Erythema Nodosum in Lupus: Clinical Description
Erythema nodosum (EN) in lupus presents as raised, tender, red or violet subcutaneous nodules measuring 1-5 cm in diameter, most commonly affecting the extensor surfaces of the extremities, particularly the anterior tibial areas. 1
Key Clinical Features
The lesions are characterized by:
- Appearance: Raised, tender subcutaneous nodules with red or violet coloration
- Size: 1-5 cm in diameter
- Location: Predominantly on extensor surfaces, especially the anterior shins, though can involve trunk or upper extremities 1
- Texture: Firm, palpable nodules beneath the skin surface
- Timing: Usually occurs during periods of active lupus disease activity 2
Associated Symptoms
EN in lupus often presents with systemic manifestations including:
- Arthralgia
- Fatigue
- Fever (when disease is active)
Diagnostic Approach
Clinical diagnosis is typically sufficient and biopsy is not usually necessary. 1 A firm clinical diagnosis can normally be made based on the characteristic appearance and distribution. If biopsy is performed in atypical cases, histology reveals non-specific focal panniculitis 2, 1.
Critical Differential Diagnosis
Metastatic Crohn's disease must be excluded, as it can appear as solitary or multiple nodules, plaques, ulcers, or violaceous perifollicular papules at any site, with non-caseating granulomas on histology 1. This distinction is crucial as the management differs significantly.
Important Clinical Pitfall
Do not confuse EN with lupus erythematosus tumidus (LET), which can clinically mimic EN but represents a different entity. Recent case reports 3, 4 document patients initially misdiagnosed with EN who actually had LET. LET requires histopathological confirmation and responds to hydroxychloroquine, whereas EN in lupus typically parallels underlying disease activity and may require systemic corticosteroids 1.
The prevalence of EN in inflammatory bowel disease-associated conditions ranges from 4.2-7.5%, and when it occurs in lupus, it is closely related to disease activity despite potential genetic links 2.