Diagnosis

Erythema nodosum

Etiology

Cause [sc3][qfm]

1. Idiopathic (55%)

2. Infection (28-48%): 

   • Bacterial: Streptococcal pharyngitis, Yersinia spp., mycoplasma pneumonia, chlamydia, histoplasmosis, coccidioidomycosis, mycobacteria, Tuberculosis, Leprosy, Tularemia, Cat scratch disease (Bartonella species), Leptospirosis, Brucellosis, Psittacosis, Chlamydia trachomatous, Lymphogranuloma venereum, Campylobacter spp., rickettsiae, Salmonella spp., psittacosis, syphilis

   • Virus: herpes simplex virus, Epstein-Barr Virus (mononucleosis), hepatitis B/C, human immunodeficiency virus, Para vaccinia

   • Fungal: Coccidioidomycosis, Histoplasmosis, Blastomycosis

   • Parasitic: amoebiasis, giardiasis

3. Systemic disease: Sarcoidosis (11-25%), Ulcerative colitis, Crohns disease, Behcets disease, Sjogren disease, Celiac disease, Autoimmune hepatitis, Spondiloarthropathy, Kawasaki, Takayasu, Blau Syndrome, CAPS, HIDS, Sweet syndrome, Carcinoid, Sarcoma, Whipple disease

4. Drugs (3-10%): Sulphonamides, amoxicillin, Macrolides, Cephalosporin, PPI, Everolimus, Aspirin, Contraceptives, Azathioprine, Phenitoin, Valproate, bromides, iodides, TNF-alpha inhibitor

5. Pregnancy (2-5%)

6. Malignancy: Leukemia, Lymphoma, Occult malignancies

7. Vaccination: BCG, DTaP, HPV, SARS-CoV-2

Pathophysiology [sc3][qfm]

1. A cutaneous type IV delayed hypersensitivity reaction to various antigens

2. Deposition of immune complexes in the venules of subcutaneous fat

3. Oxygen free radicals + TNF-alpha --> granuloma formation

Epidemiology

Incidence per 100.000 [ben][ozw]

Approach

• Blood test: CRP, ESR [qfm]

• Chest x-ray

• Throat culture: streptococci, antigen test, antistreptolysin O titer, PCR

• Mantoux test

• Stool culture: parasites

• Cutaneous biopsy

Treatment

Painful but self-limited disease lasting 3–6 weeks. Supportive therapy, including bed rest and avoidance of contact irritation of affected areas [sc3]

1. Treatment of the underlying disorder

2. Pain --> NSAIDs

3. Systemic steroids (1 mg/kg) may be used until resolution if underlying infection and malignancy have been excluded

4. Colchicine if coexistent Behçet's syndrome

5. Other agents: [yft]

   • Intra-lesional corticosteroid

   • Dapsone

   • Hydroxychloroquine

   • Anti-TNF monoclonal antibodies

   • Thalidomide

   • Methotrexate

Differential diagnoses

Alpha1-antitrypsin deficiency, Behcet's disease, Cellulitis, Crohn disease, Erysipelas, Erythema induratum, Familial mediterranean fever, Fat necrosis, Fracture, Insect Bite, Leukemia, Lymphoma, Phlebitis, Sarcoidosis, Scleroderma, Systemic lupus erythematosus, Thrombophlebitis, Ulcerative colitis, Urticaria