History:

Patient of Dr 

44 yr old diabetic patient whom I have been seeing for management of fairly deep diabetic foot ulcer over the1st metatarsal head. Has been doing well and suddenly decompensated over the weekend with swelling, redness, large bulla that ruptured and then developing of gangrenous skin.

I am wondering if this could be Ecthyma Gangrenosum vs necrotizing cellulitis?

Due to diabetic neuropathy he does not have a lot of pain - does the lack of pain in a diabetic patient r/o necrotizing fasciitis? 

No The centre of an area of necrotising fasciitis is painless anyway.  Necrotizing cellulitis is probably the underlying problem together with the diabetes and poor circulation. Lack of much pain shouldn't fool you.
He might end up w amputation and I would admit him immediately for iv antibiotics and imaging and hyperbaric oxygen maybe.