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Autoimmune and Immune‐Mediated Skin Diseases

Nicole A. Heinrich, DVM, DACVD

McKeever Dermatology Clinics, Eden Prairie, MN, USA

Canine Familial Dermatomyositis may rarely occur in chronically affected dogs. Minimally
affected dogs may experience spontaneous resolution of
Dermatomyositis (DM) is a hereditary, ischemic der- skin lesions while other dogs may require lifelong therapy.
matopathy and myopathy that occurs most commonly in
collies, Shetland sheepdogs, Beauceron shepherds,
Belgian tervurens, and Portuguese water dogs. Affected Erythema Multiforme
dogs generally develop lesions when they are less than
6 months of age, and either sex can be affected. Erythema multiforme (EM) is an inflammatory cutane-
Dermatomyositis is characterized by nonpruritic ous reaction pattern of multifactorial etiology, and dogs
alopecia, erythema, scaling, and mild crusting of the face, and cats of any age, breed or sex may be affected. It is
ears, distal limbs, digits, tail, and bony prominences characterized by rarely pruritic, sometimes painful, ery-
(Figure 162.1). Additionally, claws may slough and frag- thematous macules or papules that coalesce and eventu-
ment and ulceration may be rarely present in the oral ally form a clear center and acquire an annular to
cavity. Skin lesions may vary in severity depending on the arciform shape. Additional skin lesions may include
individual. The presence and degree of myositis also vary. plaques, vesicles and bullae, ulcers, and urticaria. Classic
Clinical signs of myositis include regurgitation associ- target lesions are present in only about one‐third of
ated with megaesophagus, a high‐stepping stiff gait, and cases. The axillae, groin, mucocutaneous junctions,
atrophy of the masticatory muscles and distal limbs. pinnae, and footpads are most frequently affected. Oral
The diagnosis of DM is made through history, physical ulceration may be present in some cases. Erythema
examination, and skin biopsy. Punch biopsies should be multiforme can be classified into various categories
taken from the center of an alopecic area of skin. Crusted based upon severity; however, such classifications are
lesions can also be biopsied. The skin should not be beyond the scope of this chapter.
scrubbed or clipped prior to procuring the biopsy. Care The disease is diagnosed based on history, physical
should be taken to include only abnormal skin in the examination, and skin biopsy findings. Punch biopsies
biopsy. Histopathology will feature changes characteris- should be taken from the center of an erythematous area
tic of ischemic dermatopathy. of skin. The clinician should biopsy affected skin and avoid
Benign neglect may be an appropriate treatment ulcerated areas as ulcerated skin may yield a nondiagnos-
approach for minimally affected patients. Avoidance of tic sample. The skin should not be scrubbed or clipped
trauma to bony prominences and avoidance of prolonged prior to procuring the biopsy. Care should be taken to
sun exposure may also be beneficial. Pentoxifylline, include only abnormal skin in the biopsy. Histopathology
prednisone, vitamin E, omega‐3 fatty acids, tetracycline reveals apoptosis of keratinocytes at various levels of the
with niacinamide, and topical tacrolimus are therapies epidermis combined with lymphocyte satellitosis.
that may be used either alone or in combination depend- Erythema multiforme has a variable appearance, and
ing on patient response (Table 162.1). therefore many potential clinical differentials. Some
Complications can include secondary pyoderma for differential diagnoses include systemic lupus erythema-
those dogs with more significant skin lesions and aspiration tosus, urticaria, superficial pyoderma, dermatophytosis,
pneumonia for those with megaesophagus. Amyloidosis demodicosis, bullous autoimmune disease, vasculitis

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical