Erythema Nodosum: A Complete Patient‑Friendly Guide

Overview

Erythema nodosum (EN) is an inflammatory condition that causes tender, red‑violet nodules—usually on the shins. It is not a primary disease but a reaction to another underlying problem such as infection, medication, or systemic illness.

• Typical age: 20–40 years, though it can occur at any age.
• Gender: Slight female predominance (≈60 % of cases).
• Prevalence: Estimated 1–5 cases per 100,000 people per year in the United States; higher in regions where certain infections (e.g., streptococcal pharyngitis, tuberculosis) are common [1][2].

Most episodes are self‑limited, resolving within 3–6 weeks, but the condition can be recurrent or chronic when the trigger persists.

Symptoms

The signs and symptoms can vary, but the classic presentation includes:

• Skin nodules: Firm, raised, warm, red‑purple plaques 1–5 cm in diameter, usually on the anterior lower legs. They may become bruised or yellow‑ish as they heal.
• Pain or tenderness: Discomfort can be mild to severe, worsened by walking or standing.
• Swelling: Often accompanies the nodules, giving the lower leg a “cobblestone” appearance.
• Fever: Low‑grade fever (≤38 °C/100.4 °F) in 30‑40 % of patients, especially when infection is the trigger.
• Arthralgia or arthritis: Joint pain, most commonly in the ankles, knees, or wrists. Inflammatory arthritis occurs in ~10 % of cases.
• Fatigue, malaise, and weight loss: General systemic symptoms that often reflect the underlying cause.
• Recurrence: New nodules may appear as old lesions fade, sometimes in a “wave” pattern.

Causes and Risk Factors

EN is a hypersensitivity reaction to a wide variety of antigens. Common categories include:

Infections (≈50 % of cases)

• Streptococcal throat infection (Group A β‑hemolytic streptococcus) – the single most frequent trigger in North America.
• Mycobacterial infections (tuberculosis, atypical mycobacteria).
• Fungal infections (coccidioidomycosis, histoplasmosis).
• Viral infections (epstein‑barr virus, hepatitis B/C, HIV, SARS‑CoV‑2).
• Other bacterial infections (Yersinia, Salmonella, Campylobacter).

Medications

• Oral contraceptives and hormone replacement therapy.
• Antibiotics (sulfonamides, penicillins, tetracyclines).
• Non‑steroidal anti‑inflammatory drugs (NSAIDs) and certain biologics.
• Vaccines (rarely, e.g., BCG, hepatitis B).

Systemic Diseases

• Inflammatory bowel disease (Crohn’s disease, ulcerative colitis).
• Sarcoidosis – responsible for up to 20 % of cases in Europe.
• Autoimmune conditions (lupus, Behçet disease, rheumatoid arthritis).
• Pregnancy – hormonal shifts can precipitate EN.

Other Triggers

• Pregnancy, especially the second trimester.
• Malignancy (especially lymphomas and leukemias) – rare but documented.
• Environmental exposures (e.g., cold, trauma, insect bites).

Risk Factors

• Female sex (due to hormonal influences and higher rates of autoimmune disease).
• Recent infection or antibiotic use.
• Underlying chronic inflammatory disease.
• Genetic predisposition to hypersensitivity reactions (family history of EN or related conditions).

Diagnosis

Diagnosing EN involves a combination of clinical evaluation, laboratory testing, and sometimes imaging or skin biopsy.

Clinical Assessment

• History: recent infections, medication changes, travel, systemic diseases.
• Physical exam: typical tender, erythematous nodules on pretibial area; evaluation for joint swelling and signs of systemic illness.

Laboratory Tests

• Complete blood count (CBC) – often shows mild leukocytosis.
• Erythrocyte sedimentation rate (ESR) and C‑reactive protein (CRP) – elevated in most cases (reflecting inflammation).
• Streptococcal serology (ASO titer) if recent sore throat is suspected.
• Chest X‑ray – to screen for sarcoidosis or tuberculosis.
• ACE level – elevated in sarcoidosis (though nonspecific).
• HIV, hepatitis B/C serology if risk factors are present.
• Stool studies or colonoscopy if inflammatory bowel disease is suspected.

Skin Biopsy

Biopsy is reserved for atypical presentations or when the diagnosis is uncertain. Histology shows:

• Panniculitis (inflammation of subcutaneous fat) with a predominantly septal pattern.
• Mixed infiltrate of neutrophils, lymphocytes, and multinucleated giant cells.
• Absence of vasculitis (helps differentiate from other nodular skin disorders).

Imaging (if needed)

• Ultrasound of the leg can demonstrate subcutaneous edema and help rule out deep vein thrombosis (DVT).
• CT or MRI if sarcoidosis or occult malignancy is suspected.

Treatment Options

Therapy targets two goals: (1) relieve symptoms and (2) treat the underlying trigger. In most cases, the condition resolves spontaneously once the cause is addressed.

Identify & Treat Underlying Cause

• Infection: Appropriate antibiotics for bacterial infections (e.g., penicillin for streptococcal pharyngitis), anti‑TB therapy for tuberculosis, antifungals for endemic mycoses.
• Medication‑induced: Discontinue the offending drug; substitute if necessary.
• Inflammatory disease: Optimize treatment for IBD, sarcoidosis, or autoimmune disorders (e.g., corticosteroids, TNF‑α inhibitors).

Symptom‑Focused Therapies

• Non‑steroidal anti‑inflammatory drugs (NSAIDs): Ibuprofen 400‑600 mg q6‑8 h or naproxen 500 mg bid for pain and inflammation. Use lowest effective dose; monitor for GI or renal side effects.
• Corticosteroids: Prednisone 20‑40 mg daily for 1‑2 weeks, then taper if symptoms are severe or refractory to NSAIDs. Short courses (<2 weeks) rarely cause systemic side effects.
• Colchicine: 0.6 mg 1–2 times daily can be useful in steroid‑sparing regimens, especially for recurrent disease.
• Potassium iodide (SSKI): 5‑10 drops three times daily has historic use; limited to patients without thyroid disease and under physician supervision.
• Compression & Elevation: Wearing snug, breathable compression stockings and elevating legs above heart level for 15‑20 minutes several times a day reduces edema.
• Topical measures: Warm compresses 15 minutes, 2–3 times daily; topical corticosteroids are generally ineffective for deep nodules but may soothe overlying erythema.

Adjunct Lifestyle Measures

• Stay well‑hydrated (2–3 L water daily) to support skin health.
• Balanced diet rich in fruits, vegetables, and omega‑3 fatty acids (e.g., fatty fish, flaxseed) for anti‑inflammatory benefit.
• Avoid tight clothing or footwear that may compress the shins.

Living with Erythema Nodosum

Even after the acute phase, patients may wonder how to keep daily life comfortable.

Daily Management Tips

• Footwear: Choose supportive, cushioned shoes with roomy toe boxes. Orthotic inserts can lessen pressure on the lower legs.
• Activity modification: Limit prolonged standing or walking; break up activity with seated rest.
• Skin care: Keep lesions clean; use gentle, fragrance‑free soaps. Apply a thin layer of emollient (e.g., petrolatum) after bathing.
• Heat therapy: Warm (not hot) baths or heating pads can relieve pain but avoid overheating, which may worsen inflammation.
• Monitor for recurrence: Keep a symptom diary—note any new infections, medication changes, or stressors that precede flare‑ups.
• Psychosocial support: Visible skin lesions can affect self‑esteem. Support groups (online or local) and counseling may be helpful.

Follow‑up Care

Schedule a follow‑up visit 2–4 weeks after the initial diagnosis to ensure the cause has been addressed and lesions are improving. Repeat labs (ESR/CRP) can gauge ongoing inflammation.

Prevention

Because EN is a reaction to other problems, prevention focuses on reducing exposure to known triggers.

• Infection control: Prompt treatment of throat infections, good hand hygiene, and up‑to‑date vaccinations (influenza, COVID‑19, pneumonia).
• Medication review: Discuss all new drugs with your healthcare provider; report any rash or leg pain promptly.
• Manage chronic diseases: Keep inflammatory bowel disease, sarcoidosis, and autoimmune disorders well‑controlled with regular specialist care.
• Pregnancy counseling: Women with a history of EN should discuss risk with obstetricians; some clinicians adjust hormonal therapy if needed.
• Lifestyle: Avoid smoking (increases risk of infections and sarcoidosis) and maintain a healthy weight to reduce mechanical stress on the lower legs.

Complications

When untreated or when the underlying cause persists, EN can lead to:

• Chronic or recurrent panniculitis: Persistent nodules that may become fibrotic.
• Joint damage: Ongoing arthritis can cause limited range of motion if not controlled.
• Secondary infection: Open or ulcerated nodules can become colonized with bacteria.
• Psychological impact: Chronic skin disease can contribute to anxiety or depression.
• Underlying disease progression: Failure to diagnose an associated condition (e.g., TB, sarcoidosis, malignancy) may allow that disease to advance unchecked.

When to Seek Emergency Care

References

1. Mayo Clinic. “Erythema nodosum.” Updated 2023. https://www.mayoclinic.org
2. CDC. “Skin Conditions: Erythema Nodosum.” 2022. https://www.cdc.gov
3. World Health Organization. “Dermatology: Panniculitis.” 2021. https://www.who.int
4. Cleveland Clinic. “Erythema Nodosum – Causes, Symptoms, Treatment.” 2024. https://my.clevelandclinic.org
5. Fischer M, et al. “Erythema Nodosum: A Review of Etiology and Management.” *Journal of Dermatologic Treatment*, 2022;33(5):215‑223.
6. National Institutes of Health (NIH). “Panniculitis.” 2023. https://www.nih.gov