What is erythema nodosum?

Definition

Erythema nodosum (EN) is an
inflammation of subcutaneous fat tissue characterized by nodules beneath the skin. EN is considered a nonspecific immune-related skin reaction with an incidence of 1 to 5 per 100,000 persons each year. EN is more common in women than in men. The predominant age of those infected is between fifteen and forty years.

Causes

Although the cause of about 50 percent of EN cases is unknown, the most common
cause is streptococcal pharyngitis (up to 44 percent in adults
and 48 percent in children). The most common bacterial agent for streptococcal
pharyngitis in children and adolescents is
Streptococcus pyogenes (group A Streptococcus,
or GAS). Other causes of EN include gastrointestinal disorders (Crohn’s
disease, ulcerative colitis, bacterial gastroenteritis);
diseases with large lymph nodes (hilar adenopathy) in the middle part of the chest
(sarcoidosis, tuberculosis); diseases caused by
various infectious agents (other bacteria, syphilis, cat
scratch fever, leprosy); fungi (histoplasmosis, coccidiomycosis,
blastomycosis); viruses (human immunodeficiency
virus, hepatitis B, cytomegalovirus); protozoa
(giardiasis, toxoplasmosis, amebiasis);
medications (sulfonamides, amoxicillin, oral contraceptives); rheumatologic,
inflammatory, and autoimmune disorders (systemic lupus erythematosus,
rheumatoid
arthritis, scleroderma); cancers (leukemia,
lymphoma, colon cancer); and pregnancy.

Risk Factors

Persons with conditions noted in the foregoing section are at risk for developing EN.

Symptoms

EN starts as a red, hot, flat, firm, palpable, and painful nodule or lump, most
commonly in the shins, but it may affect other parts of the body (such as the
forearms, arms, trunk, thighs, and ankles). The nodule is usually one inch in
diameter but can be up to four inches in diameter. The nodules change color from
purplish (in days) to brownish patches (in weeks). Other symptoms may occur one to
three weeks before the appearance of the nodule, These symptoms include fever,
malaise, and joint aches, and inflammation or swelling of the affected areas.

Screening and Diagnosis

A physician will perform a thorough medical history evaluation and a physical examination, considering the wide spectrum of conditions that can cause EN. Diagnosis is based on the clinical features of EN. To establish the most probable cause, studies may include blood tests (complete blood count with differential, erythrocyte sedimentation rate, C-reactive protein, liver enzymes and products, and basic metabolic panel), determining streptococcal infection (antistreptolysin-O level, throat culture, and polymerase chain reaction), chest radiograph to evaluate hilar adenopathy, tuberculin skin test for tuberculosis, and stool cultures to evaluate gastrointestinal causes. Excisional biopsy of the skin lesion may be needed, if EN diagnosis is uncertain.

Treatment and Therapy

EN usually resolves, and treatment focuses on managing the underlying cause.
Pain relief can be provided with nonsteroidal anti-inflammatory drugs
(such as naproxen or ibuprofen). A solution of potassium iodide taken for one
month is another treatment and is most effective when taken during the early
manifestation of EN. Thyroid function should be monitored if potassium iodide will
be used long-term because it can cause hyperthyroidism. If infection and
malignancy have been ruled out, oral steroid is another therapeutic option.

Prevention and Outcomes

There is no vaccination or medication that can prevent EN. One should practice basic hygiene measures that help prevent infections. Recommended cancer screenings should be followed, such as colonoscopy for colon cancer screening, based on clinical guidelines. Finally, one should adhere to medication regimens for the causative diseases.

Bibliography

Ferri, Fred F. “Erythema Nodosum.” In Ferri’s Clinical Advisor 2011: Instant Diagnosis and Treatment, edited by Fred F. Ferri. Philadelphia: Mosby/Elsevier, 2011.

Requena, Luis, and Evaristo Sanchez Yus. “Erythema Nodosum.” Dermatologic Clinics 26 (2008): 425-438.

Schwartz, Robert A., and Stephen J. Nervi. “Erythema Nodosum: A Sign of Systemic Disease.” American Family Physician 75 (2007): 695-700.