What is familial dermatomyositis in dogs?
Familial dermatomyositis is an inherited inflammatory disease characterized by joint damage to the skin and muscles.
The Collie, Shetland Shepherd, Beauceron, Australian Shepherd, German Shepherd, Chow-Chow, or Welsh Corgi breeds seem to be predisposed to it.
In the Collie, the disease would be transmitted according to an autosomal dominant mode with variable expressiveness. In other words, the gene responsible for the disease would be carried by a non-sex chromosome and it would only take one copy of the gene carrying the anomaly, transmitted by a sick parent, for the dog to be affected by the disease. .
However, the genetic factor does not seem to be the only triggering factor for the disease. Other factors such as viral, immune/allergic, traumatic causes or ultraviolet rays could also play a role in its appearance.
How does the disease manifest in dogs?
In dogs, as in humans who can also be affected by this disease, the symptoms of dermatomyositis are very variable.
Clinical signs include both skin signs and muscle signs. While some animals show both, some may show only one or the other of these symptoms.
The cutaneous signs of the disease generally appear first and very early in the dog's life, between the ages of 7 weeks and 6 months. They are typically followed by muscle signs in the months that follow. More rarely, the signs can only occur in adulthood and coincide with the heat period, gestation, lactation, prolonged exposure to sunlight or trauma.
Skin damage usually begins on the dog's face, around his eyes and lips, on the nose, at the end of the ear flaps, on the tip of the tail and/or at the end of the legs .
In severe forms, bony prominences such as the shoulders, elbows, knees, tarsi and carpi may show lesions.
These lesions consist of depigmentation, erythema (redness of the skin), papules (kinds of pimples), ulcers that form crusts and give way to hairless scars.
Vesicles and ulcers may appear on the oral mucosa although this is rare.
The lesions can be complicated by a secondary infection that causes itching.
Muscular symptoms usually occur a few weeks to a few months after skin symptoms.They may consist of atrophy of the masseters (jaw muscles), stiffness of gait, exercise intolerance as well as swallowing disorders and regurgitation related to a megaesophagus.
How is this disease diagnosed?
The veterinarian can suspect the disease by observing the clinical signs presented by the dog, depending on its breed and age.
But the definitive diagnosis of this disease is based on skin and muscle biopsies, electromyography and a dosage of circulating immune complexes.
How can canine familial dermatomyositis in dogs be treated?
The treatment is essentially medical and depends on the severity of the symptoms. It only limits the symptoms of the disease and uses immunosuppressive drugs, antibiotics in the event of associated superinfection and the use of antiseptic or keratoregulating shampoos.Administration of essential fatty acids and vitamin E may also be beneficial.