It sort of looks as if there is a narrow section of the casque that has been damaged (possibly an old burn?) and may be lifting away from the rest. If the tissue in that narrow strip is dead it will eventually dry out and slough off. The separation of the dead area and the live area may be what you are seeing.
I will say I just ran into this situation with my veiled. Part of his casque started to peel away, I assume from a burn or his casque never shed properly and the left over skin cut the circulation off. The part peel away. Be careful and keep an eye on it. When my veiled's peeled away the top part left a small open sore. I kept it clean and applied polysporin on it. Just a head up.
Thanks to both of you for the input. I am thinking that it is a burn even though I had thought that I avoided the threat of thermal burns. I had lifted the lights off his cage and checked the temperature with my "Zilla" thermometer/humidity and it was in the 90s. The mistake that I think I made is: I had a branch high up in the cage and my Cham would sit on that with his casque touching the top of the cage directly under the light. I also caught him scrapping his casque along the surface of the screen. So I have lowered that branch. I tried to put bacitracin (single antibiotic ointment) on the affected area but he would not have it. I will try again after the piece has sloughed off. csmolins89: How did your Cham heal?
I have the Zilla Digital Hygrometer and Thermometer and its reviews for temperature readings have been good. It appears to me that when my Cham had his head pressed up against the top of the cage is when the burn occurred.
I would advise others to keep their chams from being able to do this.