Vizsla with dandruff and low weight

Question
I have an unneutered 2yr old male Vizsla that has always been on the thin side no matter what he is eating.  He has a great appetite and is normally very active. I (reluctantly) just took him off of puppy food and switched to the same brand for active large breeds.  His weight has always worried me, though.  He weighs 48lbs.  Recently I have noticed a few changes though that have me concerned that it could be a thyroid issue:
*Excessive dandruff
*Tires out after 10-15 mins of normal play activity
*Odd and excessive chewing and licking on his paws and nails (which are groomed reg)
*No additional weight gain

My vet is tends to charge about twice as much as other vets for everything, so an idea of what he should be looking and testing for before I go would be great!!  Thanks!!  

Answer
It is very uncommon for dogs to get hyper-thyroid. They usually tend to get hypo-thyroid, which is low thyroid. With that you have weight gain, bad coats and lethargy.

His problem could be in the diet he eats (you didn't say what brand it is) and the fact that his kidneys are frying through way too much protein for an adult dog. Him being intact is also an issue with his weight. Too much testosterone could case the imbalance you are seeing. Since he isn't breeding stock you really need to have him neutered, which could solve half or more of his problems.

Active Breed foods have more fat in them- fat is twice as efficient than protein at creating energy. So active breed foods have more fat for energy but a normal amount of protein. Puppy food does not, however. It is made for growth, not weight gain. So your dog hasn't been getting a proper amount of nutrition for over a year.

That could also be part of the problem. I think some blood work is certainly in order here but if it is all negative then you need to concentrate on neutering and diet. A good diet (such as Science Diet) has all the nutrients he will need for his coat (dandruff) and his weight and energy needs.

When a dog eats and eats and doesn't gain weight or eats so much that he is obese- both of these are forms of malnutrition.
In the case of the obese dog these are dogs that eat and eat but never get any nutrition from their food to meet their energy needs. This is what I call trying to get an pound of protein from a box of crackers. It just isn't going to happen. So the dog keeps eating and getting treats but is malnourished the whole time.

Same for the underweight dog. It is usually the intact ones that have the same food issues but their hormones are out of whack too so they don't gain.
Now there are some diseases that can cause the weight loss also, but from what you are saying he has always been skinny. You didn't mention his stool either but how it looks has a lot to do with his ability to absorb his food also.

Dogs can get many mal-absorption disorders that will cause weight loss or failure to thrive.

So get him in for a blood panel then get him neutered and onto some good food. You should see a difference in a month-barring any other medical issues.
Let me know how he does and what his results are.