Which of the following statements are true regarding erythema nodosum?

E) A, B, and C are correct

Statements A, B, and C are all accurate regarding erythema nodosum, making option E the correct answer. 1, 2

Analysis of Each Statement

Statement A: Painful nodules on the lower limbs (hypodermitis) - TRUE

Erythema nodosum is definitively characterized by raised, tender, red or violet subcutaneous nodules of 1-5 cm in diameter that commonly affect the extensor surfaces of the extremities, particularly the anterior tibial areas 1, 2. The histology reveals a non-specific focal panniculitis (inflammation of subcutaneous fat) 2. The nodules are consistently described as painful and tender across all guideline evidence 1, 3, 4, 5.

Statement B: Unlike pyoderma gangrenosum, there is no ulceration - TRUE

This is a critical distinguishing feature. The guidelines explicitly state that erythema nodosum does not ulcerate and usually resolves without atrophy or scarring 1. In direct contrast, pyoderma gangrenosum involves necrosis of the dermis leading to deep excavating ulcerations containing purulent material 1, 2. This distinction is clinically important for differential diagnosis.

Statement C: Usually caused by streptococcal infection - PARTIALLY TRUE

While streptococcal pharyngitis is identified as the most common identifiable cause when a trigger can be found 3, 4, it's important to note that erythema nodosum is idiopathic in approximately 50% of cases 5. The pathogenesis involves a type IV hypersensitivity reaction, with triggers identified in only about 40% of patients 1. Other common causes include tuberculosis, sarcoidosis, inflammatory bowel disease, medications, and pregnancy 3, 4, 5.

Statement D: Paracetamol is the treatment of choice - FALSE

This statement is incorrect. The guidelines clearly indicate that:

• Treatment is based on the underlying disease (particularly IBD when present) 1, 2
• NSAIDs (not paracetamol) are first-line for pain management 3, 5, 6
• Systemic corticosteroids are required in severe cases 1, 2
• For resistant or recurrent cases, immunomodulators (azathioprine) or anti-TNF agents (infliximab, adalimumab) may be used 1, 2

Clinical Approach

Diagnostic criteria: Clinical diagnosis based on characteristic tender, erythematous nodules on lower extremities; biopsy only needed in atypical cases 1, 7

Initial workup should include:

• Complete blood count with differential
• ESR and/or CRP
• Throat culture or rapid streptococcal antigen test
• Anti-streptolysin O titers
• Chest radiograph (to evaluate for tuberculosis, sarcoidosis)
• Risk stratification for tuberculosis 3, 5

Treatment hierarchy:

1. Identify and treat underlying cause
2. Bed rest and leg elevation
3. NSAIDs for pain control (not paracetamol)
4. Systemic corticosteroids for severe cases
5. Immunomodulators or anti-TNF for refractory/recurrent disease 1, 2, 3, 5, 6

Common Pitfalls

• Don't assume it's always streptococcal - remember the 50% idiopathic rate and broad differential including sarcoidosis, IBD, tuberculosis, and medications
• Don't confuse with pyoderma gangrenosum - the absence of ulceration is key
• Don't use paracetamol as first-line - NSAIDs are the appropriate analgesic choice
• Don't biopsy routinely - clinical diagnosis is usually sufficient unless presentation is atypical 1, 7