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246.e2 Dermatomyositis

Dermatomyositis
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and lameness. Undetected but affected females
BASIC INFORMATION
may have infertility problems. • Cutaneous pain is prevalent in Beauceron
shepherds.
Definition • Myositis usually occurs after skin lesions
Familial canine dermatomyositis is a hereditary, Clinical Presentation develop, and severity correlates with skin
idiopathic inflammatory skin and muscle disease HISTORY, CHIEF COMPLAINT lesion severity.
of several dog breeds that is characterized by • Young dog presenting with hair loss and
alopecia, erosions, and crusting, predominantly scaling on ear tips, face, pinnae, bony Etiology and Pathophysiology
over bony prominences, tip of the tail, and prominences, and tip of tail • Autosomal dominant mode of inheritance
pinnae. • Puppies may be painful or inappetent, the with variable expression
latter being directly related to the degree of • Immune-mediated or autoimmune basis
Epidemiology myositis affecting pharyngeal muscles. but it is unclear if an immune reaction
SPECIES, AGE, SEX is the cause of the disease or occurs in
• Dogs: primarily young dogs (<6 months old), PHYSICAL EXAM FINDINGS response to pre-existing muscle or skin
some as early as 7-11 weeks of age. Lesions • Clinical signs wax and wane and vary from damage.
usually noted by 1 year of age minor skin lesions (papules/rarely vesicles) • Lesions can be induced by drugs, vac-
• Cats: not reported to severe ulceration of the skin, with a cines, infection (especially viral), toxins,
generalized debilitating myositis affecting internal disease, but causal relationship is
GENETICS, BREED PREDISPOSITION the head and distal limbs. unproved.
• Familial basis shown in collies, Shetland • Skin lesions are characterized by erosion and
sheepdogs, Beauceron shepherds, Belgian crusting around the eyes, on the bridge of the DIAGNOSIS
Tervurens, Portuguese water dogs, Kelpies nose, lips, ears, bony prominences (elbows,
• Acquired disease has been reported in many hocks, digits), and the tail tip. Vesicles are Diagnostic Overview
other breeds: mongrel, Welsh corgis, Lake- occasionally noted. Pediatric patients presenting with hair loss and
land terrier, chow chow, German shepherd, • Pruritus is not normally present unless compli- crusting on face, ear tips, and tail tip along
kuvasz, and Australian cattle dog cated by another condition such as pyoderma. with muscle wasting in a predisposed breed
• Some dogs present with onychodystrophy (e.g., collie, Shetland sheepdog) is highly
RISK FACTORS (abnormal claw formation). Ulcers of the suggestive.
Mechanical trauma, sunlight (UV), and repro- footpads are rarely noted.
ductive stress (estrus, parturition, lactation) may • Healing may lead to scarring alopecia. Differential Diagnosis
worsen the lesions. • Megaesophagus and aspiration pneumonia • Demodicosis
are occasionally noted. • Dermatophytosis
ASSOCIATED DISORDERS • Stunted growth, lameness, and muscle • Bacterial folliculitis
Myositis and muscle atrophy may lead to wasting may occur as the disease progresses. • Malassezia dermatitis
dysphagia, megaesophagus with subsequent • Littermates may be affected to different • Discoid lupus erythematosus
aspiration pneumonia, skeletal muscle weakness, degrees. • Vasculitis

DERMATOMYOSITIS Abnormal electromyogram for a dog with dermatomyositis. Interosseous muscle (right).

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