Hello, thanks for the question.
To begin with, the underlying causes for vitiligo are poorly understood though there are several triggers which have been associated with development of the condition. These triggers can range from emotional stress/trauma, exposure to certain industrial chemicals or even physical trauma (e.g sunburn, or in your case, cuts or scratches).
This appearance of vitiligo along areas of trauma is something described as Koebner's phenomenon. Certain skin conditions (including vitiligo) have been found to form on skin along lines of irritation or trauma. Like the image below shows, sometimes "trauma" can be from everyday activities such as friction from clothing.
Based on what you have mentioned, your skin condition may be triggered by physical trauma and it is important to note that further scratching may aggravate it.
While vitiligo is not typically associated with itch, depending on which study you reference, as many as 20% of patients may complain of itching.
If you are concerned about the appearance of new areas of depigmentation, I would recommend seeking out a doctor you are comfortable with for a review and confirmation of your condition as well as for further advice. Hope this helped!
Best Regards
Dr Chris Lim
