Erythromelalgia (EM) is a rare neurovascular pain disorder that can cause redness and pain in all parts of the body, but most frequently the extremities, such as the hands and feet. It is characterized by intense burning pain, severe redness (erythema), and increased skin temperature that may be episodic or almost continuous in nature. The specific underlying cause of EM remains unknown.
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.