Erythema Nodosum

Related Subjects: | Nikolsky's sign | Koebner phenomenon | Erythema Multiforme | Pyoderma gangrenosum | Erythema Nodosum | Dermatitis Herpetiformis | Lichen Planus | Acanthosis Nigricans | Acne Rosacea | Acne Vulgaris | Alopecia | Vitiligo | Urticaria | Basal Cell Carcinoma | Malignant Melanoma | Squamous Cell Carcinoma | Mycosis Fungoides (Sezary Syndrome) | Xeroderma pigmentosum | Bullous Pemphigoid | Pemphigus Vulgaris | Seborrheic Dermatitis | Pityriasis/Tinea versicolor infections | Pityriasis rosea | Scabies | Dermatomyositis | Toxic Epidermal Necrolysis | Stevens-Johnson Syndrome | Atopic Eczema/Atopic Dermatitis | Psoriasis

🌸 Erythema Nodosum (EN) is a hypersensitivity reaction presenting with painful, indurated, shiny, red-hot nodules (1–3 cm) — classically on the shins. Included as seen with Sarcoidosis which is on the MLA🦵

ℹ️ About

• Represents an immune-mediated panniculitis (inflammation of subcutaneous fat).
• Often associated with systemic disease or infections.
• Self-limiting but may recur.

🔬 Pathology

• Type IV hypersensitivity → immune response to foreign antigens.
• Causes septal panniculitis without vasculitis (key histological point).
• Legs affected due to poor lymphatic drainage and hydrostatic pressure.

🦠 Causes

• 📌 Bacterial: Streptococcus (most common), Tuberculosis, Leprosy, Yersinia.
• 🦠 Viral/Other infections: EBV, Chlamydia, Histoplasmosis, Toxoplasmosis, Salmonella, Campylobacter, Rickettsia.
• 💊 Drugs: Sulphonamides, OCP, Penicillin, Tetracyclines, Sulphonylureas.
• 🧬 Systemic conditions: Sarcoidosis, Behçet’s, IBD (Crohn’s/UC), Haematological malignancy, Pregnancy.
• ❓ Idiopathic in many cases.

🩺 Clinical Features

• Painful, red, hot nodules (1–3 cm) → typically on the shins.
• Lesions evolve: red → violaceous → bruise-like fade; no ulceration/scarring.
• Crops last 3–6 weeks, with new lesions appearing.
• Associated systemic features: fever, malaise, arthralgia.
• ♀️ More common in females (young adults).

🧾 Investigations

• Bloods: FBC, CRP/ESR, ASO titre, Serum ACE (for sarcoid).
• Microbiology: Throat swab (strep screen).
• Imaging: CXR for bihilar lymphadenopathy (sarcoid, TB).
• Tuberculosis screen (Heaf or Mantoux).

💊 Management

• Identify and treat underlying cause (e.g., strep, TB, IBD).
• Supportive: rest, leg elevation, compression stockings.
• Symptomatic: NSAIDs or potassium iodide.
• Severe/refractory: Colchicine, Dapsone, Corticosteroids (caution: exclude infection first!).
• Spontaneous resolution usually in 3–6 weeks, but full resolution may take up to 3–6 months.

🩺 Case 1 : Post-Streptococcal Infection

A 22-year-old woman presents with painful red nodules over both shins, fever, and sore throat 2 weeks ago. Throat swab grew group A streptococcus. Exam shows tender, raised, erythematous lesions on the anterior tibiae. Management: 💊 Treat underlying streptococcal infection (penicillin), NSAIDs for pain, bed rest, supportive care. Avoid: ❌ Ignoring possible underlying infection; avoid corticosteroids unless infection excluded.

🩺 Case 2 : Sarcoidosis

A 35-year-old woman presents with painful shin nodules, dry cough, and fatigue. CXR shows bilateral hilar lymphadenopathy. Diagnosis: sarcoidosis presenting with erythema nodosum and pulmonary involvement. Management: 🩺 NSAIDs for pain; systemic corticosteroids if significant pulmonary disease. Monitor with respiratory team. Avoid: ❌ Relying on NSAIDs alone if there is progressive sarcoidosis; avoid long-term steroids without specialist supervision.

🩺 Case 3 : Drug-Induced

A 40-year-old man develops painful nodules on his legs 3 weeks after starting sulfonamide antibiotics for a urinary tract infection. He is otherwise well with no systemic features. Management: 💊 Discontinue offending drug, symptomatic relief with NSAIDs, compression stockings if needed. Avoid: ❌ Re-challenging with the culprit drug; avoid unnecessary antibiotics in the future.