Feline pemphigus foliaceus: original case series and a comprehensive literature review

Feline immune-mediated skin disorders: Part 1

PRACTICAL RELEVANCE

Cutaneous immune-mediated diseases in cats can present with clinical signs of erythema, hair loss, scaling/crusting and erosions with or without pruritis, mimicking many differential diagnoses such as hypersensitivity dermatitis and infections (eg, parasitic and fungal dermatitis). Veterinarians are encouraged to become familiar with the characteristic clinical features of various immune-driven skin disorders to permit early diagnosis and appropriate treatment.

CLINICAL CHALLENGES

Diagnosis and therapeutic management of feline immune-mediated skin diseases can be challenging. Although immune-mediated skin diseases in cats are rare, these can be associated with severe systemic clinical signs, which can lead to poor quality of life and owners electing euthanasia.

AIMS

In the first of a two-part article series, the clinical presentations of feline immune-mediated skin diseases related to the pemphigus complex, cutaneous lupus erythematosus, and thymoma- and non-thymoma-associated exfoliative dermatitis are reviewed and differential diagnoses, diagnosis and therapeutic approach are discussed. In Part 2, the equivalent is discussed for erythema multiforme, f Stevens-Johnson syndrome/toxic epidermal necrolysis spectrum, plasma cell pododermatitis, proliferative and necrotizing otitis externa, pseudopelade, alopecia areata and auricular chondritis.

EVIDENCE BASE

The information in this article is based on a review of the existing veterinary literature.

Canine and Feline Pemphigus Foliaceus-an Update on Pathogenesis and Treatment

Pemphigus foliaceus (PF) is one of the most common autoimmune skin diseases of dogs and cats and is characterized by the development of pustules, crusts, erosions, scales, and alopecia. Albeit poorly understood, the pathophysiology of canine and feline PF appears to involve immune dysregulation and immunoglobulin G autoantibodies that are directed against the keratinocyte cell surface. At present, the management of canine and feline PF relies on the long-term to lifelong prescription of immunosuppressive medications. Current knowledge on the pathogenesis of canine and feline PF, as well as traditional and emerging therapies used to treat both diseases, will be reviewed herein.

Pharmacology of drugs used in autoimmune dermatopathies in cats and dogs: A narrative review

Immunosuppressive drugs are the mainstay of treatment for many feline and canine autoimmune skin diseases, either as monotherapy or in combination with other drugs. Treatment with these drugs is often lifelong and may have long-term consequences on the affected animal's overall quality-of-life. Clinicians need to understand the pharmacology of immunosuppressants in planning and executing the treatment regimen for the best possible clinical outcome, as well as reducing the risk of adverse effects. This review paper will focus on the mechanism of action, pharmacokinetics and pharmacodynamics, clinical uses and adverse effects of immunosuppressive drugs used to treat autoimmune dermatoses in cats and dogs. These include glucocorticoids, ciclosporin A, azathioprine, chlorambucil, mycophenolate mofetil, oclacitinib and Bruton's tyrosine kinase inhibitors.

Generalised pustular onychopathy of unknown aetiology in a domestic cat

Claw diseases are rare in cats and often associated with cutaneous lesions in other regions of the body. This case report describes an atypical manifestation of a generalised onychopathy of unknown origin in a domestic short hair cat.

[Eccrine adenoma in a cat]

Tumors originating from eccrine glands are rare findings in dogs and cats. In most cases, the tumors are malignant, while adenomas are only reported anecdotally. In the present case, a one-year-old female, spayed cat was presented with a swelling of the footpad of the right forelimb. Initially, the mass possessed a diameter of 2 cm which progressed to 4 cm within the following two months. At the latter time point the tumor was ulcerated. After surgical removal, histological and immunohistochemical analyses were performed. Histologically, a well demarcated, nodular, multilobular mass was present. The cuboidal to columnar neoplastic cells were arranged in tubular and acinar structures. Tumor cells possessed large, round to oval nuclei with moderately distinct nucleoli. Mitotic figures averaged 0-1 per high power field. Additionally, large areas of chondroid metaplasia were evident. Immunohistochemically, neoplastic cells were positive for pan-cytokeratin AE1/AE3 whereas thyroid transcription factor 1 (TTF1) was not expressed. Based on the histological and immunohistochemical findings an adenoma of the eccrine glands was diagnosed.

Successful management of feline pemphigus foliaceus with pentoxifylline and topical hydrocortisone aceponate

The treatment regimen for feline pemphigus foliaceus (PF), an autoimmune disease caused by auto-antibodies against proteins of the desmosome junction, usually includes high doses of oral or parenteral immunosuppressive drugs, typically glucocorticoids. This case adds to a growing body of evidence that topical hydrocortisone aceponate is effective for the treatment of feline PF, and demonstrates the practical use of a non-invasive diagnostic method for histopathology when owners refuse a biopsy to support a clinical diagnosis of PF. Finally, this case highlights an international trend of owner-initiated treatment of feline infectious peritonitis (FIP) using unlicensed, unregistered drugs.

Chronic paronychia in cats with patellar fracture and dental anomaly syndrome

CASE SERIES SUMMARY

The aim of this case series was to describe the clinical features and treatment of paronychia in cats diagnosed with patellar fracture and dental anomaly syndrome (PADS). Clinical records, photographs, microbiology, cytology and histopathology reports were collected, and follow-up was obtained. Five cats with paronychia were included. All five cats had multiple digits of multiple limbs affected and eventually underwent amputation of the third phalanx of one or multiple digits. A total of 36 digits were affected, 17% (n = 6/36) resolved with medical management and 83% (n = 30/36) were eventually treated successfully by amputation. The cats had treatment with numerous courses of antibiotics (range 7-20; mean 11 courses) over periods of time ranging from 10 to 67 months (mean 32 months).

RELEVANCE AND NOVEL INFORMATION

Chronic paronychia may be an additional clinical feature of PADS and the probable mechanism involves poor integrity of osteopetrotic bone, loss of normal nailbed anatomy and secondary osteomyelitis of the distal phalanx. Medical management with antibiotics, anti-inflammatory therapy and steroid treatment may improve the clinical signs in the short term; however, in severe instances, amputation of the third phalanx of the affected digit seems to be necessary to resolve repeated recurrences and discomfort. Additional information on the long-term outcome is required. In any cat with atraumatic patellar fractures and/or retained deciduous teeth, paronychia may require surgical management if medical management is unsuccessful.

Comorbidity of ectopic thymoma-associated exfoliative dermatitis and pemphigus foliaceus in a cat

An 8-year-old cat was presented with pruritus, purulent paronychia, scaling, crusting, and spontaneous alopecia. Histopathology revealed intraepidermal neutrophilic pustular acantholytic dermatitis and hyperkeratotic cytotoxic interface dermatitis. No thoracic mass was seen on a lateral radiograph. Ectopic thymoma was discovered on necropsy. This case highlights the necessity for thorough investigation of any case of feline exfoliative dermatitis and pemphigus foliaceus for the presence of thymoma. Key clinical message: Comorbidity of exfoliative dermatitis and pemphigus foliaceus in a cat should prompt a thorough investigation for presence of a thymoma, possibly with advanced imaging techniques.

Chronic Otitis in Cats: Clinical management of primary, predisposing and perpetuating factors

PRACTICAL RELEVANCE

Chronic otitis can be one of the most frustrating diseases to manage for a small animal practitioner. While it occurs less commonly in the cat than the dog, it is no less challenging. The purpose of this review is to discuss the common and uncommon causes of chronic otitis in the cat within the clinical framework used for diagnosis and treatment. The focus is on diseases that affect the ear canal, rather than those restricted to the pinnae.

CLINICAL CHALLENGES

Otitis is multifactorial, which complicates management. A common clinical mistake is to focus solely on treating the infection present. Only by addressing all factors will a clinician successfully control chronic otitis. For the purposes of this review, the authors have adopted the established model of separating primary, predisposing and perpetuating causes of otitis. Primary factors are those that directly cause otitis (inflammation); predisposing factors are those that put the patient at risk for development of otitis; and perpetuating factors are those that result in ongoing clinical signs of otitis or that prevent clinical resolution.

AUDIENCE

This review is aimed at veterinarians who treat cats and particularly those with an interest in feline dermatology and otology.

EQUIPMENT

While many practitioners rely on a hand-held otoscope, a video-otoscope can be very helpful for the diagnosis and treatment of chronic otitis.

EVIDENCE BASE

This review presents up-to-date information regarding the diagnosis and treatment of chronic otitis in cats, with emphasis on the most recent peer-reviewed literature.

Beneficial effect of oclacitinib in a case of feline pemphigus foliaceus

Pemphigus foliaceous (PF) is a pustular, immune-mediated skin disease characterised by acantholytic cells and commonly treated with high doses of glucocorticoids. This report describes one case of feline PF successfully controlled using oral oclacitinib, suggesting a possible therapeutic alternative to glucocorticoids in some cases.

Deep pemphigus (pemphigus vulgaris, pemphigus vegetans and paraneoplastic pemphigus) in dogs, cats and horses: a comprehensive review

Pemphigus is the term used to describe a group of rare mucocutaneous autoimmune bullous diseases characterized by flaccid blisters and erosions of the mucous membranes and/or skin. When the autoantibodies target desmosomes in the deep layers of the epidermis, deep pemphigus variants such as pemphigus vulgaris, pemphigus vegetans and paraneoplastic pemphigus develop. In this article, we will review the signalment, clinical signs, histopathology and treatment outcome of pemphigus vulgaris, pemphigus vegetans and paraneoplastic pemphigus in dogs, cats and horses; where pertinent, we compare the animal diseases to their human homologue. Canine, feline and equine pemphigus vulgaris, pemphigus vegetans and paraneoplastic pemphigus have many features similar to the human counterpart. These chronic and often relapsing autoimmune dermatoses require aggressive immunosuppressive therapy. In animals, the partial-to-complete remission of pemphigus vulgaris and pemphigus vegetans has been achieved with high dose glucocorticoid therapy, with or without adjunct immunosuppressants; the prognosis is grave for paraneoplastic pemphigus.

Detection of circulating anti-keratinocyte autoantibodies in feline pemphigus foliaceus

BACKGROUND

Circulating anti-keratinocyte immunoglobulin (Ig)G targeting desmosomal proteins have been identified in people and dogs with pemphigus foliaceus (PF). By contrast, detection attempts in PF-affected cats have been largely unsuccessful.

HYPOTHESIS/OBJECTIVES

To detect circulating anti-keratinocyte autoantibodies in PF-affected cats and determine their titres and tissue-staining patterns.

ANIMALS

Thirty PF-affected cats were compared to 11 specific-pathogen free, 15 healthy and 31 allergic cats.

METHODS AND MATERIALS

Sera were tested by indirect immunofluorescence on canine footpad and buccal mucosal substrates.

RESULTS

Circulating, anti-keratinocyte IgG with a suprabasilar, web-like (intercellular) pattern were detected in the majority of PF-affected cats (23 of 30, 77%), some allergic cats (six of 31, 19%) and one healthy cat (7%). Both footpad epidermis and buccal mucosa were positive in the majority of seropositive PF-affected cats (21 of 23, 91%), and in only one of six (17%) seropositive allergic cats. Staining was limited to the footpad in the remaining seropositive PF-affected and allergic cats and one seropositive healthy cat. Reciprocal IgG titres were significantly higher in PF-affected cats compared to controls (Dunn's post-test, P < 0.0001). Anti-keratinocyte IgM, IgA or IgE were not detected in any sera.

CONCLUSIONS AND CLINICAL IMPORTANCE

These results confirm the presence of circulating anti-keratinocyte IgG in a majority of PF-affected cats and in a small percentage of healthy and allergic cats. Although the molecular target and pathogenic nature of the antibodies remains unknown, the detection of positive immunostaining on buccal mucosal tissue, in addition to the footpad, suggests that the major target antigen of feline PF differs from that reported in dogs.