Dermatomyositis

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Dermatomysositis in a Collie dog[1]

Dermatomyositis is an idiopathic immune-mediated skin disease characterized by inflammation of skin, connective tissue and underlying skeletal muscle[2].

This condition is most commonly found in the Collie and Shetland Sheepdog[3]. Breeding trials conducted in collie dogs suggest a dominant mode of inheritance. Although immunologic mechanisms have been proposed for the pathogenesis of canine dermatomyositis, the etiology is unknown[4].

In young dogs with familial dermatomyositis, skin lesions typically develop first with variable myopathies occurring later, similar to what is observed with human dermatomyositis. Lesions are characterized by papules, vesicles, pustules, and focal alopecia of the face, ears, tail, and extremities[5].

Ulcerative dermatosis may be a variant of this condition. occurring in middle-aged to older dogs as blisters and crusting in the inguinal and axilla regions.

Diagnosis usually requires skin biopsy to confirm a suspicion. The most consistent cutaneous histologic features of dermatomyositis are an inflammatory alopecia characterized by follicular atrophy and perifollicular inflammation[6].

Biochemical levels of creatine kinase and aspartate aminotransferase are generally elevated in affected dogs and electromyographic abnormalities.

In young dogs affected by this condition, fatal secondary amyloidosis may occur[7].

A differential diagnosis would include lupus erythematosus, where dermatomyositis is a histological feature of the disease[8] and nasal parakeratosis.

Other skin diseases which could be confused with this condition are erythema multiforme[9], bacterial pyoderma, pemphigus foliaceus, systemic lupus erythematosus, zinc-responsive dermatosis, vitamin A–responsive dermatosis, toxic epidermal necrolysis and drug eruptions.

Although steroids such as oral prednisolone may induce a measure of clinical improvement, treatment of familial dermatomyositis has been partially successful with oral pentoxifylline at 25 mg/kg twice daily for 3 months[10].

References

  1. Illinois Sheltie Rescue
  2. Scott, DW et al (1995) Muller and Kirk's Small Animal Dermatology. W.B. Saunders Co., Toronto. pp:759-765
  3. Clark LA et al (2005) Linkage of dermatomyositis in the Shetland Sheepdog to chromosome 35. Vet Dermatol 16(6):392-394
  4. Hargis AM et al (1984) Familial canine dermatomyositis. Am J Pathol 116:234
  5. Ferguson EA et al (2000) Dermatomyositis in five Shetland sheepdogs in the United Kingdom. Vet Rec 146(8):214-217
  6. Gross TL & Kunkle GA (1987) The cutaneous histology of dermatomyositis in collie dogs. Vet Pathol 24(1):11-15
  7. Hargis AM et al (1989) Severe secondary amyloidosis in a dog with dermatomyositis. J Comp Pathol 100(4):427-433
  8. Jackson HA & Olivry T (2001) Ulcerative dermatosis of the Shetland sheepdog and rough collie dog may represent a novel vesicular variant of cutaneous lupus erythematosus. Vet Dermatol 12(1):19-27
  9. Kimmel SE et al (2003) Clinicopathological, ultrasonographic, and histopathological findings of superficial necrolytic dermatitis with hepatopathy in a cat. JAAHA 39:23–27
  10. Rees CA & Boothe DM (2003) Therapeutic response to pentoxifylline and its active metabolites in dogs with familial canine dermatomyositis. Vet Ther 4(3):234-241