English: Erythromelalgia (EM), with its painful, burning erythema, is in most cases (some 80–90%) due to an underlying neuropathy that causes the blood vessels to contract and dilate in an abnormal way as well as making the blood flow bypass the capillaries. Even though the erythema is caused by an excessive flush of blood in the affected extremity, the tissues paradoxally suffer from a lack of oxygen and nutrients since the blood does not reach the capillaries. Instead it flows directly from the small arteries (arterioles) through arteriovenous anastomoses directly to the small veins (venules). (Such anastomoses are vessels that directly interconnect arteries and veins, acting as shunts to bypass the capillary beds.) The signals from the ischemic tissues cause the central nervous system to increase the blood flow even further, thus increasing the vicious circle. In the majority of people with EM, the areas affected are the soles of the feet. Inbetween EM episodes, which are often triggered by heat, the skin tends to be cold and cyanotic. The photo shows an EM episode in the foot of a male with a small fiber neuropathy. The EM here affects the sole and the toes and was in this case triggered by exposure to warm water.