I have an 11 year old collie husky mix who has the following symptoms:
1. his hair has stopped growing. We get him shaved down and his hair no longer grows back.
2. he has lost a lot of weight in the past couple of years. Something like 15 pounds -- about 25% of his total weight. He is fed a cup of dry food with about 6 ounces of canned food with each meal and he eats approximately half to three quarters of that.
3. he occasionally has diarrhea. This might be associated with periods where he ate more than normal or there were small changes in his diet. For instance, around thanksgiving he was given a small amount of turkey in his meals for about a week, at the end of which he had a diarrhea episode.

Is there anything specific that could cause all of this? We are taking him to the vet, but am looking up potential causes on my own as well.

The list of potential causes is long.

The vet will have some good ideas.

There is a rather long list of possible causes of digestive problems, which includes intestinal parasites, fungal infections, food intolerances, pancreatitis, loss of pancreatic function, malabsorption of food, bacterial growth in the intestines, colitis, polyps, cancer, thryoid dysfunction, among others. Some of these are related to each other.

When you take him to the vet, be sure to take in a stool sample so they can screen for parasites, and ask for a complete blood workup. It will cost a bit, but may save you some time and grief down the road.