Systemic diseases
Neutrophilic dermatoses (Sweet, Behcet's disease, etc.)
Calciphylaxis - very important to differentiate due to treatment
Arterial/venous insufficiency
Blastomycosis
Hidradenitis suppurative
TB gumma, mycobacterial infections
Malignancy (squamous cell)
Vasculitis
Ecthyma<unk>  (pseudomonas)
Neutrophilic dermatoses (Sweet, Behcet's disease, etc.)
Calciphylaxis - very important to differentiate due to treatment
Arterial/venous insufficiency
Blastomycosis
Hidradenitis suppurative
TB gumma, mycobacterial infections
Malignancy (squamous cell)
Vasculitis
Ecthyma<unk>  (pseudomonas)
Pyoderma gangrenosum
Systemic diseases
Erythema infectiosum
Neutrophilic dermatoses 
Cutaneous larva migrans
Calciphylaxis - very important to differentiate due to treatment
Purpura fulminans
Arterial/venous insufficiency