Dermal Necrosis After Sclerotherapy?

I would highly recommend that you see a board certified dermatologist specializing in treating wounds.  

Post sclerotherapy ulcerations fortunately are uncommon but when they do occur they are usually difficult to heal.  Certainly vein specialists have expertise in this area and this is who I would recommend seeing.  Dermatologists and plastic surgeons trained in wound care may also be able to treat this.

Vein specialists know more about venous wounds than dermatologists (true and hard to believe). Cosmetic dermatologists are good when you need a peel or if you need facial fillers and Botox.

Of course, there are dermatologists that have expertise in venous disease and recognize how to treat this problem.

If the ulcer is without evidence of infection, electical stimulation therapy will help heal it. If it is active and has a lot of drainage, it can be treated with unna boot compression and antibiotics. If it is a healed ulcer with a resultant scar, it can be revised by a Board Certified Plastic Surgeon. Mobilization of tissue in the face of scarring in an individual who has a healed ulcer is prone to tissue necrosis and left best to plastic surgeons who are experts in this area - their expertise in microcirculation, raising tissue flaps, mobilizing tissue is unparalleled among other surgical specialists or dermatologists - that is what they are trained to do ...

I actually suggest you see a board-certified dermatologist experienced in treating wounds and in sclerotherapy (therefore familiar with its side effects). Dermatologists are the skin experts and the most adept with how to treat ulcerations in the skin. 

See a Board Certified Plastic Surgeon (American Board of Plastic Surgery). You may need a scar revision