What is familial hemiplegic migraine (FHM)?

Updated: Aug 15, 2019
  • Author: William C Robertson, Jr, MD; Chief Editor: Amy Kao, MD  more...
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Familial hemiplegic migraine (FHM) is an autosomal dominant form of migraine with aura; at least one first-degree or second-degree relative has migraine with aura involving weakness. Episodes are marked by a prolonged hemiplegia accompanied by numbness, aphasia, and confusion. The hemiplegia may precede, accompany, or follow the headache, and symptoms may last for hours or for even as long as a week. The headache is usually contralateral to the hemiparesis. Some FHM attacks are associated with cerebellar ataxia.

Other more severe symptoms of FHM may include coma, fever, and meningismus; progressive ataxia, nystagmus, gait unsteadiness, limb incoordination, and dysarthria.

Genetic abnormalities have been identified; CACNA1A gene mutations (coding for calcium channel) on chromosome 19 in FHM1; mutations in the ATP1A2 gene (coding for a K/Na-ATPase) on chromosome 1 in FHM2; and mutations in the SCN1A gene (coding for a sodium channel) on chromosome 2 in FHM3. [1]

Consider structural lesions, vasculitis, cerebral hemorrhage, brain tumor, mitochondrial myopathy, encephalopathy, and lactic acidosis in the differential diagnosis. If hemiparesis is always on the same side, consider a vascular abnormality.

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