Dermatomyositis in Dogs
Dermatomyositis is an inherited inflammatory disease of the skin, muscles, and blood vessels. It typically develops in young collies, Shetland sheepdogs, and their crossbreeds. Similar symptoms have been reported in other breeds, such as the Beauceron Shepherd, Welsh Corgi, Lakeland terrier, Chow Chow, German Shepherd, and Kuvasz, as well as individual dogs. However, the condition in these dogs currently is classified as ischemic dermatopathy (low blood supply to the skin) and not dermatomyositis as previously reported. Studies suggest that dermatomyositis is inherited in an autosomal dominant manner (the chromosome is inherited from both parents), with variable expression. Skin lesions typically develop before six months of age, and may develop as early as seven weeks. The full extent of lesions usually is present by one year of age, with lessening afflictions thereafter. Adult-onset dermatomyositis can occur, but it is rare.
Symptoms and Types
Signs of dermatomyositis can vary from subtle skin lesions and inflammation of muscles, to severe skin lesions and a generalized decrease in muscle mass (known as muscle atrophy), with an enlarged esophagus (the tube running from the throat to the stomach). Skin lesions around the eyes, lips, face, and inner surface of the prick ears will vary in intensity; the entire face may be involved. The tip of the tail and bony prominences can also be affected.
Lesions may increase and decrease over time. They are characterized by variable degrees of crusted areas, with loss of the top surface of the skin (they are referred to as erosions or ulcers, based on the depth of tissue loss) and alopecia. Reddening of the skin (erythema), and accumulations of surface skin cells, such as seen in dandruff, or scaling skin, may be manifestations of this disease. The initial skin lesions may leave scars on the skin. More severely affected dogs may have difficulty eating, drinking, and swallowing.
Symptoms of dermatomyositis are usually seen in affected dogs before they are six months of age. Several litter-mates may be affected, but the severity of the disease often varies significantly among dogs that are affected by this disease. Foot-pad ulcers and ulcers in the mouth as well as nail abnormalities or loss may occur, along with inflammation of the muscles. Signs may be absent, or they may vary from a subtle decrease in the mass of the muscles extending from the top and side of the head, behind the eye, to the lower jaw, or they may be too generalized, with loss of muscle mass at equal points of the body. A stiff gait may also be present. There will often be a decrease in muscle mass of the muscles extending from the bone below the eye to the lower jaw muscle that acts to close the jaw, and in the muscles extending from the top and side of the head and behind the eye, to the lower jaw muscles that act to close the jaw. Dogs that have been diagnosed with an enlarged esophagus may come down with pneumonia. Conditions that can lead to pneumonia will need to be avoided.
Causes for dermatomyositis can usually be traced to a hereditary source, but can also be sourced to an immune-mediated disease, or to infectious agents.