Chapter 58 Diseases of the Pinna
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).
|Affected Site(s)||Disease||Clinical Lesions Found on Pinna|
|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|
|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|
|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).
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).
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.