The pinnae may be affected by the majority of dermatologic diseases described in dogs and cats. For some diseases the pinna is a preferred or commonly affected site. For a small number of diseases the pinnae are often the only affected site and some of these will be discussed in this session.

Relapsing polychondritis is a rare disease of dogs, cats and humans characterized by inflammation and destruction involving both articular and non articular cartilaginous structures. (Scott, Miller et al. 2001) It has been classified among the immune-mediated diseases because of similarities to rheumatoid arthritis and lupus erythematosus as well as its favorable response to immunomodulatory therapy. In humans, antibodies against type II collagen may be demonstrated in some cases. In dogs and cats it has not been reported to be relapsing and virtually all cases have been limited or apparently limited to involvement of auricular cartilage. (Boord and Griffin 1998) It would appear that aural chondritis is a more appropriate term for this disease syndrome. In one dog and three cats I have no definitive cause was determined though chronic otitis preceded the development of the auricular chondritis. FIV and FeLV are reported in cats though my cases have routinely been negative for these viruses.

Affected cats and dogs presented with a history of swollen, erythematous, painful ears. Examination will show deformed, sometimes curled, swollen usually firm pinnae that are erythematous to violaceous. Cats may be otherwise healthy or may show signs of pyrexia, lethargy, and anorexia. One dog had a history of non erosive polyarthritis and laxity of digital and carpal joints as well as otitis prior to the development of auricular chondritis. One case was seen in a puppy with multiple papules on both pinna that were non painful and of normal skin color.

Biopsies usually reveal lymphoplasmacytic inflammation, loss of cartilage basophilia, and cartilage necrosis. One cat has an eosinophilic mixed infiltrate, and the pathologist suggested and insect bite as an underlying cause.

Cats that are in no pain and show no systemic signs may do fine without therapy. In one cat, systemic glucocorticoids were ineffective, but dapsone (1 mg/kg q24h) induced a remission within 2 weeks. (Scott, Miller et al. 2001) Permanent deformity of the pinnae is to be expected, whether or not the cat is treated. In one dog surgical excision was effective in eliminating the discomfort and gross lesions.

Canine ear margin dermatosis is a scaly, greasy condition of the margin of the pinnae. It is described mainly in dachshunds but other breeds may be affected, most of which have pendulous ears. I have seen this in erect eared dogs and dogs with ear crops as well. Follicular casts and partial alopecia are common. In severe cases secondary infections may occur. Severe cases may develop necrosis or fissures. The concern for a vascular component is then warranted. Usually these cases are asymptomatic unless infected, fissured or necrotic. Moisturizing agents and topical sulfur salicylic acid shampoos and topical hydrocortisone creams are most helpful in managing uncomplicated cases. Severe cases with a vascular necrosis respond best to partial pinnectomy though pentoxifylline may be beneficial and should be tried prior to surgery.

Cutaneous vascular perfusion disorders are uncommon disorder in dogs and cats but when occur often affect the auricle and in many cases may be limited to the apex of the pinnae. One disease, proliferative thrombovascular necrosis, has only been seen involving the pinna. (Scott, Miller et al. 2001) These diseases are characterized by abnormalities in blood flow do to vascular damage which may occur secondary to vessel inflammation (vasculitis), trauma, thrombosis or degenerative changes.

Cutaneous vasculitis often is idiopathic or secondary to vaccines, drug reactions and infections. (Scott, Miller et al. 2001) However causes are quite variable and it may be associated food allergy, insect bites, malignancies, connective tissue disorders such as lupus erythematosus and other immune mediated diseases. Breed predispositions have been described with some forms of idiopathic or vaccine related vasculitis.

Pinnal lesions of vascular perfusion diseases are often distinct and characteristic but not associated with specific causes. Pinna lesions are often more prevalent on the apex and concave surface. Early lesions are scale, alopecia, acrocyanosis or hyperpigmentation. Eventually erosions, crust. There is often a surrounding area of discoloration and vessels may appear more prominent as they approach the lesions. Most often lesions are elongated wedge shaped with the wide base and more severe changes seen towards the ear margin at towards the apex. After necrosis occurs there is permanent deformed pinna. Permanent scarring may occur in the central and more severely affected areas adjacent to areas of necrosis.

Histopathology varies depending on the cause and stage the lesions are sampled. In the cases where active vasculitis is occurring then varying degrees of neutrophilic, eosinophilic or lymphocytic vasculitis, may be present, but usually without fibrinoid necrosis. In some biopsies the diagnosis of vasculitis vasculopathy is suspected on the basis of a cell-poor hydropic interface dermatitis and the loss of definition and staining intensity of hair follicles ("fading follicles"). Proliferative thrombovascular necrosis of the pinnae is characterized by arteriolar proliferation, sclerosis, hyaline degeneration, and eventually thrombosis.⁷ No inflammatory vasculitis is present.

When vaccine induced or related to ischemic dermatopathy then the offending drug or vaccine often was given 2-4 months prior to the initial lesions being noted by the owners. Once the diagnosis of cutaneous vasculitis has been established, it is imperative that underlying etiologic factors be sought and eliminated. If present in your areas then the presence of antibodies for the tick borne and blood borne infectious diseases should be determined.

Treatment of vasculitis consists of correction of the underling cause and immunomodulatory drug treatment. In suspect cases a trial with doxycycline is often prescribed while awaiting biopsy results and prior to initiating immune suppressive therapies as it is effective for many of the blood borne infectious causes of vasculitis. In less severe cases and for all cases of proliferative thrombovascular necrosis initial therapy with pentoxifylline is indicated due to its relative lack of side effects and moderate efficacy. In more severe cases, systemic prednisone or prednisolone (2 to 4 mg/kg orally q24h) is initially utilized with pentoxifylline. For other cases that are refractory to glucocorticoids then cyclosporine and azathioprine may be added to the treatment regimen. Other rarely used treatment options include sulfones, dapsone (1 mg/kg orally q8h, not cats) or sulfasalazine (20 to 40 mg/kg orally q8h. For proliferative thrombovascular necrosis that is unresponsive to pentoxifylline the treatment of choice is partial surgical removal of the pinna. Relapses have occurred only when attempts were made to save as much tissue as possible. Focal cutaneous vasculitis and alopecia subsequent to injections may also respond to pentoxifylline or may be treated by complete surgical excision.

Aural hematomas develop as a result of hemorrhage intrachondrally or parachondrally and are usually brought on by self-trauma. Though it was suggested this may be immune mediated another study refuted this observation and correlated most cases with dermatologic diseases. (Joyce and Day 1997) Some hematomas can be small and present as a soft fluctuate nodular swelling most commonly on the concave surface of the pinna. They may also spread to involve the majority of the scaphae of the auricular cartilage.

Diagnosis is based on the classic clinical lesions. It is important to examine the ear canal and look for causes of aural or head pruritus. It there is a positive pinnal pedal reflex trial selamectin is indicated to rule out sarcoptic mange. Treatment is required to minimize discomfort and secondary scarring and deformity as untreated lesions heals with scars, nodules and folds of the auricular cartilage. Most treatments incorporate drainage of the hematoma, possible flushing of the hematoma space and suturing of the pinna to close the space and prevent repetitive filling with more blood. A non suture less technique just used a Penrose drain with systemic prednisone while another technique was described using carbon dioxide laser. (Joyce 1994; Dye, Teague et al. 2002)

References

1.  Boord, M. J. and C. E. Griffin (1998). "Aural chondritis or polychondritis dessicans in a dog." Proc Acad Vet Dermatol Am Coll Vet Dermatol 14: 65.

2.  Dye, T. L., H. D. Teague, et al. (2002). "Evaluation of a technique using the carbon dioxide laser for the treatment of aural hematomas." J Am Anim Hosp Assoc 38(4): 385-90.

3.  Joyce, J. (1994). "Treatment of canine aural haematoma using an indwelling drain and corticosteroids." J Small Anim Pract 35(7): 341-344.

4.  Joyce, J. and M. Day (1997). "Immunopathogenesis of canine aural haematoma." J Small Anim Pract 38(4): 152-158.

5.  Scott, D. W., W. H. Miller, Jr,, et al. (2001). Muller and Kirk's Small Animal Dermatology. Philadelphia, W.B. Saunders.