Disorders of Keratinization

Primar y Idiopa thic Seborrhea

Ceruminous otitis can be due to an inherited or acquired keratinization defect. Inherited disorders include idiopathic primary seborrhea, commonly seen in West Highland White Terriers, American Cocker Spaniels, English Springer Spaniels, Basset Hounds, Irish Setters, Dachshunds, Chinese Shar-Peis, and German Shepherds.

The epidermis of the canine ear canal undergoes proliferation, differentiation, and desquamation with renewal of the viable epidermis in approximately 22 days. In American Cocker Spaniels that have idiopathic primary seborrhea, the proliferative, differentiative, and desquamative stages take an average of 8 days. This rapid turnover of epidermal cells increases the renewal stage that produces seborrhea (manifested as seborrheic dermatitis, ceruminous otitis, or both). This defect in differentiation includes hyperkeratosis or hypokeratosis and dyskeratosis.

Clinical Signs. The clinical signs of primary and secondary ceruminous otitis are the same and can only be diagnosed on the basis of response to therapy. In-depth clin­ical and diagnostic evaluations are mandatory for animals that present with chronic ceruminous otitis. These animals usually present with other primary or secondary dermatologic manifestations.

Clinical signs can be mild or chronic, with secondary bacterial or Malassezia infections complicating the primary problem. Ears with ceruminous otitis are malodorous, and there is often secondary epidermal hyperplasia of the ear canal and pinna that may occlude the auditory meatus.

In the author’s experience, animals with moist vertical canals due to pendulous ears and poor ventilation are presented more often with chronic ceruminous otitis that requires general anesthesia for proper ear examination. Examination under general anesthesia allows the clinician to visualize thoroughly, clean, and obtain biopsy specimens from the ear.

A biopsy is often necessary to differentiate chronic epidermal hyperplasia with chronic ceruminous otitis from ceruminous gland tumors. Secondary bacterial and Malassezia infections respond when the underlying cause is properly treated. If there is no response, evaluation should consist of bacterial and fungal culture and sensitivity testing.

Diagnosis. Histologic evaluation of noninfected seborrheic areas usually supports a diagnosis of primary seborrhea. After identification of secondary invaders and appropriate medical management, diagnosis is most frequently confirmed by response to treatment.

Treatment. Because ceruminous otitis is only the manifestation of a more seri­ous problem, finding the underlying cause should be the clinician’s primary goal. Treatment of primary seborrhea should attempt to control the disease rather than produce a complete cure. Treatment of the ears should focus on (1) control of secondary infections and of production of scales and crust, and (2) reduction of inflammation. Frequent ear cleaning with appropriate topical medication can control the odor associated with this condition. Steroids, cytotoxic drugs, and retinoic acid have variable effects. Results with the use of synthetic retinoid (etretinate) in Cocker Spaniels and other breeds to treat idiopathic seborrhea are disappointing. In the Cocker Spaniel, for example, there is a reduction of scales, crust, and alopecia, but the ceruminous otitis is not responsive to this therapy.

Endocrine Dermatosis

The most common endocrine diseases associated with ceruminous otitis are hypothyroidism and hyperadrenocorticism.

Hypothyroidism. Breed predilections for hypothyroidism include Golden Retrievers, Alaskan Malamutes, Chow Chows, Boxers, English Bulldogs, Chinese Shar-Peis, Great Danes, Afghan Hounds, Doberman Pinschers, Newfoundlands, Dachshunds, and Cocker Spaniels. Hypothyroidism in cats is extremely rare.

Etiology. The causes of hypothyroidism are classified as primary, secondary, tertiary, and congenital. Examples of causes of primary hypothyroidism include lymphocytic thyroiditis, thyroid atrophy, thyroid gland hyperplasia, neoplasia, and thyroid cell destruction due to radioactive iodine treatment or antithyroid drug therapy. Secondary hypothyroidism in the dog is the result of pituitary destruction and malformation or suppression of thyrotropic cell function. There are no known causes of canine tertiary hypothyroidism. Defects in iodine organification and thyroid gland dysgenesis are the two most common causes of congenital hypothyroidism in the dog.

Clinical Signs. Thyroid hormone is an important regulator in the body’s meta­bolic function. A deficiency causes a decrease in the normal cellular metabolic func­tions of the body. The clinical signs of hypothyroidism in the dog are extremely variable, being those of metabolic, dermatologic, reproductive, neuromuscular, ocular, gastrointestinal, cardiovascular, hematologic, and behavioral disorders.

Serum and cutaneous fatty acid concentrations are affected by thyroid hormones. Thyroid hormones stimulate the synthesis, mobilization, and degradation of lipids, with the most dramatic effect being a decrease in degradation. This may present as an increase in serum low-density lipoprotein (LDL).

Thyroid hormone increases the sebum production necessary for the normal lipo- genesis and synthesis of sterol by keratinocytes and increases cutaneous linoleic acid, with a decrease in gamma linolenic and arachidonic acid concentrations.

Secondary bacterial and Malassezia infections are complicating factors in ceru­minous otitis and can be a dermatologic nightmare if not treated properly. Other dermatologic abnormalities in dogs with hypothyroidism are myxedema, thin skin, hyperkeratosis, seborrheic ear pinnae, pyoderma, symmetrical or patchy endocrine alopecia, and various degrees of hyperpigmentation. Otic pruritus is often present with secondary bacterial or Malassezia infection.

Diagnosis and Tireatment. The resolution of the ceruminous otitis largely depends on the proper diagnosis and control of hypothyroidism. History and physical exami­nation findings are important in the diagnosis of hypothyroidism. A complete blood count, serum biochemistry profile, urinalysis, and thyroid stimulation test are some of the few laboratory tests used to diagnose hypothyroidism.

Because the availability of thyroid-stimulation hormone is limited due to factors of price and supply, in most cases the interpretations of total tetraiodothyronine (T4), free T4, and thyroid-stimulating hormone (TSH) in combination with clinical manifesta­tions are the only diagnostic tools at the clinician’s disposal. For this reason, it is impor­tant to note that misdiagnosis of this disease can be easily made if the appropriate tests are not performed. Drugs such as glucocorticoids, anticonvulsants, trimetoprim/ sulfamethoxazole, phenylbutazone, quinidine, salicylates, and radiocontrast agents can adversely affect thyroid levels in the body. It is recommended that these medications be withdrawn, if possible for up to 2 weeks, before a thyroid test is performed.

Epidermal hyperplasia and pain often occur in the treatment of ceruminous otitis. Topical steroid preparations are useful in controlling pain and inflammation and reducing epidermal hyperplasia. Because steroids affect baseline thyroid levels, thyroid profiles should be performed before or 1 or 2 weeks after discontinuing any topical otic medications with steroids.

Hyperadrenocorticism. Bilateral adrenocortical hyperplasia due to pituitary adenoma is the most common cause of hyperadrenocorticism in the dog. The excessive production of cortisol by the adrenal gland results in systemic as well as dermatologic abnormalities. The prolonged exogenous use of oral, intramuscular, or intravenous (and possibly otic and ophthalmic) corticosteroids may also cause iatrogenic hyper- adrenocorticism. Other causes are adrenal adenomas and carcinomas.

The cutaneous manifestations of excessive serum cortisol are as follows:

• Alopecia

• Failure or slowness of hair growth after clipping

• Thin skin

• Pyoderma

• Seborrhea

• Comedone formation

• Bruising

• Striae formation

Seborrhea dermatitis may manifest as ceruminous otitis with secondary bacterial or Malassezia infections.

Glucocorticoids inhibit epidermal proliferation and sebum production through antimitotic, protein-catabolic, and antienzymatic effects. The decrease in hair growth is manifested clinically through bilateral symmetrical or “moth-eaten” alopecia. The antimetabolic and antiproliferative effects on fibroblasts are evident as poor wound healing. There is also an increase in susceptibility to infections. Because animals with hyperadrenocorticism show signs of secondary hypothyroidism, clinical signs of seborrhea and skin infection may be exaggerated due to the dermatologic effects of low thyroid levels.

The combination of seborrhea and bacterial or Malassezia infections can be manifest as ceruminous otitis, which is not as common in the cat as in the dog.

Diagnosis and Tireatment. Diagnosis of hyperadrenocorticism is based on history, complete blood count, serum biochemistry, urinalysis, adrenocorticotropic hormone (ACTH) stimulation test, low- or high-dose dexamethasone suppression tests, and ultrasonographic and radiographic findings. Because steroids affect thyroid levels, a thyroid stimulation test, if available, or a thyroid profile (T4, free T4 [ED], and TSH) is part of the diagnostic plan. However, a thyroid profile should be performed after hyperadrenocorticism has been diagnosed and controlled to mini­mize the adverse effects of steroids outlined previously. Treatment of otitis externa secondary to hyperadrenocorticism depends on proper diagnosis and treatment of the hyperadrenocorticism. Any secondary bacterial or Malassezia infection should also be treated.

Several factors are important in the treatment of hyperadrenocorticism. Most animals with this disease are presented with other problems such as a secondary bacterial, parasitic (Demodex), or fungal skin infection, as well as otitis. When these are encountered, individual treatment modalities are recommended for each specific problem. Therefore, in treating an animal with hyperadrenocorticism, secondary problems can complicate the picture, making therapy prolonged and complicated at times.

Other Endocrine Dermatoses. Other causes of endocrine dermatosis include Sertoli cell tumors, seminoma, interstitial cell tumor, estrogen-responsive dermatoses, and hyperandrogenism in intact male dogs.