Erythema nodosum
Erythema nodosum (EN) is a condition characterized by inflammation of the subcutaneous fat tissue, resulting in painful red nodules typically found on the shins. It is considered a nonspecific immune-related skin reaction, with an incidence of 1 to 5 per 100,000 individuals annually and is more prevalent in women aged 25 to 40. The exact cause of EN is often unknown, but it is frequently associated with streptococcal throat infections, gastrointestinal disorders, certain infectious diseases, and various medications.
Symptoms of EN may include fever, malaise, and joint aches that can precede the appearance of the nodules. Diagnosis is primarily clinical but may involve blood tests and imaging to rule out underlying conditions. Treatment usually focuses on alleviating pain with nonsteroidal anti-inflammatory drugs and addressing any underlying causes, as EN often resolves on its own. While there is no specific prevention for EN, practicing good hygiene and following medical guidance for associated conditions may reduce the risk. Overall, EN is a manageable condition, but its varied causes highlight the importance of a thorough medical evaluation.
Erythema nodosum
- ANATOMY OR SYSTEM AFFECTED: Skin, tissue
Definition
Erythema nodosum (EN) is an inflammation of subcutaneous fat tissue characterized by nodules beneath the skin. EN is 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 twenty-five 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, coccidioidomycosis, 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. Other conditions that may increase an individual’s risk of developing EN include psittacosis, hormonal changes, and mononucleosis. Some medications are also linked to EN, including antibiotics containing penicillin and sulfur, bromides, iodides, and birth control pills.
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. An 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
"Erythema Nodosum." Icahn School of Medicine at Mount Sinai, www.mountsinai.org/health-library/diseases-conditions/erythema-nodosum. Accessed 20 Oct. 2024.
"Erythema Nodosum." Johns Hopkins University, www.hopkinsmedicine.org/health/conditions-and-diseases/erythema-nodosum. Accessed 20 Oct. 2024.
"Erythema Nodosum." WebMD, 28 Nov. 2023, www.webmd.com/skin-problems-and-treatments/erythema-nodosum. Accessed 20 Oct. 2024.
Ferri, Fred F. “Erythema Nodosum.” Ferri’s Clinical Advisor 2011: Instant Diagnosis and Treatment, edited by Fred F. Ferri, Mosby/Elsevier, 2011.
Requena, Luis, and Evaristo Sanchez Yus. “Erythema Nodosum.” Dermatologic Clinics, vol. 26, 2008, pp. 425-38, doi:10.1016/j.det.2008.05.014. Accessed 20 Oct. 2024.
Schwartz, Robert A., and Stephen J. Nervi. “Erythema Nodosum: A Sign of Systemic Disease.” American Family Physician, vol. 75, no. 5, 2007, pp. 695–700, www.anwhospitalist.com/wp-content/uploads/2021/07/afp-EN.pdf. Accessed 20 Oct. 2024.