Diseases of the Pinna

Chapter 58 Diseases of the Pinna



Lynette K. Cole


The pinna is a mobile structure designed to localize and collect sound waves and transmit them to the tympanic membrane. The pinna has vastly different breed conformations in the dog, while in the cat; there is very little breed variation. The auricular cartilage expands to form the pinna, with the skin of the concave portion of the pinna tightly adherent to this cartilage. The cartilage of the pinna becomes funnel shaped at the opening of the external ear canal.


The pinna is a region of the body prone to numerous skin diseases. In most cases, the pinnal lesions are associated with lesions on other body areas. There are a few diseases where lesions are limited to the pinna (Table 58-1).


Table 58-1 DERMATOSES OF THE PINNA




































































































Affected Site(s) Disease Clinical Lesions Found on Pinna
Pinna only
  Canine eosinophilic pinnal folliculitis Erythema, papules, crusts
Ear margin seborrhea Scale, fissures
Fly bite dermatitis Ulcers, crusts, erythema, alopecia
Proliferative thrombovascular necrosis of the ear pinnae Ulcers, scale, hyperpigmentation
Pinna and other body areas
  Actinic keratoses Erythema, hyperkeratosis, crusts, hyperpigmented plaques
Arteriovenous fistula Edema
Atopic dermatitis Erythema
Canine demodicosis Erythema, papules, scale, alopecia, crusts
Canine sarcoptic mange Erythema, papules, crusts, scale, alopecia, excoriations
Contact dermatitis Erythema, macules, papules, erosions, ulcers
Cutaneous adverse food reaction Erythema
Dermatomyositis Alopecia, erythema, scale, crusts, ulcers, scars
Dermatophytosis Erythema, alopecia, papules, pustules, crusts
Discoid lupus erythematosus Alopecia, crusts, ulcers
Feline demodicosis Erythema, papules, scale, alopecia, crusts
Feline sarcoptic mange Erythema, papules, crusts, scale, alopecia, excoriations
Frostbite Ulcers, necrosis
Hereditary lupoid dermatosis of German short-haired pointers Scale, crusts
Juvenile cellulitis Papules, pustules, crusts
Malassezia pachydermatis Erythema, alopecia, scale, crusts, hyperpigmentation lichenification
Melanoderma and alopecia in Yorkshire terriers Alopecia, hyperpigmentation
Pattern baldness Alopecia, hyperpigmentation
Pemphigus erythematosus Erythema, scale, papules, pustules, alopecia, crusts
Pemphigus foliaceus Erythema, scale, papules, pustules, alopecia, crusts
Psoriasiform-lichenoid dermatosis of springer spaniels Erythema, hyperpigmentation, plaques, papules
Sebaceous adenitis Papules, alopecia, scale, follicular casts
Systemic lupus erythematosus Alopecia, crusts, ulcers
Vasculitis Erythema, alopecia, ulcers, crusts, necrosis
Zinc-responsive dermatosis Erythema, scale, crust, hyperkeratotic plaques

The work-up for all animals with pinnal disease should include a complete history, general physical examination, and dermatologic examination. Next, an otoscopic examination is performed, as well as microscopic examinations of skin scrapings for mites and fungi, cytology for bacteria and yeast, and mineral oil swabs for mites (Otodectes cynotis and Demodex spp.). A bacterial culture is indicated if rod bacteria are seen cytologically. Further testing may be needed such as a complete blood count, serum biochemical profile, urinalysis, allergy testing, food elimination trial, and skin biopsy for histopathology of the ear pinna (see Chapter 59 for diagnosis and treatment of otitis externa).




Key Point


In some cases, the definitive diagnosis of the pinnal disease is made based on the histopathological results from the pinnal biopsy.


The biopsy technique of the ear pinna can be difficult. For lesions on the margin of the pinna, a wedge biopsy is preferred, while for central lesions, a small punch biopsy, size 3.5 to 4 mm, is used to obtain samples. For additional information on the skin biopsy technique, please refer to Chapter 37).



INFECTIOUS DISEASES



Dermatophytosis (also see Chapter 42)



Clinical Signs



• The pinna is often affected in dogs and cats with dermatophytosis.

• In addition to the pinna, lesions may occur anywhere on the body.

• The lesions are quite variable and commonly include erythema, papules, pustules, alopecia, and crusts.


Diagnosis



• Tentative diagnosis: Wood’s lamp examination, microscopic examination of the hair (potassium hydroxide [KOH] preparation, chlorphenolac), and histopathology.

• Definitive diagnosis: positive dermatophyte test medium (DTM) culture.


Treatment



• For localized lesions on the ear pinna only, topical therapy, such as miconazole (Conofite Lotion, Schering-Plough Animal Health) or clotrimazole (Clotrimazole Solution, Vet Solutions), may be effective.

• In generalized conditions where the pinna is not the only affected body site, topical rinses with lime sulfur (LymDyp, DVM Pharmaceuticals) along with systemic therapy (ketoconazole [generics; Nizoral, Janssen] or itraconazole [Sporanox, Janssen]) are necessary for resolution.

• Inform owners that this is a zoonotic disease.


Malassezia Dermatitis (also see Chapter 41)




Clinical Signs



• Malassezia pachydermatis may cause a pruritic dermatitis and otitis in the dog; cats are less frequently affected.

• In addition, the concave and convex portion of the pinna may be affected.

• Lesions include erythema, alopecia, scale, crusts, hyperpigmentation, and lichenification.


Diagnosis



• Obtain samples for cytology by skin scrapes, acetate tape preparations, swabs, and impression smears.

• The yeast organisms are identified microscopically.


Treatment



• Topical therapy (miconazole, ketoconazole, chlorhexidine) in the form of lotions, sprays, leave-on conditioners, shampoos, or medicated pads

• Systemic therapy: oral ketoconazole ([generics; Nizoral, Janssen] or itraconazole [Sporanox, Janssen])

• Identification of the underlying dermatologic condition, such as allergic or endocrine diseases, that triggered the secondary infection.


Parasitic Diseases



Sarcoptic Mange (also see Chapter 44)



Clinical Signs



• Canine scabies (sarcoptic mange) is caused by the mite Sarcoptes scabiei var. canis, while feline scabies (notoedric mange) is caused by Notoedres cati.

• Both diseases cause intense pruritus and are contagious to other animals and humans.

• The lesions frequently start at the edge of the pinna.

• In dogs, the lesions may then spread to the ventral portions of the abdomen, chest, elbows, and legs.

• In cats, the lesions rapidly spread to the face, eyelids, and neck.

• The lesions consist of erythematous papules, thick crusts, scales, alopecia, and excoriations.


Diagnosis



• Perform superficial skin scrapings in animals suspected of sarcoptic mange.

• The mites may be extremely difficult to find; therefore, a negative skin scraping does not eliminate scabies as the cause of the lesions and pruritus.



Key Point


Pinnal pedal scratch reflex (vigorously rubbing the tip of one ear flap on the base of the ear with a response of a scratching movement of the ipsilateral hind leg) for the diagnosis of sarcoptic mange in the dog was found to have a sensitivity and specificity of 81.8% and 93.8%, respectively.



• In the absence of identification of the mites, make the diagnosis of scabies based on response to therapy.


Treatment



• In multiple-pet households, treat all other in-contact animals.

• Conventional therapy consists of weekly lime sulfur dips (LymDyp, DVM Pharmaceuticals) for 6 to 8 weeks.

• Selamectin (Revolution, Pfizer Animal Health) is a novel, semi-synthetic avermectin approved for treatment of canine sarcoptic mange.

• Extra-label treatments (see below) for sarcoptic mange have also been used successfully, including amitraz dips (Mitaban, Pfizer Animal Health), ivermectin (Ivomec 1% injection for cattle and swine, Merial) (this form and dosage of ivermectin should not be given to collies, Shetland sheepdogs, Old English sheepdogs, other herding dogs, or their crosses), and milbemycin oxime (Interceptor Flavor Tabs, Novartis) (low incidence of side effects in collies).


Canine Demodectic Mange (also see Chapter 43)



Clinical signs



• Demodectic mange in the dog is caused by Demodex canis.

• Both the localized and generalized form may affect the ear pinna, in addition to other areas of the body.

• Lesions of demodicosis in dogs consist of erythema, scale, alopecia, papules, pustules, crusts, and secondary bacterial infections.


Diagnosis



• Make the diagnosis by identifying multiple demodectic mange mites on deep skin scrapings.


Treatment



• The majority of localized demodicosis cases will resolve without treatment; however, topical benzoyl peroxide (Pyoben Gel, Virbac; OxyDex Gel, DVM Pharmaceuticals) may be used on the alopecic areas.

• In cases of generalized demodicosis, the FDA-approved treatment is bi-weekly dips with amitraz (Mitaban, Pfizer Animal Health).

• Extra-label daily high dose ivermectin (Ivomec 1% injection for cattle and swine, Merial) or milbemycin oxime (Interceptor Flavor Tabs, Novartis) is effective in the treatment of generalized demodicosis. As stated previously, this form and dosage of ivermectin should not be given to collies, Shetland sheepdogs, Old English sheepdogs, other herding dogs, or their crosses.


Feline Demodectic Mange (also see Chapter 43)



Clinical Signs



• Demodectic mange in the cat is caused by two mites, Demodex cati and Demodex gatoi.

• D. cati is a rare disease.

• The localized form affects the head and neck while the generalized form affects the head, neck, trunk, and limbs

• Lesions consist of erythema, papules, alopecia, scales, and crusts.

• Generalized demodicosis is usually associated with an underlying disease (diabetes mellitus, feline leukemia virus infection, feline immunosuppressive virus infection).

• Mites have been isolated from skin scrapings of the external ear canal.

• Lesions of D. gatoi consist of alopecia, scale, and crusts of the head, neck, and elbows or non-inflammatory alopecia of the ventral abdomen.

• D. gatoi is contagious to other cats.


Diagnosis



• Diagnosis is based on identification of the mites on skin scrapings, deep scrapings for D. cati, and superficial scrapings for D. gatoi.


Treatment



• Treatment consists of weekly lime sulfur dips (LymDyp, DVM Pharmaceuticals).

• For D. gatoi, treat all in-contact cats.

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