Erythromelalgia

Erythromelalgia, also known as Mitchell's disease (after Silas Weir Mitchell), acromelalgia, red neuralgia, or erythermalgia, is a rare neurovascular peripheral pain disorder in which blood vessels, usually in the lower extremities (or hands), are episodically blocked (frequently on and off daily), then become hyperemic and inflamed. There is severe burning pain (in the small fiber sensory nerves) and skin redness. The attacks are periodic and are commonly triggered by heat, pressure, mild activity, exertion, insomnia or stress. Erythromelalgia may occur either as a primary or secondary disorder (i.e. a disorder in and of itself or a symptom of another condition). Secondary erythromelalgia can result from small fiber peripheral neuropathy of any cause, essential thrombocytosis (erythromelalgia can also develop in the presence of normal platelet counts in patients with myeloproliferative disorder), hypercholesterolemia, mushroom or mercury poisoning, and some autoimmune disorders.. Primary erythromelalgia is caused by mutation of the voltage-gated sodium channel α-subunit gene SCN9A.

In 2004 Erythromelalgia became the first human disorder in which it has been possible to associate an ion channel mutation with chronic neuropathic pain; this became possible when a Yale neurologist spotted a Beijing geneticists team paper in the Journal of Medical Genetics titled "Mutations in SCN9A, Encoding a Sodium Channel Alpha Subunit, in Patients With Primary Erythromelalgia"; a connection was made that this sodium channel mutation was expressed primarily in peripheral pain sensing neurons. Conversely, in December 2006 a University of Cambridge team reported an SCN9A mutation that created a complete "lack of" pain sensation in the family of a Pakistan street performer. He felt no pain, walked on hot coals and stabbed himself to entertain crowds.