Canine Dermatomyositis

Canine familial dermatomyositis (DM) is seen primarily in Collies and Shetland Sheepdogs, but also reported in other breeds. This is an inheritable inflammatory disease affecting skin and muscle. The cause is unknown. Autoimmune problems and viral and/or bacterial infections in conjunction with hereditary predisposition have been suggested for DM in humans.

Signs of Canine Dermatomyositis

Signs include extensive alopecia, crusting, and inflammation on the face; hyper- or hypopigmentation; erosion and ulceration of the skin. Scarring may or may not be apparent clinically. Lesions of skin and muscle vary in severity. These signs may develop as early as at 6 months of age. Bony prominences, especially on the muzzle and around the eyes and ears are favored areas for the development of early lesions. Later, paws and tip of the tails may be affected, followed by inflammation of the paw pads. Inflammation of the claw bed may lead to claw degeneration. Pain and itching may follow if ulceration develops.

Muscle involvement is usually subtle in nature and may be limited to atrophy of certain facial muscles, with subsequent difficulties in chewing and swallowing.

Severely affected dogs show growth retardation, enlargement of the esophagus (resulting in chronic regurgitation), lameness, stiff gait and muscle degeneration. Infertility is an additional feature of severe DM.

Diagnosis of Canine Dermatomyositis

Canine familial dermatomyositis is characterized by signs which are similar to demodicosis and dermatophytosis, especially in young dogs. Skin scraping are usually performed to rule out demodicosis, and fungal culture is performed to rule out dermatophytosis. Electromyography (EMG) —examination of the electrical activity of the muscles and associated nerves—is used to confirm the DM.

Affected animals should not be bred, in order to prevent propagation of the underlying heritable disorder.

Treatment of Canine Dermatomyositis

Although corticosteroids have been used, the results are variable. Mildly affected young dogs may improve without any treatment.

Prognosis for Canine Dermatomyositis

The prognosis is usually fair. In some dogs, staphylococcal infections may develop. These dogs should be housed away from their litter mates. Systemic antibiotics and antimicrobial baths should be used to treat the infection. Severely affected dogs experience cyclic recurrences over their lifetime.

References:
1. Uc Davis Book of Dogs: The Complete Medical Reference Guide for Dogs and Puppies
2. Skin Diseases Of The Dog And Cat: Clinical and Histopathologic Diagnosis By Emily J. Walder, Verena K. Affolter, Peter J. Ihrke, Thelma Lee Gross
3. Small Animal Medical Therapeutics by Larry M. Cornelius, Duncan C. Ferguson, Michael D. Lorenz