Erythromelalgia or erythermalgia is a rare disorder with typical complaints of burning pain, red discoloration and swelling of feet and sometimes hands, often provoked by warm temperature or exercise. The disorder has a variety of underlying causes, such as an increased number of blood platelets.

The term erythermalgia usually is used for the inheritable variant of the disease. Inherited erythermalgia is caused by a mutation in the DNA for a certain sodium channel, the SCN9A gene. This sodium channel, Nav1.7, is mainly present in the small nerve fibres. A mutation in this gene causes hyperactivity of the channel, ultimately leading to pain signals to the brain without physical pain stimuli being present.

A subset of patients with small fibre neuropathy has complaints compatible with erythermalgia, whereas some patients with erythermalgia also have small fibre neuropathy. Therefore, both disorders probably are part of the same spectrum.