Erythema nodosum

Erythema nodosum is an inflammation of the fatty tissue located under the skin (panniculitis) that manifests through the appearance of painful nodules, generally on the front of the legs.

It is not a disease in itself, but an inflammatory reaction that can appear as a consequence of different diseases, infections, medications or physiological situations such as pregnancy. In most cases it evolves favourably and disappears without leaving scars.

In approximately half of the patients no concrete cause is identified (idiopathic erythema nodosum). When there is a cause, the most frequent are:

Infections. Streptococcal pharyngitis, tuberculosis, Yersinia, Mycoplasma and some viral infections.

Inflammatory diseases. Sarcoidosis, inflammatory bowel disease (Crohn's disease and ulcerative colitis) and Behçet's disease.

Medications. Some antibiotics, oral contraceptives, sulfonamides and other drugs less frequently.

Other situations. Pregnancy, some autoimmune diseases and certain neoplasms, infrequently.

The main symptom is the appearance of painful inflammatory nodules. The usual characteristics are reddish nodules, pain on pressure, local heat, size between 1 and 5 centimetres and a generally symmetrical distribution.

The most frequent location is the front of the legs and, less frequently, they can appear on the thighs and forearms.

In addition, fever, tiredness, general malaise, joint pain and swelling of the ankles may be associated.

As they evolve, the nodules change colour, similarly to a bruise, going from red to violaceous and later to yellowish before disappearing.

The diagnosis is based on the clinical history, the physical examination and the search for the triggering cause. The doctor will ask about recent infections, usual medication, travel, previous diseases and respiratory or digestive symptoms.

What tests may be necessary? Depending on each patient, blood tests, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), blood count, culture or rapid test for streptococcus, chest X-ray (especially to rule out sarcoidosis or tuberculosis), tuberculin test or IGRA when indicated and digestive studies if there are intestinal symptoms may be requested.

Is a biopsy necessary? Usually not. It is only performed when there are diagnostic doubts or atypical lesions.

Treatment consists mainly of treating the cause when it is identified.

General measures. Relative rest, elevating the legs, compression stockings when indicated and avoiding intense efforts during the acute phase.

Symptomatic treatment. To relieve the pain, non-steroidal anti-inflammatory drugs (NSAIDs), if they are not contraindicated, and analgesics can be used.

Treatment of the underlying disease. When there is an identifiable cause, the treatment must be directed at that disease. For example, antibiotics in certain bacterial infections, treatment of sarcoidosis, control of inflammatory bowel disease or discontinuation of the responsible medication when possible. In severe or persistent cases, other immunomodulatory treatments can be considered under medical supervision.

Rest during flare-ups, avoid standing for many hours, maintain good hydration, follow the treatment indicated by your doctor, do not self-medicate with antibiotics and consult if new symptoms appear.

You should consult if painful nodules appear on the legs, if you have persistent fever, if you present significant joint pain, if the nodules increase rapidly in size, if the symptoms last more than six weeks or if you repeat episodes frequently.

• Myth: Erythema nodosum is a skin infection. Fact: No. It is an inflammation of the subcutaneous fatty tissue and, although it can be triggered by an infection, the lesions are not infected.
• Myth: It is contagious. Fact: No.
• Myth: It always means a serious disease. Fact: No. In many patients no important cause is found and the evolution is benign.
• Myth: The nodules must be drained. Fact: No. They do not contain pus and must not be opened.
• Myth: It always leaves scars. Fact: It usually disappears completely without leaving scars.

• Erythema nodosum is an inflammation of the fatty tissue under the skin.
• It manifests through painful nodules, especially on the front of the legs.
• It is not contagious.
• It can be related to infections, inflammatory diseases, medications or pregnancy.
• Treatment consists of relieving the symptoms and treating the cause when it is identified.
• The evolution is usually favourable and most patients do not present sequelae.