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Abstract. In this study, 50 cases of canine pemphigus foliaceus and 49 cases of canine superficial pyoderma were examined by immunohistochemical staining for patterns of desmoglein expression. In 31/50 (62%) of pemphigus foliaceus cases, there was an altered staining pattern for desmoglein consisting of distinct clumped deposits at the periphery of keratinocytes and/or dark cytoplasmic staining of acantholytic cells (consistent with internalization of desmoglein). In contrast, desmoglein staining in biopsies from cases of superficial pyoderma was diffusely pale without evidence for clumping or distinct internalization. This study demonstrates that epidermal desmoglein expression is altered in some cases of pemphigus foliaceus in dogs and suggests that immunohistochemical staining for this protein may be useful in diagnosis.Pemphigus foliaceus is an autoimmune skin disease (AISD) of people and animals characterized by lack of adhesion between keratinocytes (acantholysis) and intraepidermal vesicle or pustule formation. 9 In 77% of dogs with pemphigus foliaceus, antikeratinocyte antibodies can be demonstrated. 9 The target antigen is a desmosomal transmembrane glycoprotein, desmoglein 1, of the cadherin family of intercellular adhesion molecules. 6,11 The diagnosis of pemphigus foliaceus in dogs relies on multiple criteria including clinical signs, distribution of lesions, histopathology, and immunohistochemistry. Immunohistochemical staining for immunoglobulin and complement components may not distinguish pemphigus foliaceus from superficial pyoderma associated with bacterial infections, as similar deposition patterns may occur. 8,9 Immunohistochemical staining for desmoglein 1 has been used to demonstrate an altered pattern of desmoglein expression in lesional and perilesional skin from people with pemphigus foliaceus. In skin from healthy individuals, desmoglein 1 occurs in an evenly distributed, finely stippled pattern at the periphery of keratinocytes. [2][3][4]12 In contrast, both lesional and nonlesional skin from pemphigus foliaceus patients may have patchy pericytoplasmic staining coupled with cytoplasmic staining of acantholytic cells. [2][3][4] From the Departments of Veterinary Pathology (Steeves, Clark) and Veterinary Microbiology (Chelak, Haines), Western College of Veterinary Medicine, 52 Campus Drive, University of Saskatchewan,

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