Pathophysiology
The rash of scarlet fever, which is what differentiates this disease from an isolated group A strep pharyngitis (or strep throat), is caused by specific strains of group A streptococcus which produce a pyrogenic exotoxin, mainly responsible for the skin manifestation of the infection. These toxin-producing strains cause scarlet fever in people who do not already have antitoxin antibodies. Streptococcal pyrogenic exotoxins A, B, and C (speA, speB, and speC) have been identified. The pyrogenic exotoxins are also called erythrogenic toxins and cause the erythematous rash of scarlet fever. The strains of group A streptococcus that cause scarlet fever need specific bacteriophages for there to be pyrogenic exotoxin production. Specifically, bacteriophage T12 is responsible for the production of speA. Streptococcal Pyrogenic Exotoxin A, speA, is the one which is most commonly associated with cases of scarlet fever which are complicated by the immune-mediated sequelae acute rheumatic fever and post-streptococcal glomerulonephritis.These toxins are also known as "superantigens" because they are able to cause an extensive immune response within the body through activation of some of the main cells responsible for the persons immune system. The body responds to these toxins by making antibodies to those specific toxins. However, those antibodies do not completely protect the person from future group A streptococcal infections, because there are 12 different pyrogenic exotoxins possible. Microbiology
The disease is caused by secretion of pyrogenic exotoxins by the infecting Streptococcus bacteria. Streptococcal pyrogenic exotoxin A (speA) is probably the best studied of these toxins.
Screening
Prenatal screening is not typically done for FHM, however it may be performed if requested. As penetrance is high, individuals found to carry mutations should be expected to develop signs of FHM at some point in life. Management
See the equivalent section in the main migraine article. People with FHM are encouraged to avoid activities that may trigger their attacks. Minor head trauma is a common attack precipitant, so FHM sufferers should avoid contact sports. Acetazolamide or standard drugs are often used to treat attacks, though those leading to vasoconstriction should be avoided due to the risk of stroke. Epidemiology
Migraine itself is a very common disorder, occurring in 15–20% of the population. Hemiplegic migraine, be it familial or spontaneous, is less prevalent, 0.01% prevalence according to one report. Women are three times more likely to be affected than males. References


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