Diagnosis
Diagnosis is clinical. A deep punch biopsy or an incisional biopsy may be performed in cases where the diagnosis is unclear. Microscopic examination will reveal a septal panniculitis with acute and chronic inflammation in the fat and around blood vessels.
Once EN is diagnosed, additional evaluation needs to be performed to determine the underlying cause. A complete blood count, erythrocyte sedimentation rate (ESR), antistreptolysin-O (ASO) titer, urinalysis, throat culture, intradermal tuberculin test, and chest x-ray are part of the initial examination.
The ESR is initially very high, and falls as the nodules fade. The ASO titer is high in cases associated with a streptococcal throat infection. A chest X-ray should be performed to rule out pulmonary diseases. Hilar lymphadenopathy may be due to tuberculosis, sarcoidosis, or Löfgren syndrome (a form of acute sarcoidosis with erythema nodosum, bilateral hilar adenopathy, fever, and often accompanied by joint symptoms).
Read more about this topic: Erythema Nodosum