Extracutaneous manifestations (due to sterile neutrophilic infiltrates):
Culture-negative pulmonary infiltrates most common
cardiovascular, CNS, GI, eyes, liver, spleen, bones, lymph nodes
Initial lesion: bite-like, small, red papule or pustule (many patients attribute spider bite)
Changes into larger, ulcerative lesion
Two primary variants:
Classic ulcerative form - usually on legs, deep ulceration, violaceous border along ulcer bed
Superficial, atypical form - hands/forearms/face, vesiculopustular
Less common variants: 1) Peristomal<unk> , 2) Genital<unk>  (must differentiate from STI), 3) Pyostomatitis vegetans (intraoral)
Culture-negative pulmonary infiltrates most common
cardiovascular, CNS, GI, eyes, liver, spleen, bones, lymph nodes
Classic ulcerative form - usually on legs, deep ulceration, violaceous border along ulcer bed
Superficial, atypical form - hands/forearms/face, vesiculopustular
Less common variants: 1) Peristomal<unk> , 2) Genital<unk>  (must differentiate from STI), 3) Pyostomatitis vegetans (intraoral)
Pyoderma gangrenosum
Systemic diseases
Erythema infectiosum
Neutrophilic dermatoses 
Cutaneous larva migrans
Calciphylaxis - very important to differentiate due to treatment
Purpura fulminans
Arterial/venous insufficiency