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 aka Erythema Contusiformis (a very appropriate descriptive name because the lesions often take on the look of a deep bruise) 
  
| • | mnemonic: e. nodosum is almost the “opposite” of nodular vasculitis (septal without vasculitis without ulceration vs. lobular with vasculitis with ulceration) |  
   
Etiology: (think of two in each category) 
| • | Infection:  beta-hemolytic strep pharyngitis (usually within 3 weeks of infection; increased ASO);   TB (associated with primary infection)     |  
 | • | Drugs: sulfonamides;      oral contraceptives (pregnancy also)     |  
 | • | Inflammatory: Sarcoidosis: (Löfgrens syndrome);     Inflammatory Bowel Disease: ulcerative colitis especially (often correlates with disease activity)        |  
   
clinical: 
| • | new lesions often accompanied by fever, chills, malaise and leukocytosis |  
 | • | never ulcerate (vs. nodular vasculitis) |  
 | • | resolve spontaneously within 3-6 weeks |  
   
Erythema Nodosum Migrans: 
| • | clinical variant (AKA Vilanova variant) |  
 | • | as lesion progresses, may assume arciform pattern with brightly erythematous edge |  
   
Treatment: 
| • | NSAIDS,  SSKI,  ILK,  PO steroids |  
 | • | SSKI - second line for me:  hard to find in the pharmacy (usually needs to be ordered);  patients don't like taking it (taste, frequency etc...) and I have not found it to be particularly effective |  
 | • | I usually start with Naproxen 250mg PO BID |  
   
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