Erythema Nodosum

Erythema nodosum is a form of panniculitis (inflammation of the subcutaneous fat layer) characterized by tender; red nodules typically located on the shins.

Aetiology

The disease originates from a hypersensitivity reaction triggered by various underlying conditions. The causes can be categorized as infectious, inflammatory disorders, medications, and other triggers.

Infections:

  • Streptococcus pyogenes (most common in children and young adults)

  • Mycobacterium tuberculosis

  • Viral infections (e.g., Epstein-Barr virus, hepatitis B and C)

  • Fungal infections (e.g., coccidioidomycosis)

Inflammatory disorders:

  • Sarcoidosis (a major cause in adults)

  • Inflammatory bowel disease (Crohn’s disease and ulcerative colitis)

  • Behçet’s disease

Medications:

  • Oral contraceptives

  • Sulfonamides and penicillins

Other triggers:

  • Pregnancy: Hormonal changes during pregnancy can act as a trigger

  • Malignancies e.g. (Leukaemia or Lymphoma)

  • Idiopathic Cases: Up to 55% of cases have no identifiable cause

Pathophysiology

The exact mechanism of erythema nodosum is not fully understood but involves a type IV delayed hypersensitivity reaction. In response to antigens from infections, systemic diseases, or drugs, immune complexes deposit in the subcutaneous fat and venules, leading to septal panniculitis without vasculitis. This immune-mediated inflammation results in the characteristic nodules seen on the surface.

Clinical Presentation

Erythema nodosum typically presents with tender, erythematous, raised nodules ranging from 1 to 5 cm in diameter, most commonly found on the anterior tibial surfaces of both shins. Over time, the nodules change color, evolving from bright red to bluish-purple and yellow-green, resembling the stages of a bruise.

Systemic symptoms like fever, malaise, and joint pain may accompany the nodules, particularly in cases linked to infections.

Diagnosis

The diagnosis of EN is primarily clinical, supported by a detailed patient history and physical examination. Additional investigations to identify the underlying cause include:

Laboratory Tests:

  •  Complete blood count (CBC): May show leukocytosis.

  •  Elevated inflammation markers like Erythrocyte sedimentation rate and CRP

  •  Antistreptolysin O (ASO) titers: Elevated in streptococcal infections.

  •  Faecal calprotectin to exclude inflammatory bowel disease

Imaging Studies:

  • Chest X-ray: Essential in evaluating sarcoidosis or tuberculosis.

Skin Biopsy can confirm septal panniculitis without vasculitis but are rarely required.

Therapy

The treatment of erythema nodosum focuses on addressing the underlying cause and alleviating symptoms. Usually cooling and resting are sufficient to alleviate symptoms, but in more severe cases, NSAIDS or systemic corticosteroids can be necessary in order to tackle the ongoing inflammation and the pain.

Lesions typically resolve spontaneously within 3 to 6 weeks without scarring. However, recurrence can occur if the underlying cause persists.

References

  1. Jorizzo JL, Daniels SE, Schlesinger TE. "Dermatologic Signs of Systemic Disease." New England Journal of Medicine. 2020;382:167-179.

  2. Mert A, Ozaras R, Tabak F, et al. "Erythema Nodosum: Causes and Management." Clinical Dermatology. 2018;36(3):281-289.

  3. Blauvelt A, Cohen DE. "Hypersensitivity Reactions in Dermatology." Journal of the American Academy of Dermatology. 2019;81(5):1218-1227.

  4. European Dermatology Forum. "Guidelines for the Diagnosis and Management of Erythema Nodosum." 2021. Available at: [www.edf.org/guidelines](http://www.edf.org/guidelines).