Scabies and Mange
Erythematous, papular dermatitis of the distal pinnae associated with significant pruritus is an early manifestation of Sarcoptes scabiei in dogs. Crust and scale will usually first affect the tip of the pinna or ear margin. The pinnal-pedal reflex (i.e. rubbing the pinna resulting in a pelvic limb scratch reflex) is often associated with sarcoptic mange but is not pathognomonic for the condition. Concurrent lesions often involve the lateral hocks and elbows and may spread to the rest of the body. The diagnosis is usually made with skin scrapings; however, multiple scrapings may be necessary to achieve the diagnosis. The presence of a single mite, egg, or fecal droppings is diagnostic for the disease. All animals in the household should be treated, and the condition is zoonotic, so owners and handlers should be made aware of the condition. Initial treatment consists of removal of crusts and debris, followed by an acaracidal dip such as lime sulfur, permethrin, organophosphate, or amitraz, which may shorten time to resolution of clinical signs and diminish zoonotic potential. Ivermectin administered subcutaneously, twice at 14-day intervals, or orally three times at 7-day intervals, results in cure. A similar dose schedule exists for milbemcyin. Topical application of selamectin or fipronil may also be curative.
Feline mange, caused by Notoedres cati, results in alopecia, pruritus, excoriations, and thick crusts of the rostral pinnae and is usually restricted to the ears and head. The extremities and perineum may also be affected due to the sleeping and grooming habits of cats. The parasite may also inhabit dogs, foxes, and rabbits; transient lesions have been reported in humans. The diagnosis is made with skin scrapings, and lime sulfur or amitraz dips are effective treatments. Ivermectin given two or three times subcutaneously is also effective.
Fly Strike Dermatitis
Insect bite dermatitis, primarily caused by the stable fly, Stomoxys cakitrans, results in serosanguineous, crusting dermatitis on the ear tips in dogs with erect ears or on the folded edge of the pinna in dogs with pendulous ears. Chronic fly strike dermatitis can become granulomatous in nature. Horse flies (Tabanus species) and deer flies (Chrysops species) may also plague dogs that are housed outdoors, but their bites are usually less reactive than stable flies. The diagnosis is based on an environmental history and response to limiting outdoor exposure. Fly repellents containing permethrin, citronella, or diethyltoluamide (DEET) in petroleum jelly may be used to diminish repeated fly bites. Topical corticosteroid with an antibiotic may hasten the resolution of clinical signs. Black flies (Simulium species) may also cause papular dermatitis and alopecia in dogs.
Cats can develop a seasonal hypersensitivity to mosquito bites. Papules, erythema, alopecia, and hypopigmentation occur on the pinnae and face. Pyrexia, lymphadenopathy, and footpad lesions may also occur.
Actinic Dermatitis and Squamous Cell Carcinoma
Damage to the skin by long-term sun exposure occurs most often in white cats, although the condition is also reported in dogs and in cats with pigmented skin. The pinna is most often affected due to its sparse hair covering; the nose, lips, and eyelids may be similarly affected. Waxing and waning ear tip erythema may progress to the development of fine scale and alopecia early in the disease. Erosive, crusted, hemorrhagic lesions and folding of the pinna occur as a precancerous condition, which may ultimately lead to carcinomatous change., Squamous cell carcinoma is most often diagnosed in older cats (mean age, 12.8 years) with either skin scrapings or biopsy.
Treatment of actinic dermatitis ideally consists of limiting sun exposure between the hours of 10 AM and 4 pm by housing indoors and eliminating sunbathing behavior. Application of sunscreen of SPF 15 or greater may also decrease the effects of solar radiation. β-carotene and canthaxanthin administered orally and the use of retinoic acids (i.e. isotretinoin, etretinate) have also been reported. An initial response to therapy may be seen, but long-term effectiveness has not been thoroughly investigated. Strontium plesiotherapy has been used in the treatment of actinic dermatitis. Failure to respond to medical management is an indication for pinnectomy.
Squamous cell carcinoma is usually locally invasive and slow to metastasize to either local lymph nodes or the lung. Pinnectomy is an effective mode of therapy for severe actinic dermatitis and squamous cell carcinoma. Cryosurgery, radiotherapy, brachytherapy, hyperthermic, and photodynamic therapy have also been used on focal lesions; systemic chemotherapy is not considered effective.
Animals affected by frostbite are usually systemically ill or have recendy moved to a cold environment. The ear tips are pale, cyanotic, hypoesthetic, and cool to the touch after exposure. With warming, the tissues become hyperemic and develop scale, crust, and alopecia. The ear tips may curl, necrose, and eventually slough. Initial treatment consists of rewarming with warm water and subsequent symptomatic therapy for scaling and crusting dermatitis. Amputation of necrotic tissue results in improved cosmesis with haired skin and decreases the risk of recurrent freezing, which is more likely in previously frostbitten tissue.
The underlying cause of vasculitis is often unknown, but the condition occurs subsequent to Type I and Type III hypersensitivity reactions and the deposition of antigen and antibody complex within the vascular wall. The lesions are characterized by erythema, edema, and eventual necrosis and sloughing, leading to a “punched out” or ulcerated appearance to the pinnae. Other affected areas include the lips, tail, pads, and nails. A neutrophilic, eosinophilic, or lymphocytic vasculitis may be evident on histopathology. Proliferative thrombovascular necrosis of the pinnae is a form of vasculitis reported in dogs. Inflammatory vasculitis is not evident in this syndrome and cause is unknown. Conditions such as rickettsial disease, drug eruption, immune-mediated disease, and other underlying systemic conditions should be ruled out. Therapy should be directed at treating the underlying cause. Idiopathic vasculitis cases may respond to immunosuppressive doses of corticosteroids. Other reported treatments include pentoxy-phylline, sulfasalazine, or dapsone. Surgical excision of the affected portion of the pinna with wide surgical margins may be indicated if medical management is unsuccessful.
Crusting and scaling of the pinnae may be caused by idiopathic defects in keratinization, primary disease conditions causing seborrhea, and secondary changes in keratinization due to parasitism. Ear margin dermatosis is common in dachshunds and other breeds with pendulous ears. Seborrheic changes begin at the ear margin and progress to confluence of scale and significant alopecia. Pruritus is variable but may be present in severe cases. The condition is not curable but controllable with keratolytic keratoplastic shampoos (e.g. sulfur-asalicylic acid, benzoyl peroxide or benzoyl peroxide-sulfur, selenium sulfide). Severe cases may require topical or systemic corticosteroid treatment due to inflammation associated with removal of crusts or ear fissure formation.
Sebaceous adenitis is associated with an inflammatory process of the sebaceous glands. Follicular disruption, alopecia, and surface scale initially affect the pinna and may involve the ear canal and trunk. No direct therapy exists for lost sebaceous glands, and supportive care with fatty acids, humectants, and anti-inflammatory corticosteroids can be useful. Retinoids have been used in cases with a granulomatous response to the process.
Other less common disorders can cause hyperkeratosis of the pinna. Idiopathic benign lichenoid keratosis has been diagnosed in four dogs with multiple wartlike papules and hyperkeratotic plaques on the pinnae. Lichenoid psoriaform dermatosis is a rare condition in which erythematous papules and lichenoid plaques appear on the concave surface of the pinna, external ear canal, and ventral head and trunk. Treatment consists of antimicrobial shampoo, systemic antibiotics, and corticosteroids. Lupoid dermatosis is a heritable condition of German short-haired pointers in which progressive, nonpruritic scale occurs on the pinnae, face, and trunk. No therapy is available for the condition.
Zinc deficiency caused by dietary insufficiency or inability to absorb dietary zinc results in crusting lesions of the pinna, and perioral, periorbital, perianal, and perivulvar sites of dogs. Food allergy can result in steroid-resistant alopecia, crust, scale, hyperpigmentation, and lichenification of the pinnae. Dietary restriction followed by feeding trials is diagnostic of the condition, which may be associated with lesions and pruritus on other parts of the body.