Dermatomyositis (DMS)

When Does It Appear?

Signs often begin in puppies, sometimes from approximately seven to twelve weeks of age, but DMS can also first appear in an adult dog. Earlier onset is often associated with more genetic risk variants and may be more severe.

DMS is a complex disease. Genetic susceptibility is important, but not every genetically at-risk dog develops clinical signs. Environmental or immune triggers may influence whether and when the condition appears.

Possible Signs

Skin signs

• Hair loss, scaling, crusting or sores on the face and ear tips
• Lesions around the eyes or on the lips and muzzle
• Lesions on the feet, legs, tail tip and bony prominences
• Scarring or changes in skin colour as lesions heal

Muscle signs

• Muscle wasting, particularly around the head and jaw
• Weakness or a stiff, high-stepping gait
• Difficulty eating, drinking or swallowing
• Regurgitation or aspiration associated with oesophageal weakness

Mild cases may involve skin lesions only. Muscle involvement is reported more commonly in Collies than in Shetland Sheepdogs.

Treatment and Management

There is no single cure. Treatment is selected according to the severity of the skin and muscle disease and may include medication to improve blood flow or control inflammation and immune activity. Vitamin E or other supportive treatment may also be recommended.

Dogs should be protected from strong ultraviolet light and from activities that repeatedly damage affected skin. Secondary infection, pain and swallowing difficulties must be treated promptly.

Never begin prednisone, ciclosporin, azathioprine, pentoxifylline or another medicine without veterinary supervision. Some treatments require blood monitoring and may not be suitable for every dog.

The outlook varies. Mild juvenile cases may improve as the dog matures, although scarring can remain. Severe muscle or swallowing involvement can be life-threatening and requires specialist care.

Understanding the Genetic Test

The DMS test assesses variants at three loci associated with disease risk in Collies and Shetland Sheepdogs:

• Locus A: a variant in the PAN2 gene
• Locus B: a variant in the MAP3K7CL gene
• Locus C: the DLA-DRB1*002:01 risk haplotype

Capital letters represent identified risk alleles; lower-case letters represent the alternative alleles. The result estimates genetic risk and does not state with certainty whether a dog will develop DMS.

Laboratories may refine their interpretation as more dogs are tested, so the current report and guidance issued by the testing laboratory should always be used.

Current Risk Groups

Breeding Considerations

DMS testing is a risk-management tool, not a simple clear-or-affected test. Breeders can use the results to avoid combinations expected to produce high-risk puppies while preserving genetic diversity.

Results for both proposed parents should be considered together. Dogs should not be selected or excluded on the DMS result alone. Health, temperament, conformation, pedigree diversity and the laboratory’s current breeding guidance also matter.