Erythromelalgia

Erythromelalgia is a condition characterized by episodes of pain, redness, and swelling in various parts of the body, particularly the hands and feet. These episodes are usually triggered by increased body temperature, which may be caused by exercise, wearing socks or tight shoes, or entering a warm room. Ingesting alcohol or spicy foods may also trigger an episode. As affected individuals get older and the disease progresses, the hands and feet may be constantly red, and the affected areas can extend to the upper legs and face.

The pain associated with erythromelalgia can be so debilitating that it impedes everyday activities such as wearing shoes and walking. It may also prevent an affected person from regularly going to school or work.

The prevalence of erythromelalgia is unknown.

Mutations in the SCN9A gene cause some cases of erythromelalgia. The SCN9A gene provides instructions for making one part of a sodium channel called NaV1.7. Sodium channels transport positively charged sodium atoms (sodium ions) into cells and play a key role in a cell's ability to generate and transmit electrical signals. The NaV1.7 sodium channels are found in specific nerve cells called nociceptors, located just outside the spinal cord, which are involved in transmitting pain signals.

The SCN9A gene mutations that cause erythromelalgia result in a NaV1.7 sodium channel that opens more easily than usual and stays open longer than normal, increasing the flow of sodium ions into nociceptors. This increase in sodium ions enhances transmission of pain signals, leading to the signs and symptoms of erythromelalgia. It is unknown why the pain episodes associated with erythromelalgia mainly occur in the hands and feet.

An estimated 15 percent of cases of erythromelalgia are caused by mutations in the SCN9A gene. Some cases are thought to have a non-genetic cause or may be caused by mutations in one or more as-yet unidentified genes.

Read more about the SCN9A gene.

Some cases of erythromelalgia are inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some of these instances, an affected person inherits the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.