Muscular Atrophy in 2yr old dog

Hello, my dog has been diagnosed with muscular atrophy. His head began to dip on one side at the beginning of September 2024, I immediately took him to the vet (charity funded vet) who prescribed him prednisone which he has been on since. Over the past two months, further muscle has decreased in his body and the other side of his head has now dipped. I have increased his diet as he lost around 5kg since going on the steroids. His mobility has slowly began to decreased too. Although he can move his jaw well and can still walk, just unable to jump. He appears to be depressed (granted) but still has an amazing appetite. We feed him home cooked meals, which is usually beef or fish with either carrots, sweet potato or pumpkin and a small cup of grain, usually rice with a cup of kibble. I want to know if there is anything I can do differently or introduce to help my dogs quality of life. He is a 2 year old American Bully, I really want him around for aslong as possible. Any help is appreciated. Please see a before and after picture attached (August 2024 - now)

Hello and thank you for the pictures; he is still a very handsome boy and an interesting case.  I'm going to start with an annoyingly pernickety point, the sort that is important to vets but not necessarily to clients, so please bear with me.  Muscular atrophy is not a diagnosis; rather, it is a symptom; the symptom of muscle breaking down / losing bulk because it is not being used / contracting.  Other examples of symptoms (generally, not in connection with this case) might include head-aches, raspy breathing, fever, a smell of acetone on the breath or vomiting.  Like all the others, atrophy of muscles can be caused by different possibilities, so it is your vets' job to decide which one.  My list includes damage to the nerve supplying the muscle and once your vet has done a neurological (cranial nerve) examination, they might consider things like lumps and bumps, impinging on (possibly, the trigeminal nerve) and affecting its function.  Your mind might jump straight to cancer here, growing next to the nerve, but inflammatory processes can affect them too.  The same is true inside the head; changes of pressure or growths within the brain might put pressure on different nerves.  As well as this, there is a disease called temporal myositis, which is where the immune system attacks certain muscles in a dogs' face. The cases I have seen of this have all been bilateral i.e. occurring on both sides at once, but your vet could seek the opinion of a pathologist (if they don't know already) as to whether this can occur unilaterally (on one side).  In conclusion then, I have no firm answer yet but your vet could do tests in order to get to the bottom of this mystery.  

Wishing you both all the best of luck; please will you let us know what you've found out?