I have skin discoloration that is very progressive. i saw a dermatologist who said it is vitiligo. i also saw an md who doesn't think it's vitiligo. what should i do?

Vitiligo: Vitiligo is somewhat common. You may require long term follow up and your dermatologist will follow with you. Over time you will be able to determine it. Skin biopsy may be required if the skin discoloration worsens. You note it is progressive so that would go against vitiligo. Take a picture and repeat that next week to see how progressive. Same angle. Same view.

Was biopsy done?: If unsure if really vitiligo, talk to you dermatologist about doing skin biopsy to find out for sure what is going on.

Ask for a biopsy.: Sometimes it is difficult to determine whether vitiligo, depending on the background normal skin color. I never find fault with performing a simply biopsy. It is a fairly straight forward diagnosis with biopsy, especially if the pathologist performs a special stain on it. If vitiligo, there are various treatments available.

A 3rd opinion?: If the loss in pigmentation (not just discoloration) is progressive, you may have an autoimmune disorder. Discoloration is an entirely different subject. Perhaps you need to go to another dermatologist or an university center to pin down the diagnosis.