Many of the diseases of the ear start with lesions on the external ear pinna. It is important when examining the ear to look for primary lesions which can give a clue to the underlying aetiology of the disease. Primary lesions can be arranged into seven different classes (see box) and although there is some overlap among the classes, this acts as a useful starting point in defining a list of differential diagnoses. Differential diagnoses for each disease includes the other diseases presenting with the same clinical signs within the group.

A range of diagnostic tests can be employed to investigate each disease. The reader is referred to Chapter 2 for details of these.

4.1 ERYTHEMATOUS DISEASES

4.1.1 Allergy

Allergic skin disease typically affects the ear pinna. Atopy, food allergy, and allergic and irritant contact dermatitis can all affect this site. It is unusual for dogs and cats with flea allergic dermatitis to present with pinnal signs although sticktight fleas can attach to this site.

Atopy

Aetiology and Pathogenesis

The most recent theories on the pathogenesis of atopy suggest (to put it simply) that environmental allergens access and are processed by Langerhans cells in the skin, after percutaneous absorption. A T helper 1 (Th1) and T helper 2 (Th2) lymphocyte imbalance in atopic animals leads to amongst other things increased Th2 activity and overproduction of immunoglobulin (IgE). The resulting cascade of events triggers inflammation and pruritus. In addition, atopic animals are also thought to have epidermal barrier defects.

Clinical Signs

Clinical signs generally start between 1–3 years of age. Breed predisposition depends on the local gene pool. Where sensitivity is to pollen the otitis is likely to be seasonal. Animals allergic to house dust mites may have perennial disease but in Europe are often worse in the late autumn and early winter. In addition to otitis animals may have involvement of the skin in the periocular, feet, perianal, groin and axilla areas. In 80% of atopic dogs there are signs of otitis externa, usually with generalized skin disease. However, 20% of atopic dogs only have otitis externa, usually affecting both ears. Typical clinical signs are erythema of the pinna (Figs 4.1, 4.2) and vertical canal. Dogs will present with head shaking (Figs 4.3, 4.4)or rubbing the side of their heads. In some cases this can lead to aural haematoma formation (Fig. 4.5). Chronic changes on the ear pinna in uncontrolled disease include hyperpigmentation and lichenification (Fig. 4.6). Atopic cats may also present with otitis externa. Clinical signs include head shaking and erythema of the ear pinna (Fig. 4.7) or lesions of the eosinophilic granuloma syndrome.

Figure 4.1 Self-inflicted trauma and erythema on the ear pinna of an atopic dog.

Figure 4.2 Erythema of ear pinna in an atopic dog.

Figure 4.3 Mild trauma to ear tip due to head shaking in an atopic dog.

Figure 4.4 Marked trauma to ear tip due to head shaking in an atopic dog.

Figure 4.5 Aural haematoma on ear of dog due to head shaking.

Figure 4.6 Chronic change on the ear of an atopic dog.

Figure 4.7 Erythema of ear pinna of an atopic cat.

Key Diagnostic Tests

• Rule out of other causes of pruritus, especially ectoparasites and infection.
  
• Rule out cutaneous adverse food reaction and allergic/irritant dermatitis.
  
• Specific intradermal or serologic allergy tests are useful in the management but not the diagnosis of the disease.

Food Allergy

Aetiology and Pathogenesis

Food allergy or cutaneous adverse food reaction (CAFR) is caused by an abnormal response to ingested food. Many different mechanisms exist including immunological components, metabolic reactions and food idiosyncrasies. Beef, chicken, dairy products, cereals, soya and egg have been implicated as common causes of CAFR in the dog. Similar substances are thought to be important in the cat. CAFR commonly coexists with atopy.

Clinical Signs

It is reported that 88% of food allergic dogs have signs of otitis externa. Food allergy commonly affects young dogs but it also seen in older animals with no previous history of skin disease. Labradors may be predisposed (Fig. 4.8). In dogs clinical signs commonly mimic those of atopic disease with signs of pinnal erythema and head shaking. Primary lesions are uncommon. Unlike many cases of atopic disease, CAFR is not seasonal. Cats with food allergy typically present with facial pruritus, crusting, and secondary excoriation; the ear may be involved (Fig. 4.9).

Figure 4.8 Erythema of ear pinna of allergic Labrador with a cutaneous adverse food reaction.

Figure 4.9 Facial and aural pruritus in a cat with food allergy.

Key Diagnostic Tests

• Diet trial using novel ingredients to which the dog or cat has had no or minimal exposure, or a hydrolysed diet, should be fed for up to 8 weeks.
  
• Dietary challenge should be performed once resolution has been achieved.

Allergic and Irritant Contact Dermatitis

Aetiology and Pathogenesis

These two conditions are very similar and are caused when an environmental substance has direct contact with the skin. Substances that affect the ear pinna and canal are generally liquids (creams, gels, lotions, etc.). Allergic contact dermatitis is a type IV hypersensitivity whereas irritant contact dermatitis is caused by noxious substances. Any topical medication may cause a reaction. However, neomycin and propylene glycol, which is a common component of many different ear drops and cleaners, have been implicated as causal agents.

Clinical Signs

Both of these conditions are less common than both food allergy and atopy as a cause of otitis externa. Allergic contact dermatitis takes multiple exposures to induce a reaction and affects individual animals. Irritant contact dermatitis causes a reaction on the first exposure and affects all in-contact animals. Typically dogs and cats will fail to respond to rational topical drugs and their disease deteriorates as therapy continues. Clinical signs usually start 1–3 days after the start of therapy. Lesions consist of erythema, oedema, erosions and in severe cases ulceration (Figs 4.10, 4.11).

Figure 4.10 Erythema and ulceration of ear canal in a dog with irritant contact dermatitis due to ear drops.

Figure 4.11 Close-up of Figure 4.10.

Key Diagnostic Tests

• Ruling out of other allergic triggers, removal of topical therapy with subsequent improvement.
  
• Rechallenge should be avoided.

4.1.2 Immune-Mediated Disease

Feline Relapsing Polychondritis (Auricular Chondrosis)

Aetiology and Pathogenesis

Very rare, poorly understood disease thought to be an immune-mediated attack against collagen. Cats are often feline leukaemia virus (FeLV) or feline immunodeficiency virus (FIV) positive. It has also been recorded in dogs.

Clinical Signs

The ear pinna is swollen, erythematous to violaceous and painful (Fig. 4.12). In more chronic cases the pinna may be curled and deformed. Involvement of other organs, e.g. the joints, heart and eyes, have been described. Some cats may show signs of pyrexia and lethargy.

Figure 4.12 Feline relapsing polychondritis.

Key Diagnostic Tests

• Bloods show neutrophilia, lymphocytosis, hyperglobulinaemia.
  
• Biopsy of the pinna reveals a lymphoplasmacytic inflammation with loss of cartilage, basophilia and cartilage necrosis.

4.2 DISEASES WITH CRUST AND SCALE

4.2.1 Infections

The most common infectious diseases to present with crusting and scaling are dermatophytosis, yeast infections and leishmaniasis.

Dermatophytosis

Aetiology and Pathogenesis

In dogs the most common causes for dermatophytosis are Microsporum canis and M. gypseum. Other less frequent species include Trichophyton mentagrophytes, M. persicolor and T. erinacei. The Yorkshire Terrier is predisposed to M.canis infection, the Jack Russell Terrier is predisposed to T. mentagrophytes and T. erinacei. In the cat dermatophytosis is principally caused by M. canis; the Persian appears to be at increased risk. Infection is by contact with infected animals or a contaminated environment. The incubation period is 1–3 weeks. Immunocompromised individuals are predisposed, including young and elderly animals.

Clinical Signs

Infection with M. canis presents with fine grey ‘ash-like’ alopecic lesions (Fig. 4.13); pruritus is minimal (Fig. 4.14). T. mentagrophtyes infection produces more severe inflammation with alopecia, crusting and in severe cases furunculosis. Lesions are usually well demarcated.

Figure 4.13 Well-circumscribed grey scaly lesions on the ear of a dog with ringworm.

Figure 4.14 Ringworm on ear of kitten.

Key Diagnostic Tests

• Trichography with hairs mounted in potassium hydroxide or lactophenol cotton blue.
  
• Fungal cultures taken with sterile toothbrush or carpet squares.

Yeast Infection

Aetiology and Pathogenesis

Malassezia yeasts are normal commensals of the canine and feline skin. Malassezia dermatitis is therefore usually secondary to an underlying condition. The West Highland White Terrier and Bassett (Fig. 4.15) appear to be over-represented. Young dogs with malassezia infection frequently have underlying allergy. Endocrine disease is more common in older dogs as an inciting factor. In cats malassezia is usually seen secondary to endocrine disease, especially hyperthyroidism. In the dog the majority of infections are caused by Malassezia pachydermatis. This yeast has also been implicated in the cat as well as M. sympodialis and M. furfur. Candida yeast is a rare cause of skin disease in the dog or cat.

Figure 4.15 Malassezia infection on the ear of a Bassett.

Clinical Signs

The ear pinna is erythematous and greasy with a yellow seborrhoeic appearance (Fig. 4.16), usually with a rancid, yeasty odour. In chronic disease the pinna becomes lichenified and hyperpigmented. Animals usually have a ceruminous otitis externa associated with signs on the ear pinna.

Figure 4.16 Malassezia on the ear flap of an allergic dog.

Key Diagnostic Tests

• Tape strippings, impression smears, cultures.

Leishmaniasis

Aetiology and Pathogenesis

Leishmaniasis is a rare disease in the United Kingdom but is common in Europe in dogs that live in or visit the Mediterranean basin. It is also found in southern Russia, India, China and eastern Africa. In the United States it has been identified in Oklahoma, Ohio and Texas. At least 30 different species have been identified in 5 different groups: L. donovani, L. major, L. tropica, L. aethiopica and L. mexicana. Leishmania is transmitted by blood-sucking sandflies (Phlebotomus spp. in Europe and Asia; Lutzomyia spp. in the Americas). Clinical signs can become apparent anything from 1 month to 7 years after exposure. It is rare in cats.

Clinical Signs

Clinical signs are very variable. Systemic signs can affect many different organs, and a full description is beyond the remit of this book. Cutaneous lesions affected 80% of dogs. The most common presentation on the ear pinnae is an exfoliative dermatitis with small adherent silvery scale (Fig. 4.17). Similar signs can be seen around the eyes, often referred to as periocular lunettes (Fig. 4.18). Dogs may also have nasodigital hyperkeratosis, nail disease, ulceration over pressure points, pustules, papules and nodules.

Figure 4.17 Scale on the ear flap of a dog with leishmaniasis.

Figure 4.18 Leishmaniasis in a dog showing generalized silvery scale.

Courtesy of Kevin Camilleri.

Key Diagnostic Tests

• Routine bloods: non-regenerative normochromic, normocytic anaemia, hypergammaglobulinaemia, hypoalbuminaemia.
  
• Organisms can be identified on cytology of scrapes or lymph node aspirates or from bone marrow or spleen.
  
• Histopathology: very variable pattern, organisms seen in 50% of cases with Giemsa stain.
  
• Leishmania-specific IgG detects presence of the organism but not necessary active disease.
  
• Polymerase chain reaction (PCR) highly sensitive.

4.2.2 Endocrine Disease

Hypothyroidism

Aetiology and Pathogenesis

In dogs approximately 90% of cases are due to primary hypothyroidism caused by the destruction of the gland. This is caused by lymphocytic thyroiditis or idiopathic thyroid necrosis and atrophy. Predisposed breeds include Labrador and Golden Retrievers, Dobermanns, Bearded Collies and Beagles.

Clinical Signs

Clinical signs are variable, affecting many different organ systems. Common cutaneous signs include bilateral symmetrical truncal alopecia, ‘rat tail’, seborrhoea, secondary bacterial pyoderma. Signs affecting the ear pinnae include none pruritic peripheral scaling (Fig. 4.19), alopecia (Fig. 4.20) or in some cases hypertrichosis.

Figure 4.19 Scaling on the periphery of an ear flap in a hypothyroid dog.

Figure 4.20 Alopecia and scaling on the ear flap of a hypothyroid dog.

Key Diagnostic Tests

• Blood samples: mild non-regenerative anaemia, elevations in cholesterol, ALT, AP and creatinine kinase.
  
• Thyroid function tests used in combination, as a single test is rarely diagnostic. A panel should include total T₄, freeT₄, thyroid stimulating hormone and thyroglogulin autoantibodies.

4.2.3 Environmental Disease

Actinic Change

Aetiology and Pathogenesis

Actinic skin damage is caused by prolonged exposure to ultraviolet light (UV). Lesions can affect the periocular, nasal and pinnal skin. Typically it is seen in elderly dogs and cats with white pinnae. Chronic damage can lead to the development of oncogenic change such as squamous cell carcinoma and haemangio/sarcoma.

Clinical Signs

Initial signs are of erythema and thickening of the pinnae with fine scaling (Fig. 4.21). Chronically the tips of the pinnae can become curled and scarred and cutaneous horn may develop. As neoplastic transformation occurs the ear pinna become ulcerated with marked proliferative changes.

Figure 4.21 Actinic change on a cat’s ear pinnae.

Key Diagnostic Tests

• Biopsy reveals signs of superficial fibrosis and follicular keratosis typical of actinic change

4.2.4 Keratinization Disorders

Primary keratinization disorders are very uncommon causes of skin disease in the dog and rare in the cat. However, when they occur the pinna is commonly affected and in some cases only the ear pinna is affected.

Primary Idiopathic Seborrhoea

Aetiology and Pathogenesis

Most commonly, but not exclusively, recognized in the Cocker Spaniel (Fig. 4.22). It is caused by an idiopathic increase in epidermal turnover. The transit time of cells from the basal cell layer to the stratum corneum is shortened to 7–8 days (normal dog 21 days).

Figure 4.22 Primary idiopathic seborrhoea in a Cocker Spaniel.

Clinical Signs

Affected dogs have thick greasy, adherent, yellowy/orange scale around the external ear canal extending on to the ear pinna. Follicular casts may be present on hairs. Animals tend to be malodorous and pruritic often with secondary infection with malassezia or pyoderma. Otitis externa is common. Chronically the ear canal can become lichenified (Fig. 4.23). Other areas that are involved include nipples, lip folds, ventral neck, trunk and feet.

Figure 4.23 Primary idiopathic seborrhoea in a Cavalier King Charles Spaniel.

Key Diagnostic Tests

• Predisposed breed.
  
• Biopsy only supportive, not diagnostic.
  
• Non-specific changes include a hyperplastic superficial perivascular dermatitis with ortho/parakeratosis, follicular keratosis and variable dyskeratosis.
  
• Other causes of seborrhoea must be eliminated.

Sebaceous Adenitis

Aetiology and Pathogenesis

Uncommon disease of unknown aetiology caused by loss of sebaceous glands. Theories include an autoimmune reaction against the glands or a primary structural defect of the gland leading to leakage of sebum and a foreign body reaction. Predisposed breeds include Standard Poodles, Akitas (Fig. 4.24), Vizslas and Samoyeds.

Figure 4.24 Sebaceous adenitis on the ear of an Akita.

Clinical Signs

Signs vary between breeds but lesions on the ear pinna usually take the form early on of scaling and thinning of the hair. There are usually prominent follicular casts around the base of the hairs (Fig. 4.25). Chronically the skin becomes more involved, with tightly adherent silver-white scale and tufted, matted hair. A dry ceruminous otitis externa with secondary infection is common.

Figure 4.25 Chronic sebaceous adenitis on the ear flap of a Labrador.

Key Diagnostic Tests

• Trichography reveals typical follicular casts. Multiple biopsies are needed.
  
• Early signs show a multifocal mixed inflammatory infiltrate (granulomatous–pyogranulomatous) around the sebaceous glands.
  
• Advanced cases have moderate acanthosis, hyperkeratosis and lack of sebaceous glands. Perifollicular granulomas are often found in the areas normally occupied by the sebaceous glands.

Ear Margin Seborrhoea

Aetiology and Pathogenesis

This is thought to be a primary keratinization defect of unknown aetiology that affects the margins of the ear. Dogs with pendulous ear pinnae appear to be predisposed, especially Dachshunds, Springer Spaniels and Cocker Spaniels.

Clinical Signs

Early signs are of excessive adherent keratinous debris accumulating along the margins of the ear (Fig. 4.26). Chronically, material can build up along the margins of the ears leading to fissuring.

Figure 4.26 Ear margin seborrhoea in a Cocker Spaniel.

Key Diagnostic Tests

• Clinical signs in a predisposed breed.
  
• Biopsy is supportive rather than diagnostic, showing signs of surface and follicular ortho/parakeratotic hyperkeratosis.
  
• Other differentials should be ruled out.

Exfoliative Cutaneous Lupus Erythematosus of the German Short-Haired Pointer

Aetiology and Pathogenesis

A possible hereditary disease of the German Short-Haired Pointer caused by an immune-mediated reaction against basal epithelial cells.

Clinical Signs

Signs are first recognized in young dogs of 5–8 months of age. Initially signs consist of scaling and thinning of the hair coat on the face, back and ears (Figs 4.27, 4.28). The disease can become generalized. Prominent follicular casting is seen with more diffuse scaling.

Figure 4.27 Exfoliative cutaneous lupus erythematosus in a German Short-Haired Pointer.

Figure 4.28 Exfoliative cutaneous lupoid erythematosus on the ear pinna of a German Short-Haired Pointer.

Key Diagnostic Tests

• Clinical signs in a predisposed breed.
  
• Biopsy reveals signs of ortho/parakeratotic hyper­keratosis, hydropic degeneration of basal cells and individual keratinocyte necrosis throughout the stratum corneum and a mixed cellular mild to moderate interface dermatitis.

Idiopathic Facial Dermatitis in Persian and Himalayan Cats

Aetiology and Pathogenesis

A disease of unknown aetiology. Some authorities suggest it may be a keratinization disorder involving the sebaceous glands. Age of onset is variable, ranging from 10 months to 6 years.

Clinical Signs

Accumulations of thick dark waxy debris is seen around the eyes, facial fold, chin and ears (Fig. 4.29). Cats commonly have a bilateral erythematous otitis with accumulations of black/brown debris on the ear pinna (Fig. 4.30). Secondary infection with yeast and bacteria is common and often leads to intense pruritus.

Figure 4.29 Idiopathic facial dermatitis in a Persian cat.

Figure 4.30 Ceruminous otitis in a Persian cat with idiopathic facial dermatitis.

Key Diagnostic Tests

• Clinical signs in a predisposed breed.
  
• Biopsy reveals acanthosis with superficial crusting. Hydropic degeneration of basal cells and occasional dyskeratotic keratinocytes especially in the follicular epithelium is seen, with sebaceous gland hyperplasia.

Zinc-Responsive Dermatoses

Aetiology and Pathogenesis

Zinc-responsive dermatosis occurs as a result of an impaired ability to utilize zinc. In type I disease, seen in the Siberian Husky and Alaskan Malamute, disease is caused by an inadequate absorption of zinc from the bowel. Type II disease is seen in fast-growing giant breed puppies which are fed an unbalanced diet. A relative deficiency of zinc occurs due to competition for absorption with zinc by high levels of cereal, calcium, copper or iron. Intestinal phytate and inorganic phosphate also bind zinc and hinder absorption.

Clinical Signs

Typically the ear pinna is erythematous and covered with fine silvery scale (Fig. 4.31). Dogs usually also have footpad hyperkeratosis and similar cutaneous lesions around the eyes (Fig. 4.32) and over pressure points. Pruritus is variable; secondary pyoderma is common.

Figure 4.31 Ear flap of a Husky with zinc-responsive dermatosis.

Figure 4.32 Husky with zinc-responsive dermatosis showing typical periocular lesions.

Key Diagnostic Tests

• Type I predisposed breeds, type II history of unbalanced diet.
  
• Tape stripping of skin reveals nucleated keratinocytes consistent with parakeratosis.
  
• Biopsy confirms acanthosis with diffuse parakeratosis.
  
• Response to therapy often diagnostic.

4.2.5 Miscellaneous

Psoriasiform–Lichenoid Dermatosis of the English Springer Spaniel

Aetiology and Pathogenesis

A scaling disease of the ear pinna of young English springer spaniels of unknown aetiology. The complete response that has been reported to cephalexin therapy suggest it may be an immune-mediated reaction to staphylococcus.

Clinical Signs

Characterized by erythematous papules and crusts with hyperkeratotic plaques on the concave aspect of the ear pinna. The external ear canal, head and ventral trunk may also be affected. Lesions may wax and wane with time, becoming more hyperkeratotic over several years, often assuming a papillomatous appearance chronically.

Key Diagnostic Tests

• Clinical signs and predisposed breed.
  
• Histopathology reveals a superficial perivascular to interstitial dermatitis with psoriasiform epidermal hyperplasia and areas of lichenoid interface dermatitis.

4.2.6 Neoplasia

Epitheliotropic Lymphoma

Aetiology and Pathogenesis

Most neoplastic diseases that affect the ear flap produce nodules, plaques or ulcers. However epitheliotropic lymphoma (EL) in the early stages of the disease can present with diffuse scaling. EL is caused by malignant transformation of T lymphocytes; atopic dermatitis is thought to be a risk factor in dogs. The neoplastic lymphocytes infiltrate the upper epidermis and dermis.

Clinical Signs

Dogs are usually elderly and scaling can affect the whole body. EL is a very pleomorphic disease : commonly dogs and cats present with a pruritic erythroderma with plaques of silver-white scale. The ear pinna in these cases is thickened and hyperkeratotic with plaques and ulceration (Fig. 4.33).

Figure 4.33 Silvery scale on the face and ears of a dog with epitheliotropic lymphoma.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. 8 SURGERY OF THE EAR
2. 1 ANATOMY OF THE EAR
3. 2 DIAGNOSTIC TECHNIQUES
4. 6 CONDITIONS OF THE MIDDLE EAR

Stay updated, free articles. Join our Telegram channel

Join