Summary

Erythema nodosum (EN) is the most common form of panniculitis (inflammation of subcutaneous fat). It presents as tender, red-to-violet nodules typically on the anterior shins (tibial surface). EN is a reactive condition — a hypersensitivity response to various triggers including infections (especially streptococcal), drugs (sulfonamides, OCP), sarcoidosis, inflammatory bowel disease (IBD), and TB. Approximately 50% of cases are idiopathic. The nodules never ulcerate and heal like bruises, leaving temporary pigmentation without scarring. Diagnosis is clinical; investigations focus on identifying the underlying cause. Treatment is supportive: NSAIDs, rest, compression, and treating the precipitating condition.

Key Facts

• Definition: Septal panniculitis; Inflammation of subcutaneous fat
• Appearance: Tender, red/violaceous nodules on shins; Never ulcerate
• Healing: Like bruises — red → purple → yellow → brown
• Peak incidence: Young adults (20-40 years); Female > Male (3:1)
• Idiopathic: ~50% of cases
• Causes (NO DOSUM): No cause, Drugs, Oral contraceptive, Sarcoidosis, UC/Crohn's, Microbiology

Clinical Pearls

"SHINS That Never Ulcerate": Erythema nodosum classically affects the anterior tibial surface. Unlike other panniculitides, EN NEVER ulcerates and heals without scarring.

"Löfgren's Syndrome = EN + Sarcoidosis": Löfgren's syndrome is the triad of erythema nodosum, bilateral hilar lymphadenopathy, and often polyarthritis. Get a chest X-ray in all EN cases.

"Think Strep": Streptococcal pharyngitis is the commonest infectious cause of EN. Check ASOT titre in unexplained cases.

"NO DOSUM Mnemonic": No cause (idiopathic); Drugs (sulfonamides, penicillin, OCP); Oral contraceptive; Sarcoidosis; UC/Crohn's; Microbiology (Strep, TB, Yersinia).

Why This Matters Clinically

EN is often the first sign of an underlying systemic condition — particularly sarcoidosis, TB, or IBD. Identifying and treating the cause is more important than treating the skin lesions themselves.[1,2]

Skin Examination

Joint Examination

• Ankle/knee tenderness (arthralgia)
• May have effusion (arthritis)

Key References

What is erythema nodosum?

Erythema nodosum is a skin condition that causes painful, red lumps under the skin, usually on the shins. It's caused by inflammation in the fatty layer beneath the skin.

What causes it?

It can be triggered by:

• Infections (like a sore throat)
• Certain medicines (the pill, antibiotics)
• Underlying conditions (sarcoidosis, bowel disease)
• Often no cause is found

What are the symptoms?

• Painful, tender lumps on the shins
• Feeling unwell, tired, feverish
• Aching joints

How is it treated?

• Rest and elevate your legs
• Anti-inflammatory painkillers (like ibuprofen)
• Treating the underlying cause
• The lumps usually go away on their own in a few weeks

Is it serious?

The skin condition itself is not serious and heals without scarring. However, it can be a sign of an underlying condition that needs treatment.

High-Yield Exam Topics

Sample Viva Question

Q: A 25-year-old woman presents with painful nodules on her shins. What is your differential and approach?

Model Answer: The most likely diagnosis is erythema nodosum — tender red nodules on the shins that never ulcerate. Differential includes other panniculitides (less common). I would take a history for precipitants: recent sore throat (streptococcal), drugs (OCP, sulfonamides), GI symptoms (IBD), cough (sarcoidosis, TB). Investigations: CXR (hilar lymphadenopathy suggests sarcoidosis), ASOT (streptococcal), ESR/CRP. If sarcoidosis suspected, check ACE level. Treatment: identify and treat underlying cause; NSAIDs for pain; rest and elevation. EN is self-limiting but recurs if the cause persists.

Last Reviewed: 2025-12-24 | MedVellum Editorial Team