General Considerations

1. Pemphigus foliaceus, pemphigus erythematosus, and pemphigus vulgaris are common to rare autoimmune skin disorders of dogs and cats.
2. Antibodies (usually IgG) are directed against components of an epidermal intercellular structure that holds the cells together called desmosomes. These include desmocolin 1 or desmoglein 1 (pemphigus foliaceus) and desmoglein 3 (pemphigus vulgaris). Desmocollin-1 was recognized as the major autoantigen in canine pemphigus foliaceus. The binding of the antibodies to these molecules cause the ultimate release of enzymes (plasminogen activator/plasmin) that degrade the desmosomal components resulting in acantholysis, which is the release of inter-cellular attachments allowing the cell to float and round-up.
3. Microscopically, acantholytic keratinocytes are large, purple, fried-egg resembling cells. They are immature detached keratinocytes and represent the hallmark of pemphigus diseases. These cells can also be seen in severe suppurative skin disorders (e.g. pyoderma) and in dermatophytosis typically caused by Trichophyton mentagrophytes organisms. Be aware that dermatophytosis caused by T. mentagrophytes can mimic pemphigus foliaceus clinically and histologically. However, this pustular form of dermatophytosis is rare.
4. Forms of pemphigus:
   1. Superficial – Pustules are formed underneath the stratum corneum or inside the stratum granulosum. Therefore, superficially in the epidermis.
      1. Pemphigus foliaceus.
      2. Pemphigus erythematosus.
   2. Deep – Pustules are formed just above the basal cell layer. Therefore, deeply in the epidermis.
      1. Pemphigus vulgaris.
5. Pemphigus-like adverse cutaneous reactions may be triggered by drugs, most commonly antibiotics including cehalosporins and penicillins, and topical flea and tick control medications containing dinotefuran, pyriproxyfen, and permethrin (Vectra 3D®) and fipronil, amitraz, and S-methoprene (Certifect®). Clinical signs typically mimic pemphigus foliaceus.
6. There is also controversy that pemphigus may occur as a sequel to chronic inflammatory skin diseases.
7. Secondary skin and ear infections can occur in any form of pemphigus and they should be identified and treated.