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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • An autoimmune skin disease and the most common cause in the author's practice for noninfectious crusts in the horse. It is also the most commonly seen autoimmune skin disease in the horse, after purpura haemorrhagica
  • The exact pathomechanism has not been investigated in the horse, but it is presumed to be similar to that for humans and the dog—autoantibodies are produced that attack the intercellular connections between the skin's epidermal cells. This leads to formation of transient pustules or bullae and subsequent crusts
  • Geographic distribution of the disease is presumably worldwide. The incidence is unknown but the disease is relatively uncommon. In California, 80% of the horses first exhibited signs between September and February. Skin and hemolymphatic system are affected.

Signalment!!navigator!!

  • Appaloosa were predisposed in 1 study
  • No sex predilection
  • The mean age of onset was 8.6 years with a range of 2.5 months to 25 years

Signs!!navigator!!

  • Crusts frequently start on the face and legs and become generalized
  • Occasionally, crusts only on the coronary band
  • Alopecia
  • Pustules
  • Urticaria
  • Peripheral edema (“stocking up”)
  • Lethargy, anorexia, pyrexia

Causes and Risk Factors!!navigator!!

Unknown in most cases. 1 published case—possibly caused by penicillin.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Severe superficial staphylococcal dermatitis
  • Dermatophytosis
  • Dermatophilosis
  • Sarcoidosis (chronic granulomatous disease)

CBC/Biochemistry/Urinalysis!!navigator!!

Low-grade anemia combined with a leukocytosis.

Other Laboratory Tests!!navigator!!

N/A

Imaging!!navigator!!

N/A

Other Diagnostic Procedures!!navigator!!

  • Skin biopsy for histopathology. Very important not to surgically prepare the area to be biopsied. It is acceptable to surgically prepare the site after taking the biopsy sample (i.e. before suturing the site) to limit chances of infection. Choose multiple sites, and include the crust. Provide the pathologist with the patient signalment, a brief history, descriptions and locations of the biopsied sites, as well as differential diagnosis
  • Cytology of aspirates or impression smears from pustules and crusts may reveal acantholytic cells and neutrophils
  • Bacteriologic and fungal (dermatophyte test medium) cultures will identify secondary bacterial folliculitis or dermatophytosis, respectively

Pathologic Findings!!navigator!!

  • Subcorneal or intracorneal pustules with acantholytic cells
  • Certain strains of the dermatophyte species Trichophyton may cause acantholysis; therefore, any histology suggestive of PF should have special stains for fungi performed

Treatment ⬆ ⬇

TREATMENT

  • Control disease, reduce lesions, return horse to function
  • May not be able to eliminate all lesions

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • CS at immunosuppressive doses (prednisolone 1 mg/kg every 12 h PO, dexamethasone 0.05–0.1 mg/kg every 24 h IM, PO, IV) for 2 weeks, then taper to lowest effective dose
  • Azathioprine in combination with the above CS at 1 mg/kg every 24 h PO for 1 month, then every 48 h. Expect 1 month for effect. Azathioprine is used as a steroid-sparing agent and is moderately expensive. As it takes effect, the CS dosage should be slowly reduced

Contraindications/Possible Interactions!!navigator!!

  • Horses with a predisposition to laminitis, or with a previous history of laminitis, should be monitored very closely for recurrence, or possibly just treated with azathioprine, although this method of treatment has not been substantiated in equine PF
  • Therapeutic precautions include the following—CS: laminitis; azathioprine: bone marrow suppression (rare)

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Physical examinations, especially looking for resolution of lesions as well as laminitis caused by CS
  • If initially anemic, monitor with hemogram
  • If using azathioprine, monitor hemogram and platelets, once monthly.

Prevention/Avoidance!!navigator!!

N/A

Possible Complications!!navigator!!

  • CS-induced laminitis
  • Immunosuppression can predispose animal to secondary cutaneous (pyoderma, dermatophytosis) and systemic infections, although rare

Expected Course and Prognosis!!navigator!!

  • Guarded to good, depending on response to treatment and if CS-induced adverse effects occur
  • Some horses need lifelong treatment, others may have treatment discontinued after complete resolution of lesions without the PF recurring
  • Advise client of the controllable, rather than curable, nature of the disease
  • In a minority of cases, it is possible to taper down and stop medication without relapse
  • Advise client of the adverse effects of medications

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Pregnancy/Fertility/Breeding!!navigator!!

  • Anecdotal reports of affected mares giving birth to affected newborn foals
  • 1 report describes a female donkey in which PF occurred, then regressed, during 2 of its 5 pregnancies

Abbreviations!!navigator!!

  • CS = corticosteroid
  • PF = pemphigus foliaceus

Suggested Reading ⬆ ⬇

Vandenabeele SIG, White SD, Kass P, et al. Pemphigus foliaceus in the horse: 20 cases. Vet Dermatol 2004;15:381–388.

Author(s) ⬆ ⬇

Author: Stephen D. White

Consulting Editor: Gwendolen Lorch

Additional Further Reading ⬆

Click here for Additional Further Reading