Erythromelalgia is a rare condition classically presenting with intermittent symptoms of severe paroxysmal burning sensation, erythema, and warmth of the skin, usually involving the extremities, lower more often than upper. It has also been reported to involve the face, ears, and genital area.

Erythromelalgia may be primary or secondary, with primary erythromelalgia (PE) further separated by some into a primary inherited form and an idiopathic group. Others consider only the inherited form as PE. This primary inherited form is due to an autosomal dominant mutation in the SCN9A gene on chromosome 2q that encodes for Nav 1.7 (voltage-gated sodium channels present in small nociceptive neurons). By contrast, secondary erythromelalgia can be associated with a multitude of underlying conditions. These include myeloproliferative disorders with thrombocythemia, in addition to vascular, connective tissue, neurological, and musculoskeletal conditions. Some drug reactions have been reported to trigger erythromelalgia, as have poisonings and intoxications.

Poisoning from ingestion of the mushroom Paralepistopsis (formerly Clitocybe) acromelalga causes a self-limited form of erythromelalgia. Onset is within 2-3 days of ingestion, and symptoms usually resolve in 1-2 weeks but may persist for months.

Incidence estimates have ranged from 0.3 to 1.3/100 000 for all forms of erythromelalgia, and these are considered low due to underdiagnosis. Some studies suggest a female predominance of up to 2-3:1, and there does not appear to be a racial / ethnic predilection.