Dr Rick Last – Specialist Veterinary Pathologist
Pemphigus foliaceus (PF) is the most common feline autoimmune dermatosis. In cats lesions of PF are superficial pustules which, as the result of being thin roofed, frequently rupture to form crusts and underlying erosions. Lesion distribution is usually bilaterally symmetrical and most frequently involves nasal planum / muzzle, ear pinnae, nipples, ventral abdomen, nail (ungual) folds and footpad margins. Exudates on the feet can be quite severe and frequently lesions are restricted to the feet alone. PF has a mean age of onset at 6.1 years, no sex predeliction and in ± 80% of affected cats pruritis is observed. (Figures 1 – 7)
Pathophysiology of the condition involves autoantibody targeting the intercellular desmosomal proteins in the upper levels of the stratum corneum with resultant cell dissociation (acantholysis) with vesicle formation. Currently known triggers of PF in cats include genetic (spontaneous), drug induced, chronic disease associated and more recently sunlight exposure. Remember “drugs” include food colorants, preservatives, anti-oxidants and texture modifiers.
Cytology involves examination of smears prepared form pustule contents or crusts. Intact pustules provide the best diagnostic material, but are frequently not present in cats and so the yellow crust adhered to the eroded epidermis is most commonly examined. Newly erupted areas should be selected for sampling as these are less likely to be affected by bacterial colonization and self-trauma. Gently peel back crusts (pinnae and top of the head are good locations) to reveal shiny, sometimes blood tinged, eroded epidermis. Impression smears of the underside of the crust and eroded epidermis are made and stained with Diff-Quik® for examination. Cytology may provide a tentative diagnosis based on the presence of free lying or rafts of acantholytic keratinocytes intermingled among well preserved neutrophils and / or eosinophils. (Figure 8) However, histopathology is required for definitive diagnosis.
Cytology of pustule contents and / or crusts provides tentative diagnosis. Impression smears of the underside of peeled off crusts and exposed eroded epidermis offer the best chance of recovering acantholytic keratinocytes.
Histopathology (skin biopsies in 10% buffered formalin) pathognomonic lesions enable confirmation of the diagnosis. Minimum of 3 punch biopsies in 10% buffered formalin is required.
Punch skin biopsies (at least 3 but preferably 5-6) collected into 10% buffered formalin for histopathology, are the diagnostic samples of choice for confirmation of the diagnosis. Remember in cats pustules are thin roofed and therefore very delicate, rupturing early and making sampling of intact pustules extremely difficult. Felines produce waves of acantholytic keratinocytes which are then encountered at the same level within multiple biopsies. This shedding of acantholytic keratinocytes into the surface crust highlights the importance of submitting crust material together with the skin biopsies in formalin, as there is a high probability of observing diagnostic acantolytic keratinocytes in crust material. The area should not be prepared prior to biopsy as cleaning reduces the diagnostic value by scrubbing away crusts and superficial epidermis. Obtaining in-tact pustules in biopsies usually requires hospitalization of the patient for vesicle watching ensuring pustules are biopsied as soon as they develop before rupturing.
Histological examination of skin biopsies from cats with PF reveal that acantholytic keratinocytes are numerous in pustules and crusts with rafts being common. Pustules most commonly contain well preserved neutrophils but eosinophils may sometimes be encountered. Follicular involvement is seen in ±25% of cases, while mast cells form a significant component of the dermal infiltrate.
Fig 1: Nasal planum with surface yellow crusts.
Fig 2: Ear pinna inner convex surface revealing multiple crusts, areas of epidermal erosion (arrowhead) and rare intact pustules (arrow)
Fig 3: Ear pinna outer concave surface with multiple crusts with coalescence of many small crusts to form extensive areas of crusting.
Fig 4: Ventral abdomen with multiple surface crusts and epidermal erosions involving the abdominal skin and nipples.
Fig 5: Foot dorsal aspects of alopecia and crusting around the nail beds.
Fig 6: Foot with severe crusting of the nail beds plus the crusting around the outer aspects of the footpads.
*Figures 1-7 courtesy of Dr Marlies Bohm – King Edward Referrals, Port Elizabeth
Figure 8: Cytological smear revealing acantholytic keratinocytes among well preserved neutrophils
In cats, unlike dogs, corticosteroid therapy alone is frequently successful with multidrug protocols being less commonly applied in felines. Recent studies have shown that daily prednisalone at 2 mg/kg as a monotherapy, has proven effective for inducing remission of PF in cats. Adverse effects were uncommon at this low dose and in a small population of these cats, permanent remission may be induced. Some dermatologists prefer a more aggressive initial treatment (4-5 mg/kg prednisolone daily) that induces remission followed by maintenance therapy (2 mg/kg every second day) for long term control. Other glucocorticoids which have proven successful include triamcinolone (0.4 – 0.8 mg/kg/day), methylprednisalone (3 – 5 mg/kg/day) or dexamethasone (0.4 – 0.6 mg/kg/day).
Irrespective of which steroid is used patients should be checked every 2 weeks until no new lesions are seen. As long as new lesions are appearing remission has not been achieved. Once remission has been achieved adjustments in the dose of steroid (reducing mg/kg) and frequency of application (extend to every second or third day) can be considered. Repositol glucocorticoids such as Depo-medrol, have no place in the management of immune mediated diseases.
If steroid monotherapy is unsuccessful then addition second agent to the corticosteroids can be added. Multidrug protocols which have been applied in cats include glucocorticoids plus cyclosporine (5 mg/kg daily) or chlorambucil (0.1 mg/kg daily or 0.25 mg/kg every second day). These multidrug protocols are glucocorticoid sparing.
Safety studies for ciclosporin have shown that doseages used clinically do not have any significant effect on feline blood glucose levels and in general this drug is well tolerated by cats. The most commonly reported adverse effects are vomiting, diarrhoea and anorexia. There are single rare reports of fulminant systemic infections with Toxoplasma and Mycobacteria in cats on ciclosporin. Modified ciclosporin can provide enhanced glucocorticoid sparing for long term disease control. In some cases cats can be weaned off steroids altogether with ciclosporin then used as a monotherapy for maintenance.
The principle adverse reactions documented in cats on chlorambucil include nausea, inappetance and idiosyncratic myelosuppression. Full blood count, blood chemistry, urinalysis, boody weight and appetite should be monitored every 2 weeks during induction therapy and every 6-12 weeks during maintenance.
In general, secondary bacterial infections in cases of PF are of less concern in cats than dogs. If bacterial infection is evident on cytological or histological examination, then topical and systemic antibiotic therapy would be indicated in the initial phases of the immunosuppressive therapy. In cases complicated by previous antibiotic treatment, bacterial culture and antibogram for selection of an appropriate antibiotic is indicated.
In the majority of cases the prognosis for feline PF is fair to good, although most cats require lifelong therapy. The more favourable prognosis in cats compared to dogs is probably related to less frequent drug reactions with many cats responding to corticosteroid monotherapy at low doses with minimal side effects.
Therapy Options at a Glance
Option 1: Prednisalone @ 2 mg/kg/day (remission and maintenance).
Option 2: Prednisalone initial loading @ 4-5 mg/kg/day to induce remission followed by 2 mg/kg/day for maintenance
Option 1: Glucocorticoids plus cyclosporine @ 5 mg/kg/day.
Option 2: Glucocorticoids plus chlorambucil @ 0.25 mg/kg every second day.
Depo Medrol has no place in the management of PF cats
1. Angus J C 2005 Dermatology Secrets: Pemphigus foliaceus in cats. In: Proceedings of the North American Veterinary Conference. Orlando, Florida.
2. Irwin et al. 2012 Use of modified ciclosporin in the management of pemphigus foliaceous: a retrospective analysis. Veterinary Dermatology 23:403-409.
3. Simpson & Burton. 2013 Use of prednisolone as monotherapy in the treatment of feline pemphigus foliaceus: a retrosprective study of 37 cats. Veterinary Dermatology 2013; 24:598-601.
4. Werner A. 2012 Pemphigus foliaceus in cats. Clinical View Dermatology