History
A 7-month-old sexually intact male domestic longhair cat was evaluated because of unusual skin lesions affecting both ears. The cat had been relinquished by its owner to a county animal shelter. No medical history was available.
Clinical and Gross Findings
On physical examination, the cat was in good body condition with abnormalities limited to both external ear canals and pinnae. The cat had locally extensive crusted and hyperkeratotic proliferative plaques that filled the external and vertical ear canals and extended onto 35% to 50% of the proximal concave portions of both pinnae. Lesions were multifocal at the margins. Surface crusts were brown to black and friable; disturbance of the crusts revealed underlying erythematous proliferative tissue with multifocal erosions. Noncrusted areas had a rough surface with barely visible short papillary-like projections in some locations. A thick purulent exudate was present between some of the lesions, and cytologic examination of a sample of the exudate revealed degenerate neutrophils and small to moderate numbers of gram-positive cocci. Via otoscopic examination, the horizontal ear canals were normal in appearance and the tympanic membranes were intact. The lesions neither appeared painful nor were pruritic. An ELISAa for circulating FeLV antigen and anti-FIV antibodies yielded negative results. Serum biochemical analysis and CBC results were within reference ranges. The cat was anesthetized, and multiple biopsy samples were obtained from both ears (Figure 1).
Photographs of the left (A) and right (B) ears of a 7-month-old male domestic longhair cat that was examined because of nonpainful, proliferative, hyperkeratotic plaques of both external ear canals and proximal portions of the pinnae.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
Photographs of the left (A) and right (B) ears of a 7-month-old male domestic longhair cat that was examined because of nonpainful, proliferative, hyperkeratotic plaques of both external ear canals and proximal portions of the pinnae.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
Photographs of the left (A) and right (B) ears of a 7-month-old male domestic longhair cat that was examined because of nonpainful, proliferative, hyperkeratotic plaques of both external ear canals and proximal portions of the pinnae.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page →
Histopathologic Findings
Histologic examination of the skin biopsy samples revealed markedly hyperplastic epidermis and follicular infundibula with superimposed multifocal single cell necrosis of keratinocytes at different epithelial levels as well as lymphocytic exocytosis (Figures 2 and 3). Mixed orthokeratotic and parakeratotic hyperkeratosis involved the epidermis and the follicular infundibula, where the follicular lumens were greatly dilated and occluded, and was accompanied by neutrophils in multifocal crusts. Epidermal hydropic change caused superficial epidermal pallor multifocally. Mixed, mild, lymphoplasmacytic, neutrophilic, and perivascular eosinophilic infiltrates were present in the dermis.
Low-magnification photomicrograph of a tissue section from an area of skin with lesions on the concave aspect of a pinna of the cat in Figure 1. Raised, proliferative epidermal lesions include marked hyperplasia, hyperkeratosis, and elongation of follicular infundibula (arrows). Hyperkeratosis extends over the surface of the epidermis and mixes with small foci of darker staining crusts. H&E stain; bar = 500 μm.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
Low-magnification photomicrograph of a tissue section from an area of skin with lesions on the concave aspect of a pinna of the cat in Figure 1. Raised, proliferative epidermal lesions include marked hyperplasia, hyperkeratosis, and elongation of follicular infundibula (arrows). Hyperkeratosis extends over the surface of the epidermis and mixes with small foci of darker staining crusts. H&E stain; bar = 500 μm.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
Low-magnification photomicrograph of a tissue section from an area of skin with lesions on the concave aspect of a pinna of the cat in Figure 1. Raised, proliferative epidermal lesions include marked hyperplasia, hyperkeratosis, and elongation of follicular infundibula (arrows). Hyperkeratosis extends over the surface of the epidermis and mixes with small foci of darker staining crusts. H&E stain; bar = 500 μm.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
High-magnification photomicrograph of a tissue section from an area of skin with lesions on the concave aspect of a pinna of the cat in Figure 1. The epidermis (E) is markedly hyperplastic and contains multifocal single cell necrosis of keratinocytes (arrows). Numerous small basophilic lymphocytes are scattered individually in the epidermis and occasionally in the superficial dermis (D). The stratum corneum (SC) is hyperkeratotic and partially parakeratotic. H&E stain; bar = 100 μm.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
High-magnification photomicrograph of a tissue section from an area of skin with lesions on the concave aspect of a pinna of the cat in Figure 1. The epidermis (E) is markedly hyperplastic and contains multifocal single cell necrosis of keratinocytes (arrows). Numerous small basophilic lymphocytes are scattered individually in the epidermis and occasionally in the superficial dermis (D). The stratum corneum (SC) is hyperkeratotic and partially parakeratotic. H&E stain; bar = 100 μm.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
High-magnification photomicrograph of a tissue section from an area of skin with lesions on the concave aspect of a pinna of the cat in Figure 1. The epidermis (E) is markedly hyperplastic and contains multifocal single cell necrosis of keratinocytes (arrows). Numerous small basophilic lymphocytes are scattered individually in the epidermis and occasionally in the superficial dermis (D). The stratum corneum (SC) is hyperkeratotic and partially parakeratotic. H&E stain; bar = 100 μm.
Citation: Journal of the American Veterinary Medical Association 241, 5; 10.2460/javma.241.5.567
Morphologic Diagnosis
Marked, bilateral, hyperplastic, lymphocytic otitis externa with individual keratinocyte necrosis and mild, bilateral, suppurative otitis externa.
Discussion
The proliferative ear lesions and the histopathologic findings were consistent with feline proliferative and necrotizing otitis externa, which is an uncommon disorder. The cause of feline proliferative and necrotizing otitis externa is not known.1–3 Detection of bacteria during cytologic evaluation of ear lesions and a histopathologic diagnosis of suppurative otitis externa support a secondary bacterial infection. In tandem, the recognizable skin lesions and histopathologic changes allow the diagnosis of this unique condition to be made. Bilateral, well-demarcated, coalescing erythematous plaques involving the concave aspect of the pinnae and external ear canals are highly characteristic of this disorder.1,2 Additionally, brown to black surface crusts are mixed with variable amounts of hyperkeratotic surface scale and can be extensive, contributing to occlusion of the ear canals in some cats. Key histopathologic features are marked epidermal hyperplasia, hyperkeratosis, single cell necrosis of keratinocytes, and lymphocytic exocytosis. Lymphocytes usually satellite some of the necrotic keratinocytes. Lesions are typically prominent in the infundibula of hair follicles, which are markedly hyperplastic, elongated, and distended by follicular hyperkeratosis.1 Although some authors have reported involvement of the follicular external root sheath,2,3 other authors have not.1 Follicular external root sheath involvement was not a feature in the cat of the present report. Neutrophilic inflammation can be variable. Histopathologic lesions can resemble hyperkeratotic erythema multiforme of dogs.1 Skin lesions are not troublesome for some cats, as were the lesions in the cat of this report, but appear painful or are pruritic in others.2 Secondary bacterial or yeast otitis is not an uncommon finding in affected cats and contributes to suppurative exudates and crusting. This condition most often develops in young cats (2 to 6 months of age), and lesions develop and progress rapidly.1 Lesions frequently spontaneously regress when the cats reach 1 to 2 years of age. In some cats, the lesions develop later in life, at 2 to 5 years of age, and may remain persistent and refractory to most routine topical treatments.2 Results of immunohistochemical testing of lesions for feline herpesvirus and feline papillomavirus were reported to be negative in 1 study.2 Other proposed causes have included food sensitivity and drug eruptions.1,2
Topically and orally administered antimicrobials and topically administered corticosteroids as well as ear mite medications have been used to treat this disorder without success.2 Feeding novel protein and hydrolyzed protein diets to affected cats has also been reported to be unsuccessful.2
Topical application of 0.1% tacrolimus ointment2 to affected areas every 12 to 24 hours in 3 adult cats has recently been reported to have led to clinical regression of the skin lesions.2 Duration of treatment ranged from 2 weeks (80% resolution) to > 1 year.2 In 1 refractory case, oral administration of prednisolone was also required to achieve resolution.2 Tacrolimus, a calcineurin inhibitor, suppresses T-cell activation and proliferation and antigen presentation and has better penetration of the stratum corneum than does cyclosporine, another member of the same drug class.3–6 Tacrolimus is approved in human medicine for treatment of atopic dermatitis and is used in veterinary medicine to treat conditions such as localized atopic dermatitis and discoid lupus erythematosus.3–7
For the cat of the present report, topical treatment with tacrolimus once daily was commenced. During a 1-month follow-up telephone conversation, the new owner of the cat reported that the cat had no signs of discomfort and skin lesions were improving. Subsequently, the cat was lost to follow-up.
References
1. Ihrke PJ, Walder EJ, Affolter VK. Necrotizing diseases of the epidermis. In: Gross TL, ed. Skin diseases of the dog and cat. 2nd ed. Ames, Iowa: Blackwell Science Ltd, 2005;79–81.
2. Mauldin EA, Ness TA, Goldschmidt MH. Proliferative and necrotizing otitis externa in four cats. Vet Dermatol 2007; 18:370–377.
3. Vidémont E, Pin D. Proliferative and necrotising otitis in a kitten: first demonstration of T-cell–mediated apoptosis. J Small Anim Pract 2010; 51:599–603.
4. Kino T, Hatanaka H, Hashimoto M, et al. FK-506, a novel immunosuppressant isolated from Streptomyces. I. Fermentation isolation, physic-chemical and biological characteristics. J Antibiot (Tokyo) 1987; 40:1249–1255.
5. Kang S, Lucky AW, Pariser D, et al. Long-term safety and efficacy of tacrolimus ointment for the treatment of atopic dermatitis in children. J Am Acad Dermatol 2001; 4:S58–S64.
6. Griffies JD, Mendelsohn DL, Rosenkrantz WS, et al. Topical 0.1% tacrolimus for the treatments of discoid lupus erythematosus and pemphigus erythematosus in dogs. J Am Anim Hosp Assoc 2004; 40:29–41.
7. Marsella R, Nicklin CF, Saglio S, et al. Investigation on the clinical efficacy and safety of 0.1% tacrolimus ointment (Protopic) in canine atopic dermatitis: a randomized double-blinded, placebo-controlled cross over study. Vet Dermatol 2004; 15:294–303.
