How should pemphigus foliaceus be diagnosed and managed in dogs?

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Pemphigus foliaceus (PF) is diagnosed by histopathology confirming subcorneal pustular dermatitis with acantholytic keratinocytes, and managed with long-term systemic immunosuppression — typically glucocorticoids as the foundation, with adjunctive agents added for refractory or severe disease. Diagnosis begins with cytology and is confirmed by biopsy. Cytology of intact pustules reveals rounded acantholytic epithelial cells with nuclei and basophilic cytoplasm, along with neutrophils and rarely eosinophils.3 Histopathology is the gold standard, demonstrating subcorneal pustules containing rafts of or individualized acantholytic cells.8 The biopsy site should not be scrubbed prior to sampling — clipping the hair is permissible, but scrubbing disrupts the diagnostic lesion.8 Direct immunofluorescence detects tissue-bound autoantibodies and supports the diagnosis; indirect immunohistochemistry demonstrating IgG-positive staining around keratinocytes is an alternative.3 In dogs with concurrent immune-mediated thrombocytopenia (IMT), platelet surface-associated immunoglobulin detected by flow cytometry confirms the hematologic comorbidity.6 Lesion distribution guides clinical suspicion. Canine PF classically affects the trunk, ears, and face, with pustules that rapidly progress to crusts and erosions.3 Footpad-dominant and mucocutaneous junction involvement occurs but is less common.3 Lesions on constantly traumatized surfaces such as footpads are dominated by crusting rather than intact pustules due to easy rupture from friction.3 Bilateral symmetry is characteristic.9 Systemic signs including fever are possible, particularly when concurrent vasculitis or hematologic autoimmune disease is present.56 First-line treatment is systemic glucocorticoids at immunosuppressive doses. Prednisone or prednisolone is the recommended initial therapy.1 Dogs with concurrent overt vasculitis take a median of 93.8 days to achieve remission, compared with 41.8 days in dogs without vasculo