By Dial A Vet Veterinary Team
Last updated: 2 November 2026
Crusty, hairless patches on a young Sheltie's or Collie's face, ears or tail tip are easy to mistake for mange or ringworm. Sometimes they are a sign of dermatomyositis, an inherited inflammatory disease of the skin and, in some dogs, the muscles. Most affected dogs have mild disease, but severe cases can affect eating, swallowing and breathing, so an accurate diagnosis matters.
Key takeaways
- Dermatomyositis is a hereditary inflammatory disease of the skin and muscle, seen mostly in Collies, Shetland Sheepdogs and their crosses.
- Signs usually start before 6 months of age, although adult onset can occur.
- Typical lesions are redness, scaling, crusting, sores and hair loss on the muzzle, around the eyes, ear edges, legs, feet and tail tip.
- Itch and pain are generally not features unless a secondary skin infection develops.
- A skin biopsy is needed to confirm the diagnosis.
- There is no cure, but many dogs are managed well. Avoiding sunlight and skin trauma is part of every plan.
What is dermatomyositis?
The University of Minnesota's Small and Large Animal Dermatology Handbook describes familial dermatomyositis as a hereditary inflammatory disease of the skin and muscle. It belongs to a group of conditions called ischaemic dermatopathies, where reduced blood supply damages the skin. Similar disease has been reported in Beauceron Shepherds, Belgian Tervurens and Portuguese Water Dogs, and a dermatomyositis-like disease is seen in other breeds.
The UC Davis Veterinary Genetics Laboratory describes it as an immune-mediated disorder with complex inheritance, caused by a mix of genetic and environmental factors.
Signs to watch for
Skin signs, as described by the Minnesota handbook and UC Davis, include:
- Redness, scaling and mild crusting at first
- Sores (erosions or ulcers) under the crusts
- Hair loss that can scar, with darker or paler skin
- Lesions on the top of the muzzle, around the eyes, on the ear edges, over the wrists and hocks, on the toes and at the tail tip
- Nail abnormalities in some dogs
Lesions often wax and wane, and mild cases can resolve on their own. Muscle problems usually follow the skin changes and tend to be worse in dogs with more severe skin disease. You may notice:
- Thinning of the chewing muscles on the head
- Thinning of muscles in the lower legs, or an abnormal gait
- Difficulty eating, drinking or swallowing in severe cases
The Minnesota handbook notes that some severely affected dogs develop megaoesophagus (an enlarged, floppy food pipe), and PetMD notes these dogs may develop pneumonia.
When to see a vet
Take your dog to your nearest vet clinic immediately if:
- Your dog is coughing, breathing fast or struggling to breathe
- Your dog keeps bringing food or water back up soon after swallowing
- Your dog cannot eat or drink
These can point to megaoesophagus and aspiration pneumonia, which need urgent care.
Book a vet visit soon if your puppy or young dog develops crusts, sores or hair loss on the face, ears, legs or tail tip, or seems to be losing muscle on the head. Many other conditions, such as mange, ringworm and bacterial infection, can look similar and need different treatment.
How vets diagnose it
Your vet may suspect dermatomyositis based on breed, age and where the lesions are. The Minnesota handbook explains:
- Other conditions such as demodectic mange, ringworm, bacterial skin infection and discoid lupus should be ruled out
- A skin biopsy is required to confirm the diagnosis
- A muscle biopsy or electromyography (EMG) can show muscle involvement but is not routinely done
- Blood tests may be used in some cases
Treatment and management
There is no cure, and treatment is tailored by your vet to how severe the disease is. According to the Minnesota handbook:
- Mild cases may only need supportive supplements, which your vet can advise on
- Moderate to severe cases may need medicines that calm the immune system or improve blood flow to the skin
- Secondary skin infections are treated as they arise
- Dogs with megaoesophagus may need feeding changes and close monitoring
PetMD notes most dogs can be treated as outpatients, but those with severe muscle inflammation and megaoesophagus may need hospital care. In the most severe cases, quality of life becomes the main concern.
At home:
- Limit sun exposure, as sunlight worsens lesions. Walk early or late and keep your dog indoors in the middle of the day
- Avoid rough play, tight collars and anything that rubs or injures the skin
- Use only shampoos and products your vet recommends
- Keep regular check-ups so treatment can be adjusted
Breeding and DNA testing
UC Davis explains that a 2017 study identified three genetic regions linked to risk in Collies and Shetland Sheepdogs, and a DNA test can estimate whether a dog is at low, moderate or high risk. Breeders can use the result to choose mating pairs that avoid producing high-risk puppies. The Minnesota handbook advises that affected dogs should not be bred. A low-risk result does not guarantee a dog will never develop skin disease, so any new lesions still need a vet check.
FAQ
Is dermatomyositis contagious?
No. It is an inherited immune-mediated disease, not an infection.
Is it itchy?
Itch is generally not a feature. If your dog becomes itchy, a secondary infection may be present.
Will my dog get worse with age?
The course varies. Lesions often wax and wane, and mild cases may resolve on their own, while severe cases need lifelong management.
Can other breeds get it?
Similar disease is reported in several other breeds, so a biopsy is important whatever the breed.
Talk with a vet
If your young dog has crusts or hair loss on the face, ears or tail, Dial A Vet's real vets and vet nurses can look at the skin with you on a video consult and help you plan next steps with your local clinic. You may also want to read about polymyositis in dogs. Book a video consult with Dial A Vet.
References
- University of Minnesota. Familial Canine Dermatomyositis. Small and Large Animal Dermatology Handbook, Vol. 3.
- UC Davis Veterinary Genetics Laboratory. Susceptibility to Dermatomyositis (DMS).
- PetMD Editorial. Inflammation of the Skin, Muscle, and Blood Vessels in Dogs. PetMD.
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If you are worried about your pet right now, contact your local vet or nearest emergency animal hospital.