what's wrong with my cat?

About 3 days ago, after returning from a trip out of town, I noticed my beloved cat, Powder has these 2-3 inch areas around his limbs where his skin is showing through his fur. Powder is 3, he lives with 2 other cats (none of which go outside--ever.) In fact, he hasn't been outside except for going to and from the vets sice he was a kitten. He is slightly overweight @ ~16 lbs, but he is big-boned. He hasn't exhibited any symptoms of illness except for his ear mites in almost 2 years. the other 2 cats are also healthy. He seems fine, maybe a little less energetic, but mostly fine except for this strange condition. There are no fleas in the house either. Does anyone know what this might be? I am taking him to the vet tomorrow, but the worrying is driving me crazy.

My guess would be that you being gone stressed him out. Lots of cats when stressed will lick and pull thier furr out. Of course, just to be on the safe side, I would keep the appt for tomorrow.