available to confirm known FHM genes in many families. Management is individualized and focuses on symptom relief during attacks and prevention of future episodes. Acute care may require hospital evaluation to rule out other emergencies. Preventive strategies can include lifestyle measures and medications chosen by a physician experienced with migraine and channelopathies; some standard migraine therapies are used cautiously. Genetic counselling is recommended for affected families.

Prognosis and important distinctions

Most patients recover neurological function between attacks, though rare cases have prolonged deficits. FHM is distinct from more common migraine with aura because of the pronounced motor weakness and its inherited pattern, and it must be differentiated from stroke and other episodic neurological disorders. Recognizing family history and typical aura progression helps clinicians reach the correct diagnosis and avoid unnecessary or harmful treatments.