Hemiplegic migraine

Hemiplegic migraines are an uncommon type of migraine with aura wherein patients present with usually reversible motor weakness, typically unilateral. They can be challenging to distinguish from seizure with Todd paresis or ischemic stroke, even with the benefit of MRI ¹.

Epidemiology

Compared to migraines, which are common and experienced by 15-20% of the population, hemiplegic migraines are rare, with an overall prevalence of only 0.01% ¹¹. Most patients present with the first event before the age of 20 years of age, typically during adolescence ^1,10. As individuals age, the frequency and severity of attacks tend to diminish ¹⁰. Women are affected 2.5-4.3 times more frequently than men ¹¹.

Hemiplegic migraines can either be sporadic or familial. Family history is generally defined as having one or more first or second-degree relatives with the condition ^1,10.

Clinical presentation

Patients usually present first with aura, which in the setting of hemiplegic migraine includes unilateral motor weakness, followed by headache, although sometimes the headache may be concurrent with aura or even precede the aura ^1-3,10. Numerous other signs and symptoms have been reported, including confusion, neuropsychiatric features, visual hallucinations, visual field defects, photophobia, and aphasia ^1,2. In severe cases, patients may have decreased levels of consciousness and even coma ².

Fever is also common and CSF analysis may demonstrate a pleocytosis ^1,2.

In approximately half of families with familial hemiplegic migraine, a chronic progressive cerebellar ataxia is present ³.

Pathology

The pathophysiology of migraine remains to be fully elucidated and it is unclear whether the vascular changes observed are the primary cause (aura representing vasoconstriction and headache resulting form subsequent vasodulation) or secondary to waves of abnormal neuronal activity ¹².

Familial hemiplegic migraine is generally inherited as an autosomal dominant trait with approximately 80% penetrance ^1-3,10. Mutations in a number of genes have been implicated although it is believed others are yet to be identified ³.

• FHM1: CACNA1A gene (chromosome 19)

• FHM2: ATP1A2 (chromosome 1)

• FHM3: SCN1A (chromosome 2)

• familial hemiplegic migraine, other loci

These subtypes cannot be reliably distinguished clinically and require genetic testing ⁷.

Hemiplegic migraines can also occur sporadically (in the absence of family history) but are only uncommonly the result of mutations in the aforementioned known FHM genes. The underlying cause in sporadic cases remains to be fully understood ¹⁰.

Radiographic features

MRI

The MRI findings vary between individuals and seem to also depend on the underlying genetic abnormality ¹.

• T1

  • usually normal

  • gyral swelling may be visible, better seen on T2

• T1 C+

  • usually normal

  • some gyral enhancement may be seen ⁸

• T2

  • gyral swelling and hyperintensity; most common in FHM1

• MRA

  • often normal ⁴

  • reduced or increased caliber of arteries may be seen in a minority of individuals ⁴

• perfusion ^4-6

  • perfusion abnormalities in the majority of patients

  • severity and pattern may vary depending on the timing of the scan relative to symptoms

    • aura: hypoperfusion and vasoconstriction ^5,6

    • headache: hyperperfusion and vasodilation ^5,6

  • defect is almost never limited to single vascular territories

  • which map is most affected is variably reported and depends on individual patients, how the maps are generated, how they are interpreted (visual vs quantification) and the phase of attack ^4,5

• SWI

  • cortical vein prominence matching areas of abnormal perfusion ⁶

  • best seen on minIP

  • likely be due to changes in oxygenation of hemoglobin with the veins draining abnormally perfused brain (increase deoxyhemoglobin), rather than vasodilation ⁶

Treatment and prognosis

Although most cases spontaneously resolve within 72 hours with supportive therapies, sometimes it may take a number of weeks for full recovery ^7,10. Rarely, particularly in FHM1, recovery is incomplete and even more rarely severe attacks can even result in death ¹⁰.

Acute treatment is typically with non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen ⁷. If headaches do not abate, triptans can be administered, although this is controversial and even historically thought to be contraindicated ^7,10.

Often, however, before the diagnosis is evident, patients may receive antibiotics, antivirals, antiseizure medications, corticosteroids, intravenous thrombolysis or intravenous immunoglobulin to cover potential differential diagnoses (see below) ¹.

As with non-hemiplegic migraine, preventative therapies are also important to reduce the frequency of attacks. These include a wide variety of agents, including verapamil, flunarizine and acetazolamide, as well as advanced therapies such as monoclonal antibodies targeting the calcitonin gene-related peptide (CGRP) ^9,10.

Differential diagnosis

One of the primary challenges in hemiplegic migraine is that the differential diagnosis includes entities with dire consequences and drastically different management ^1,10.

• migraine with unilateral motor symptoms (MUMS)

• epilepsy with Todd paralysis

• ischemic stroke

• meningoencephalitis (infective or autoimmune)

• CADASIL

• HaNDL

• alternating hemiplegia of childhood