Pemphigus foliaceus in a cat

17 Pemphigus foliaceus in a cat




INITIAL PRESENTATION


Crusting skin disease.



INTRODUCTION


Pemphigus foliaceus is an uncommon, sterile pustular, autoimmune skin disease that is recognized in both dogs and cats. The pustules quickly rupture, resulting in the formation of extensive crusting of affected areas. The degree of crusting is one of the diagnostic features of this disease. The definitive diagnosis is confirmed by cytology and histopathological examination.




CASE PRESENTING SIGNS


An 11-year-old female, spayed, black and white domestic short hair was presented with a 2-month history of severe crusting skin lesions.



CASE HISTORY


Typically, pemphigus foliaceus presents with a history of crusting skin lesions that most commonly start over the pinnae and face, with later involvement of the trunk and limbs. Paronychia is a common finding in cats. Pruritus may be absent to severe, and many cases show intermittent depression, pyrexia and anorexia. Quite frequently, when questioned, owners may have recognized a waxing and waning of the symptoms over time.


The relevant history in this case was:


• A 3-month history of crusting lesions initially involving the right pinna with later involvement of the left pinna, face, nasal planum and dorsal trunk. She had also developed a purulent and crusting paronychia. There had been no obvious evidence of pruritus or pain.

• The cat also had a 5-year history of glucocorticoid-responsive, summer seasonal ventral pruritus and symmetrical alopecia over the limbs and tail. Pruritus had persisted despite thorough flea control, but the symptoms had been responsive to corticosteroids. However, corticosteroid therapy had precipitated the onset of diabetes mellitus the previous year and treatment had been withdrawn. The symptoms of diabetes mellitus had resolved on treatment withdrawal.

• She had been anorectic and very lethargic for the past 48 hours.

• There was one other cat in the household, a male sibling, that was unaffected.

• There was no evidence of zoonosis.

• The patient had access to the garden area.

• The cat was fed a diet of various proprietary tinned cat foods.

• She had received routine immunization for feline calici virus, rhinotracheitis and leukaemia 8 months previously. She received regular worming treatment, although not for 2 months prior to the onset of the skin lesions. She received monthly applications of fipronil spot-on.

• At the time of examination, the cat had been treated with enrofloxacin at a dosage of 6 mg/kg s.i.d. with no clinical improvement.

• There had been no response to twice daily applications of a triamcinolone-containing cream to the pinnae.

• Previous histopathological examination had shown a non-specific, superficial inflammatory skin disease.


CLINICAL EXAMINATION



• Rectal temperature was 104.2°F.

• There was moderate peripheral lymphadenopathy.

• There was extensive crusting over the pinnae (Fig. 17.1), bridge of the nose (Fig. 17.2), the pre-auricular skin and one focal crusted lesion over the mid dorsum. Removal of the crust revealed shallow, exudative, erosions.

• There was a purulent paronychia affecting some of the digits on all four feet (Fig. 17.3).

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Figure 17.1 Severe crusting on the pinnae.


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Figure 17.2 Crusting over the bridge of the nose and pinnae.


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Figure 17.3 Purulent and crusting paronychia.




DIFFERENTIAL DIAGNOSES


Crusting is caused by leakage of pus, serum or blood onto the skin surface. In this case the colour of the crust was not consistent with haemorrhage but suggested a purulent discharge. One possible origin of such crusts is from a pustular skin disease.


The combined presence of focal crusting lesions affecting the pinnae and bridge of the nose, along with a purulent paronychia, was highly suggestive of pemphigus foliaceus.


Alternative, but less likely, crusting and erosive skin diseases included:


• Pyoderma

• Dermatophytosis

• Cutaneous or systemic lupus erythematosus

• Vasculopathy or vasculitis

• Cutaneous drug reaction

• Squamous cell carcinoma.


CASE WORK-UP


Cytology is an essential diagnostic tool where there is an exudative discharge. Fungal culture was also indicated to rule out any involvement of dermatophytosis.


The following diagnostic tests were performed:


• Cytology of pus from beneath crusted lesions and from the nail folds, which showed numerous neutrophils and acantholytic keratinocytes (Fig. 17.4).

• Cytology of pus from the nail folds also revealed small numbers of cocci and rods.

• Fungal culture of material taken using a toothbrush technique, which did not grow dermatophytes.

• Histopathological examination of four samples from representative skin lesions, harvested using a 6-mm biopsy punch. There was a mixed superficial perivascular dermatitis, mild to moderate irregular epidermal hyperplasia, and subcorneal pustules/crusts containing mainly non-degenerate polymorphonuclear cells and numerous acantholytic keratinocytes. There was no evidence of bacteria, mites and dermatophytes in the sections examined.

• A blood sample was taken. Routine haematological and biochemical examinations were unremarkable, and FeLV and FIV serology were negative.

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Figure 17.4 Neutrophils and acantholytic keratinocytes (arrowed) on cytology preparation from a cat with pemphigus foliaceus. ×1000 original magnification. Diff Quik® stain.



DIAGNOSIS


The history, clinical signs, cytological and histopathological examinations, and the negative fungal culture, were consistent with a diagnosis of pemphigus foliaceus.



PROGNOSIS


The prognosis for feline and canine pemphigus foliaceus is very variable. Mildly affected cases with localized lesions may respond to topical medications. At the other end of the spectrum, there are very severe cases that may be refractory to therapy or that may develop life-threatening side-effects to treatment. In young animals, permanent resolution may follow successful medical therapy; in other cases, ongoing therapy is required to prevent recrudescence.



AETIOLOGICAL AND PATHOPHYSIOLOGICAL ASPECTS OF PEMPHIGUS FOLIACEUS


Pemphigus foliaceus is currently considered a heterogeneous autoimmune skin disease, resulting from the formation of predominantly IgG1 and IgG4 autoantibodies that target the intercellular spaces of the stratum spinosum and stratum granulosum of the epidermis. The precise target(s) (autoantigens) of these antibodies remain(s) unclear. There have been no studies reporting the nature of the specific autoantigen in cats, but a considerable amount of work has been done in looking for the autoantigen in canine pemphigus foliaceus. It was originally thought that the major autoantigen was desmoglein-1, a component of the desmosomes, which are responsible for keratinocyte–keratinocyte adhesion in the epidermis of the skin and hair follicles, but recent work has shown that this is an antigen of minor importance in canine pemphigus foliaceus, highlighting the heterogeneous nature of this disease.


Pustule formation: The exact mechanism of pustule formation in association with antibody formation is complex and incompletely elucidated. However, antibody binding to desmosomal structures leads to the release of plasminogen by keratinocytes that results in activation of plasmin, a protease that destroys desmosomal structures, leading to acantholysis and the separation of keratinocytes in the stratum spinosum. The clefts thus formed are filled by neutrophils migrating into the epidermis from the circulation to form pustules. Acantholytic keratinocytes, cells that have become detached from the stratum spinosum as a result of the acantholytic process, are also present within the pustules. These cells are nucleated, as opposed to the fully differentiated cells of the stratum corneum that have lost their nuclei. They tend to have a rounded appearance and have basophilic staining characteristics. The cytological finding of acantholytic keratinocytes combined with a neutrophilic infiltrate is consistent with pemphigus foliaceus, but may also be found in cases of bacterial pyoderma and also dermatophytosis, particularly in cases of infection with Trichophyton spp.



Trigger factors


Drug induced: Most cases of pemphigus foliaceus in both cats and dogs appear spontaneously. However, a subset of cases may be drug induced and, in these cases, the disease should resolve when the drug is discontinued. Drug-related pemphigus foliaceus has been reported following administration of cefalexin and trimethoprim-potentiated sulphonamides in dogs, and ampicillin and methimazole in cats.


Chronic skin disease: Anecdotally, dermatologists report cases of canine pemphigus foliaceus that occur in association with a history of chronic skin disease. Typically, these cases have a history of chronic inflammatory, pruritic skin disease and then suddenly develop a more severe disease associated with pustules and crusting, diagnosed as pemphigus foliaceus. Whether there is a cause and effect association with the chronic skin disease is not clear. There is the possibility that some of these cases may be a cutaneous drug reaction associated with drugs used to treat the chronic skin disease.


Sunlight: There is some evidence that sunlight exposure may be a triggering factor for pemphigus foliaceus, particularly in lesions affecting the face. Some experimental work has found that UVB exposure of non-lesional skin from a dog with facial pemphigus foliaceus led to acantholysis.

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Pemphigus foliaceus in a cat

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