Erythema Nodosum Differential Diagnosis

The differential diagnosis for erythema nodosum, a condition characterized by the sudden onset of tender, erythematous nodules or plaques most commonly found on the lower extremities, can be broad and includes various infectious, inflammatory, and neoplastic conditions. Here's a categorized approach to the differential diagnosis:

• Single Most Likely Diagnosis

  • Sarcoidosis: This is often considered a leading cause of erythema nodosum, particularly when it presents as Lofgren's syndrome, which includes bilateral hilar lymphadenopathy, joint symptoms, and erythema nodosum. The justification for this being the single most likely diagnosis lies in its relatively high prevalence among causes of erythema nodosum and the classic presentation of Lofgren's syndrome.

• Other Likely Diagnoses

  • Infections (Streptococcal, Tuberculosis, Fungal): Various infections can trigger erythema nodosum, with streptococcal infections being a common cause, especially in children. Tuberculosis and fungal infections are also known triggers.
  • Inflammatory Bowel Disease (IBD): Both Crohn's disease and ulcerative colitis can be associated with erythema nodosum, reflecting the systemic nature of these diseases.
  • Pregnancy: Erythema nodosum can occur during pregnancy, often in the second or third trimester, though the exact mechanism is not well understood.
  • Medications (e.g., Sulfonamides, Penicillin): Certain medications can induce erythema nodosum as an idiosyncratic reaction.

• Do Not Miss Diagnoses

  • Lymphoma: Though rare, lymphoma can present with erythema nodosum, and missing this diagnosis could have significant implications for patient outcomes.
  • Infectious Endocarditis: This condition, though uncommon as a cause of erythema nodosum, is critical to identify due to its high morbidity and mortality if left untreated.
  • Deep Vein Thrombosis (DVT): While not a direct cause, the pain and swelling from DVT can sometimes be confused with erythema nodosum, making it essential to differentiate the two.

• Rare Diagnoses

  • Beheet's Disease: A form of vasculitis that can present with a wide range of symptoms, including erythema nodosum-like lesions.
  • Sweet Syndrome: Also known as acute febrile neutrophilic dermatosis, it can present with skin lesions that might be confused with erythema nodosum.
  • Erythema Induratum: A condition characterized by recurring nodules on the calves, often associated with tuberculosis.

Each of these conditions has a unique set of characteristics and associated findings that can help guide the diagnosis. A thorough history, physical examination, and appropriate laboratory tests are essential for accurately diagnosing the underlying cause of erythema nodosum.