Heading into the unknown: autoimmune skin disorders (Proceedings)

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Heading into the unknown: autoimmune skin disorders (Proceedings)


The autoimmune skin disorders are a group of confusingly similar diseases. In this section the most common autoimmune skin diseases will be presented and they will be discussed from a clinical perspective. Most of the autoimmune skin diseases are treated similarly and this will be discussed in the last part of this section.

Clinical Presentation

Autoimmune skin diseases show great variation in cutaneous lesions; however, certain lesion patterns are consistently observed that include crusts, erosions, ulcers along with pustules, vesicles, bullae, and papules.

• Face - nasal planum, ear pinnae
• Foot pads
• Mucous membranes - oral, ocular, genital

Pemphigus Complex

Pathogenesis

Autoantibodies (usually IgG) are directed against components of the epidermal cell membrane responsible for cellular adhesion (desmoglein). The binding of anti-desmoglein antibodies initiates cellular events that eventually degrade the desmosomal components (cellular attachments) and results in acantholysis (release of the cellular attachments allowing the cells to float, or roundup, with subsequent cleft formation). Acantholytic cells (big, purple, fried egg cells) are immature, detached, keratinocytes that are the hallmark of pemphigus diseases. This is considered a Type II (Antibody-dependent) reaction with antibodies directed against tissue-bound antigens.

Pemphigus Foliaceus

• Most common autoimmune skin disease in small animals. Overrepresented in certain breeds, such as: Akitas, Chows, Dachshunds, Collies, ± Doberman Pinschers, Newfoundlands.
• Spontaneous form of the disease with no known cause.
• Drug/ tumor/ infection induced form - Some patients may have had chronic skin disease and thus have been exposed to many drugs in their past history.
     √ Lesions: Pustules and crusts that can wax and wane despite therapy
     √ Distribution: Nasal planum, pinnae, footpads, Can mimic pyoderma (pustules, crusts)
     √ ± pain/ pruritus - variable (not usually as pruritic as allergic patients).
     √ The pruritus is usually noted AFTER the development of crusted lesions, whereas an allergic patient is typically pruritic BEFORE the development of crusted lesions.
     √ Systemic signs uncommon
     √ Secondary pyoderma may be present, but the patient usually feels good
     √ Distribution may involve: Nasal planum - ± mucocutaneous junctions, Ear pinnae - not an otitis externa –lesions only affecting the pinnae, Footpads (hyperkeratotic) - may be the only sign.
     √ *oral mucosal involvement is usually not seen
     √ Diagnosis: Clinical signs- papules, pustules and crusts affecting primarily nasal planum, ear pinnae, foot pads
• Cytology - acantholytic cells, non-degenerate neutrophils; may observe bacteria (cocci)
• Histopathology - subcorneal vesicles or pustules containing acantholytic cells, neutrophils ± eosinophils
• CBC, Serum chemistries, UA – usually normal
• Occasionally some inflammatory changes will be present - hyperglobulinemia ± hypoalbuminemia, Leukocytosis due to neutrophilia. Antinuclear antibody test (ANA) - negative

Pemphigus Vulgaris

• No age, breed or sex predilections; rare disease with a very poor prognosis
• Oral lesions - High percentage of patients will present with oral lesions, often the chief complaint. Most severe form of because the lesions are deeper than those associated with Pemphigus foliaceus
• Primary lesions are rare - vesicles, bullae
• Secondary lesions are common - erosions, ulcers, crusts ± pain
• Deep lesions are painful and the secondary systemic signs are common due to the deep lesions and secondary infections (pyrexia, anorexia, depression).
• Sick animal on presentation
• Distribution may involve: nasal planum, ear pinnae, foot pads and the oral cavity (80% of cases)
• mucocutaneous junctions, claw folds, axillary and inguinal region—areas of friction especially.
• Diagnosis:Clinical signs - Erosions/ulcers affecting the nasal planum, ear pinnae, foot pads
• Oral lesions, mucocutaneous junctions along with axillary and inguinal areas
• Cytology - acantholytic cells, neutrophils, few bacteria
• Histopathology - suprabasilar vesicles or pustules containing acantholytic cells, neutrophils ± eosinophils
• CBC, Serum chemistries, UA, ANA - usually inflammatory changes associated with secondary infection; ANA - negative