Erythema Nodosum
A skin condition causing tender, red bumps under the skin, usually on the shins, representing an allergic reaction to infections, medications, or other diseases.
Emergency Management: None directly related to the rash itself, but underlying causes (like acute severe inflammatory bowel disease or systemic infections) may require urgent intervention.
Erythema nodosum (EN) is the most common form of panniculitis, presenting as an acute, self-limiting nodular eruption characterized by tender, erythematous, inflammatory nodules. The lesions are typically distributed symmetrically on the extensor surfaces of the lower extremities (pretibial areas).
Detailed Overview
EN is not a primary disease but a delayed-type hypersensitivity reaction (Type IV) to various antigenic stimuli. The sudden appearance of these painful nodules is often accompanied by systemic symptoms such as fever, malaise, and arthralgia. Identifying the underlying trigger is the most critical aspect of managing the patient, as EN can be the first manifestation of serious systemic diseases like sarcoidosis, tuberculosis, or inflammatory bowel disease.
Epidemiology & Demographics
Peak incidence is between 20 and 30 years of age. It is 3 to 6 times more common in women than in men.
Etiological Mechanism
Idiopathic in up to 50% of cases. The most common identifiable causes include Streptococcal pharyngitis (especially in children), oral contraceptives, sarcoidosis (Löfgren syndrome), and inflammatory bowel disease.
Primary Causes
Streptococcal Infections (Group A beta-hemolytic strep)
Sarcoidosis
Inflammatory Bowel Disease (Crohn's, Ulcerative Colitis)
Medications (Oral Contraceptives, Sulfonamides, Penicillins)
Tuberculosis and Endemic Fungi (Coccidioidomycosis)
EN is an immunologic response characterized by immune complex deposition and neutrophil infiltration in the septa of the subcutaneous fat. This delayed hypersensitivity reaction leads to septal panniculitis. Initially, the septa are widened by edema and a neutrophilic infiltrate. Over time, the infiltrate becomes predominantly mononuclear, with histiocytes and multinucleated giant cells forming Miescher radial granulomas (the histopathologic hallmark). There is no primary vasculitis.
Diagnostic Criteria & Guidelines
Diagnosis is mostly clinical based on the characteristic appearance and location of the nodules. A deep incisional biopsy (reaching the subcutaneous fat) is definitive, showing septal panniculitis with Miescher radial granulomas, but is rarely needed unless presentation is atypical. Extensive workup is required to find the underlying cause.
Management is primarily symptomatic as the condition is self-limiting (resolves in 3-6 weeks). Bed rest and leg elevation are crucial. NSAIDs: Indomethacin 25-50 mg TID or Naproxen 500 mg BID for analgesia and anti-inflammatory effect. Treat the underlying cause (e.g., Penicillin V 500 mg BID for 10 days for Strep pharyngitis).
Second-Line & Adjunctive Therapy
Potassium Iodide (SSKI) 300-900 mg daily in divided doses (causes rapid resolution but mechanism is unclear). Systemic corticosteroids (e.g., Prednisone 40 mg daily tapering over 2 weeks) can be used for severe, refractory cases ONLY AFTER infectious causes (TB, deep fungi) have been definitively ruled out.
Surgical & Procedural Management
None indicated, other than deep incisional skin biopsy for diagnosis in atypical or refractory cases.
Patient Counseling & Advice
Reassure the patient that while the nodules are extremely painful, they will not scar or ulcerate, and typically resolve completely within 4 to 6 weeks. Emphasize that the bruise-like color change is a normal part of the healing process.
Follow-Up & Monitoring Schedule
Follow up in 2-4 weeks to ensure resolution and to review the results of the diagnostic workup (chest x-ray, ASO titers) to rule out serious systemic diseases.
Preventive Strategies
Prompt treatment of streptococcal pharyngitis. Avoidance of known trigger medications if a prior episode was drug-induced.
Excellent. The nodules invariably resolve without atrophy or scarring within 3 to 6 weeks. Prognosis depends entirely on the underlying associated condition.