The skin and muscle wasting condition known as dermatomyositis is most common in the collie and shepherd breeds including the Shetland Sheepdog, Smooth and Rough Collies, German Shepherds, Australian Cattle Dog, Chow Chows and the Pembroke Welsh Corgi. The exact mode of inheritance of the condition is not completely understood but it is believed to be a dominant variable condition which means that as long as one of the parents has the disorder the puppies may show the condition. Each puppy in the litter may have the condition in various degrees from serious hair loss and muscle weakness to no obvious signs of the condition. Since there is this variation between the expression of the condition within a litter there may be other factors such as the overall health of the puppy as well as the development of the immune system that play a big part in how serious or how mild the condition develops in individual dogs.

Dermatomyositis can occur in humans as well as dogs, but it cannot be passed from one dog to another or one species to another. Puppies must be born with the gene to have the condition and they can only pass it on to offspring through reproduction. Most breeders spay and neuter puppies showing dermatomyositis as it is an inherited condition. They will also spay and neuter littermates as they are carrying the condition, just not showing the signs as obviously.

Typically owners will first notice lesions and red, irritated patches of skin on the head and muzzle when the puppy is under six months of age. Often the ears and around the eyes are the worse areas. The skin becomes raised and bumpy with hair loss on and surrounding the lesion. As the condition progresses the lesions will start to weep and a crusty coating will form over the irritated skin. Exposure to the sun and scratching will make the condition much worse and will often make the lesions deeper and more likely to scar. These lesions may spread to other locations in the body including the legs and elbows, tip of the tail and the toes. In mild cases the condition will often clear itself up in a few weeks, with hair growing back eventually. In severe cases the skin will scar deeply, resulting in bald patches of scarred skin that will be evident for life. When the disease begins to affect the muscles of the face the dog or puppy may have trouble eating and may have some malformation of the jaws as the muscles gradually atrophy. With very severe cases the dogs will come weak in the legs and will soon loose the ability to walk, eat or drink.

There is no cure for the condition once it has reached the point of affecting the muscles, however corticosteriods can be used to manage moderate flare-ups of the condition. Antibacterial creams to treat the lesions and protection from the sun's UV rays will also help in reducing the skin problems. With very severely affected dogs the only option may be to have the dog put down.