What is dermatomyositis?
Dermatomyositis is an inherited disease of the skin, muscles, and blood vessels that causes dramatic inflammation of these tissues in the body. The affected breeds are Collies, Shetland Sheepdogs, and dogs that are mixes of these breeds. In dogs with this genetic trait in their DNA, the expression of this disease is variable. While the exact pathologic mechanisms of dermatomyositis are unknown, an immune-mediated process may be involved.
Other breeds that have been reported with signs similar to the dermatomyositis(dermatomyositis-like disease) seen in Collies and Shelties include:
- Welsh Corgi
- Lakeland Terrier
- Chow Chow
- German Shepherd
Dermatomyositis is considered a disease of the young, as lesions usually develop before 6 months of age, and may emerge as early as 7 weeks of age. The worst of the lesions are typically present by a year of age. Adult-onset dermatomyositis is rare.
"Clinical signs can vary greatly from very subtle skin lesions and muscle inflammation to quite severe skin ulcerations and loss of muscle mass"
Clinical signs can vary greatly from very subtle skin lesions and muscle inflammation to quite severe skin ulcerations and loss of muscle mass (atrophy). The skin lesions may be crusty erosions, areas of hair loss, or actual ulcers, and they tend to occur around the eyes and lips, on the face, on the ear flaps, or on the tip of the tail. It is not uncommon for the skin lesions to wax and wane over time. Oral ulcers may develop, and the foot pads and nail beds can also be affected. Ultimately, scarring may develop in the affected areas. If the chewing muscles are affected and develop scarring, the dog may develop difficulty eating, drinking, or swallowing. Severely affected individuals develop a stiff or “goose-step” gait. The esophagus, which carries food from the mouth to the stomach, may dilate causing regurgitation, weight loss, and loss of condition, and pneumonia from aspiration of food or liquid. Dermatomyositis is best diagnosed by biopsy of affected skin and/or muscle.
How is dermatomyositis treated?
Dermatomyositis is best considered a condition that is managed rather than cured. Most dogs with dermatomyositis can be managed at home, rather than in the hospital. It is important to avoid activities that could traumatize the skin or muscles of affected dogs. Ultraviolet light exposure may worsen skin lesions, so it is important to be mindful of the time these dogs spend outdoors.
"Dermatomyositis is best considered a condition that is managed rather than cured."
If the chewing muscles are affected, the dog may need assistance eating such as hand feeding or forming softened food into “meatballs”. For dogs with an enlarged esophagus, food consistency and feeding patterns may need to change. Your veterinarian will be able to work through the details with you, individualized to the specific dog’s issues.
Some dogs need non-specific symptom control with hypoallergenic shampoos and treatment of secondary bacterial skin infections that may occur in the skin lesions. Essential fatty acids (EFAs) and vitamin E can help inmore mild cases. Tetracycline and niacinamide can be used to modulate the immune system, decreasing symptoms. Pentoxifylline can improve microcirculation in the skin resulting in resolution of skin lesions. Some dogs need anti-inflammatory medication such as cyclosporine (Atopica™) or in severe cases, a corticosteroid such as prednisone.. Tacrolimus ointment can be used topically on any active skin lesions. Use only medication prescribed by your veterinarian, and follow the instructions carefully.
What is the long-term outlook for dogs with dermatomyositis?
"The prognosis for dogs with dermatomyositis is highly variable and depends upon the severity of their disease."
The prognosis for dogs with dermatomyositis is highly variable and depends upon the severity of their disease. For dogs with mild disease, the outlook is excellent. Their disease tends to resolve on its own with no evidence of scarring in the skin or muscles. For dogs who are moderately affected, their symptoms may resolve spontaneously, but scarring is common. Severe disease may cause life-long inflammation in the skin and muscles, so euthanasia may be indicated.
Chronically affected dogs may be at increased risk for kidney disease, so it is important to have your pet monitored regularly.
While dermatomyositis is not curable, the course of the disease is quite variable, so only time and treatment will reveal how well an individual dog will do.