Erythema Nodosum – A Complete Patient‑Friendly Guide
Overview
Erythema nodosum (EN) is an inflammatory condition that produces tender, red‑purple nodules most commonly on the shins. It is not a primary disease; rather, it is a reaction pattern that can be triggered by infections, medications, systemic illnesses, or pregnancy.
- Typical age: 20–40 years, but can occur at any age.
- Gender: Women are affected about twice as often as men, partly because many triggers (e.g., pregnancy, oral contraceptives, certain infections) are more common in females.
- Prevalence: Estimated at 1–5 cases per 100,000 population per year in the United States and Europe. In some regions with high rates of streptococcal infection or sarcoidosis, incidence can be higher.
Although EN is usually self‑limited, the nodules can be painful and may be a clue to an underlying systemic problem that requires treatment.
Symptoms
The presentation can vary, but the classic symptom complex includes:
Skin findings
- Red‑purple nodules: 1–5 cm, raised, firm to the touch, most often located on the anterior lower legs.
- Bilaterality: Lesions appear on both legs in ~80 % of cases.
- Evolution: Nodules may soften, change color to bruise‑like (blue‑purple), then fade over 2–6 weeks, often leaving a faint brownish discoloration.
Pain & discomfort
- Sharp or aching pain that intensifies with walking or standing.
- Reduced ability to wear tight shoes or engage in prolonged activity.
Systemic symptoms
- Low‑grade fever (up to 38 °C/100.4 °F) in 25 % of patients.
- Generalized fatigue and malaise.
- Arthralgia (joint pain) especially of the ankles, knees, and wrists.
- Occasional mild pleuritic chest pain if associated with sarcoidosis or other lung disease.
Other possible findings
- Enlarged lymph nodes (especially cervical) when infection is the trigger.
- Abdominal pain or diarrhea if the cause is a gastrointestinal infection (e.g., Yersinia).
Causes and Risk Factors
EN is a hypersensitivity reaction in the subcutaneous fat (panniculitis). Over 70 % of cases have an identifiable trigger.
Infectious triggers
- Streptococcal pharyngitis – most common bacterial cause, especially in children and adolescents (≈30 %).
- Yersinia enterocolitica – associated with abdominal pain and diarrhea.
- Mycobacterium tuberculosis – especially in endemic areas.
- Viral infections: Epstein‑Barr virus (EBV), hepatitis B & C, HIV, and SARS‑CoV‑2 have been reported.
Systemic diseases
- Sarcoidosis – the second most common non‑infectious cause in adults.
- Inflammatory bowel disease (Crohn’s disease, ulcerative colitis).
- Behçet’s disease and systemic lupus erythematosus.
Medications
- Oral contraceptives (estrogen‑containing).
- Sulfonamides, penicillins, and cephalosporins.
- Non‑steroidal anti‑inflammatory drugs (NSAIDs) – paradoxically, can both trigger and treat EN.
- Vaccines (rarely, e.g., BCG, hepatitis B).
Other risk factors
- Pregnancy – hormonal changes may predispose.
- Obesity – increased subcutaneous fat may amplify the inflammatory response.
- Recent upper respiratory infection – even if the pathogen isn’t identified.
Diagnosis
Diagnosis is primarily clinical, supported by history, physical examination, and targeted investigations to find the underlying cause.
Step‑by‑step approach
- History and physical exam: Note onset, distribution of nodules, recent infections, medication changes, systemic symptoms.
- Laboratory tests:
- Complete blood count (CBC) – often shows mild leukocytosis or anemia.
- Erythrocyte sedimentation rate (ESR) and C‑reactive protein (CRP) – usually elevated, reflecting inflammation.
- Throat culture or rapid streptococcal antigen test if recent sore throat.
- Serologies for Yersinia, TB (Quantiferon), hepatitis B/C, HIV, EBV as indicated.
- Pregnancy test in women of child‑bearing age.
- Imaging: Chest X‑ray to assess for sarcoidosis or TB; abdominal ultrasound/CT if gastrointestinal infection suspected.
- Skin biopsy (rarely needed): A 4‑mm punch from a fresh nodule shows a septal panniculitis without vasculitis. Biopsy is reserved for atypical presentations or when malignancy is a concern.
According to the American Academy of Dermatology, a thorough work‑up finds a trigger in >80 % of adult cases when systematic testing is performed (source: AAD).
Treatment Options
Therapy has two goals: (1) relieve symptoms and (2) treat the underlying cause.
Addressing the underlying trigger
- Streptococcal infection: Penicillin V 250 mg three times daily for 10 days (or a single dose of intramuscular benzathine penicillin). Alternative: amoxicillin.
- Yersinia or other bacterial infections: Appropriate antibiotics (e.g., doxycycline or fluoroquinolones if resistant).
- Tuberculosis: Standard multi‑drug anti‑TB regimen.
- Sarcoidosis: Usually managed with systemic steroids or steroid‑sparing agents (methotrexate, azathioprine).
- Medication‑induced EN: Discontinue the offending drug under physician guidance.
Symptomatic management
- Non‑steroidal anti‑inflammatory drugs (NSAIDs): Ibuprofen 400–600 mg every 6–8 h or naproxen 250 mg twice daily. Helps with pain and inflammation.
- Colchicine: 0.6 mg 1–2 times daily; useful for patients who cannot tolerate NSAIDs.
- Systemic corticosteroids: Prednisone 20–40 mg daily for 1–2 weeks, then taper. Reserved for severe or rapidly progressive disease, or when the trigger cannot be rapidly eliminated.
- Potassium iodide: 5–10 drops of saturated solution three times daily; historically used, but less common due to side‑effects.
Supportive care
- Compression stockings or elastic bandages to reduce swelling.
- Elevation of legs above heart level for 15–20 minutes several times a day.
- Cool compresses (10‑15 min) to soothe itching.
- Topical corticosteroid creams (e.g., 1 % hydrocortisone) for localized itching.
When to involve specialists
- Dermatology – for atypical lesions or uncertain diagnosis.
- Pulmonology – if sarcoidosis or TB is suspected.
- Rheumatology – when EN is part of a systemic autoimmune process.
Living with Erythema Nodosum
Most patients recover within 3–6 weeks, but the experience can be uncomfortable. Practical tips:
- Activity modification: Walk short distances; avoid prolonged standing or high‑impact exercise until pain subsides.
- Footwear: Choose soft, supportive shoes with cushioned soles; avoid high heels or tight boots.
- Skin care: Keep lesions clean; mild soap and lukewarm water. Pat dry—do not rub.
- Diet: A balanced diet supports immune health. Some clinicians recommend a low‑salt diet to reduce edema.
- Stress management: Stress can modulate immune response; consider relaxation techniques (deep breathing, yoga).
- Follow‑up: Schedule appointments every 2–4 weeks until lesions resolve and the trigger is controlled.
Prevention
Because EN is often secondary, prevention focuses on reducing exposure to known triggers.
- Prompt treatment of streptococcal throat infections; complete the full antibiotic course.
- Practice good hand hygiene and food safety to avoid gastrointestinal infections.
- Review medications with your provider before starting new drugs, especially sulfonamides or oral contraceptives.
- Maintain a healthy weight to lessen subcutaneous fat inflammation.
- During pregnancy, discuss any skin changes with obstetric care; early identification allows safe management.
Complications
Although EN is rarely life‑threatening, complications can arise if the underlying disease is not addressed.
- Chronic or recurrent EN: Seen in sarcoidosis, inflammatory bowel disease, or ongoing infection.
- Persistent hyperpigmentation or scar-like changes at lesion sites.
- Venous thromboembolism: Very rare, but inflammatory panniculitis can promote a hypercoagulable state.
- Underlying systemic disease progression: For example, untreated sarcoidosis may affect lungs, heart, or eyes.
When to Seek Emergency Care
Call 911 or go to the nearest emergency department immediately if you experience any of the following:
- Sudden, severe shortness of breath or chest pain that worsens with breathing.
- High fever (> 39 °C / 102 °F) accompanied by confusion, stiff neck, or severe headache.
- Rapid swelling of the legs with redness that spreads quickly (possible cellulitis or deep vein thrombosis).
- Severe abdominal pain with vomiting, especially if you have a known infection trigger.
- Signs of an allergic reaction after starting a new medication (hives, swelling of lips/tongue, difficulty breathing).
These symptoms may indicate a serious infection, pulmonary embolism, or an acute systemic reaction requiring urgent treatment.
**References**
- Mayo Clinic. “Erythema Nodosum.” https://www.mayoclinic.org. Accessed June 2024.
- American College of Rheumatology. “Erythema Nodosum.” ACR Clinical Guidelines, 2023.
- CDC. “Streptococcal Disease.” https://www.cdc.gov. Updated 2022.
- World Health Organization. “Tuberculosis Factsheet.” WHO, 2022.
- Cleveland Clinic. “Sarcoidosis and Skin Involvement.” https://my.clevelandclinic.org. 2023.
- J. W. H. Kwon et al., “Erythema Nodosum: A Review of Clinical Features and Management,” *Dermatology* 2021; 237(4): 361‑369.