Keratinization Defects

Chapter 50 Keratinization Defects



Kenneth W. Kwochka



PRIMARY DEFECTS OF KERATINIZATION


Primary defects of keratinization are dermatoses that are manifested clinically by localized or generalized excess scale formation. The scale may be formed from the interfollicular epidermis or may emanate from hair follicles as comedones and follicular casts. Histologically, the most striking abnormalities involve the keratinizing structures of the body including the epidermis, hair follicle outer root sheath, and hair cuticle.




Key Point


Cutaneous scaling of dogs is a very common clinical sign. In most cases, it is not due to a primary keratinization defect but is secondary to other dermatologic diseases. Common conditions causing secondary scaling include demodicosis, scabies, cheyletiellosis, atopic dermatitis, adverse food reaction (“food allergy”), flea allergy, pyoderma, yeast infection, dermatophytosis, hypothyroidism, hyperadrenocorticism, sex hormone abnormalities, pemphigus foliaceus, mycosis fungoides, and environmental influences. The veterinarian must determine whether the scaling is secondary to one of these conditions or associated with a primary keratinization defect. A primary keratinization defect is never diagnosed until the secondary causes of scaling have first been considered.


In this chapter, an overview of the etiology, clinical signs, diagnosis, and treatment of keratinization disorders is presented, followed by a description of each specific disease.



Etiology



• For most of the diseases classified as primary keratinization defects, the pathophysiology is unknown. For others, the cause is known and the primary pathophysiology involves a defect in the keratinizing epithelium or the cutaneous glandular function.


Clinical Signs



• Disorders of keratinization are characterized clinically by mild-to-severe dry, waxy, or greasy scales. Some degree of “seborrheic odor” may be associated with the skin condition. Because hair follicles and glandular structures may also be involved, it is not unusual to see comedones and follicular casts. Comedones are blackheads resulting from dilation of hair follicles with keratin plugs. Follicular casts are tightly adherent scales around hair shafts, giving the so-called candle wax appearance. Common secondary findings include alopecia, inflammation, crusts, pruritus with secondary excoriations, and pyoderma. Secondary Malassezia colonization may also be associated with primary and secondary causes of scaling, especially with greasy scales.



Key Point


Primary keratinization defects are usually hereditary and appear during the first 2 to 3 years of life. A breed incidence for these disorders is known. An observant owner usually indicates that the scaling was present before the development of secondary signs.



Diagnosis


No specific laboratory test exists for definitive diagnosis of a primary keratinization disorder. A combination of factors is used, including age of onset, breed, history, diagnostic elimination of more common secondary causes of scaling, findings on histologic examination of skin biopsies, and response to therapy.




Key Point


Skin biopsy is the most important diagnostic tool for primary keratinization defects (see Chapter 37). Biopsy results not only help make a definitive diagnosis but also help rule out dermatoses associated with secondary scaling.


Take several biopsies from lesions of various ages. Send samples to a veterinary pathologist who specializes in dermatopathology.



Treatment


After a definitive diagnosis of a primary keratinization defect is established, warn owners that the condition is most likely controllable but not curable.




Key Point


Some type of topical and systemic treatment will probably be needed for the remainder of the patient’s life.




Key Point


It is imperative to treat any secondary bacterial and/or yeast infections before a decision is made on the type of specific treatment that will be needed for the primary keratinization disorder.



PRIMARY IDIOPATHIC SEBORRHEA


Primary idiopathic seborrhea is the most common chronic keratinization disorder encountered in dogs. Predisposed breeds include cocker spaniels, English springer spaniels, West Highland white terriers, basset hounds, Irish setters, German shepherds, dachshunds, Doberman pinschers, Chinese Shar-Peis, and Labrador retrievers.



Etiology



• In cocker spaniels and Irish setters, at least part of the pathophysiology of scale formation involves hyperproliferation of basal epidermal keratinocytes.



Key Point


Many dogs with primary idiopathic seborrhea will have concurrent dermatoses that contribute to the severity of the cutaneous scale and inflammation.


For example, it is not unusual to see a seborrheic cocker spaniel with concurrent allergic dermatosis and secondary pyoderma and/or yeast dermatitis. When these conditions are diagnosed and treated properly, the remaining scale caused by the primary seborrhea is much less severe and easier to control.



Clinical Signs



• Depending on the breed, clinical signs may range anywhere from dry scaling (seborrhea sicca), to greasy scaling (seborrhea oleosa), to scaling and greasiness with inflammation and pruritus (seborrheic dermatitis), and any combination of these clinical abnormalities on the same animal. Breeds affected with the seborrhea sicca form of idiopathic seborrhea include Doberman pinschers, Irish setters, German shepherds, and dachshunds. Breeds most predisposed to the seborrhea oleosa form include cocker spaniels, English springer spaniels, basset hounds, West Highland white terriers, Chinese Shar-Peis, and Labrador retrievers.


Diagnosis



• A definitive diagnosis of primary idiopathic seborrhea requires a number of different supporting factors, including age of onset, breed, history, diagnostic elimination of secondary causes of scaling, and findings on histopathologic examination of skin biopsy specimens.

• The most important aspect of the diagnostic plan is a full investigation for secondary causes of scaling. The primary differentials are allergic dermatitis, scabies, dermatophytosis, demodicosis, bacterial folliculitis, Malassezia dermatitis, hypothyroidism, and vitamin A–responsive dermatosis. Additional differentials in Doberman pinschers are color-dilution alopecia and adult-onset follicular dysplasia.

• Biopsy samples are usually characterized by orthokeratotic and parakeratotic hyperkeratosis, follicular hyperkeratosis, and dyskeratosis. Often, the follicular abnormalities are more impressive than are the changes in the surface epidermis.


Treatment



Topical Therapy



• As in most primary keratinization disorders, the treatment goal in primary idiopathic seborrhea is to control scale formation, not to cure the disease. Moisturize the skin and haircoat when dry scaling is present. This task is accomplished with twice-weekly moisturizing hypoallergenic shampoos (HyLyt EFA, DVM Pharmaceuticals; Allergroom, Virbac; Micro Pearls Advantage Hydra-Pearls, EVSCO) and frequent moisturizing rinses (HyLyt EFA Bath Oil Coat Conditioner, DVM Pharmaceuticals; Humilac, Virbac) after each shampoo.

• When dry scaling is severe and some keratolytic activity is needed, the treatment usually consists of sulfur and salicylic acid shampoos (SebaLyt and SeboRex, DVM Pharmaceuticals; Sebolux, Virbac; Micro Pearls Advantage SebaMoist and SebaHex, EVSCO) followed by moisturizing rinses. Dietary supplementation with an omega-6 and omega-3 essential fatty acid combination is also beneficial (e.g., DermCaps, DVM Pharmaceuticals).

• Use keratolytic and keratoplastic degreasing shampoos to control the scale and odor associated with seborrhea oleosa. Effective topical agents include coal tar (NuSal-T, DVM Pharmaceuticals; T-Lux, Virbac; LyTar, DVM Pharmaceuticals; Allerseb-T, Virbac), benzoyl peroxide (OxyDex and Sulf OxyDex, DVM Pharmaceuticals; Pyoben, Virbac; Micro Pearls Advantage Benzoyl Plus, EVSCO), and selenium sulfide (Selsun Blue, Ross). If significant bacterial and/or yeast infections are playing a major role in the greasy scaling dermatitis, it is better to use an antibacterial and antifungal shampoo combination (Malaseb Shampoo, DVM Pharmaceuticals; KetoChlor Shampoo, Virbac) alone or alternated with one of the keratolytic degreasers.


Systemic Therapy



• The synthetic retinoid etretinate (Tegison, Roche) had been effective for idiopathic seborrhea in cocker spaniels, springer spaniels, Irish setters, golden retrievers, and mixed-breed dogs at 1 mg/kg PO q24h. Etretinate has been replaced by acitretin (Soriatane, Roche) at a dosage from 0.5 to 1.0 mg/kg PO q24h. Response is seen within 2 months and consists of decreased scale, odor and pruritus, and softening and thinning of seborrheic plaques. Some dogs have been maintained without signs of toxicity over several months on alternate-day therapy.



Key Point


The synthetic retinoids are associated with teratogenicity. Do not use in breeding animals, and warn clients about the serious potential risks from accidental human ingestion. Other potential side effects include keratoconjunctivitis sicca; leg and joint pain; and mild elevations in cholesterol, triglycerides, and liver enzyme levels. These are usually reversible on discontinuation of therapy or lowering the dosage. Perform Schirmer tear tests and liver panels every 2 to 4 weeks initially and then every 3 months during maintenance therapy. Unfortunately, the synthetic retinoids are prohibitively expensive for most owners.



• Calcitriol (Rocalcitrol, Roche) has been effective for idiopathic seborrhea in cocker spaniels at 10 ng/kg PO q24h. Give the medication as far removed as possible from the main meal of the day to decrease the possibility of hypercalcemia. Response is seen within 2 to 3 months. Continue treatment for life with monitoring of calcium and parathyroid hormone levels.

• Cyclosporine (Atopica, Novartis) at a dosage from 5 to 10 mg/kg PO q24h has been effective for some dogs with severe idiopathic seborrheic dermatitis. It is suspected that these dogs may be those with a strong allergic component to their disease.

• A 7- to 10-day course of prednisone or prednisolone at an anti-inflammatory dose may occasionally be needed during periods of severe inflammation and pruritus in dogs with seborrheic dermatitis.


VITAMIN A–RESPONSIVE DERMATOSIS


Vitamin A–responsive dermatosis is a rare, nutritionally responsive scaling disorder of primarily cocker spaniels. Similar syndromes have been reported in other breeds, including miniature schnauzers, Labrador retrievers, and Chinese Shar-Peis in Europe.



Etiology


This condition is not a systemic vitamin A deficiency but probably represents a local deficiency in the epidermis, a problem with uptake in the skin, a disorder of cutaneous utilization, or a positive pharmacologic effect of high doses on the epidermis.



Clinical Signs



• Vitamin A–responsive dermatosis has clinical signs consisting of refractory generalized scaling, dry haircoat with easy epilation, prominent comedones, and hyperkeratotic plaques with large “fronds” of keratinous material protruding from the follicular ostia. The plaques are usually on the ventral and lateral thorax and abdomen, but the neck and face may also be involved. Other clinical features include a rancid odor from the skin, ceruminous otitis externa, and varying degrees of pruritus. Gordon setters have a dorsal pruritic papular dermatitis that responds partially to antibiotic treatment, but relapses without vitamin A supplementation.


Diagnosis



• Vitamin A–responsive dermatosis is characterized clinically by an early age of onset of refractory generalized scaling with ventral follicular hyperkeratosis and hyperkeratotic plaques with large “fronds” of keratinous material protruding from the follicular ostia in cocker spaniels. Gordon setters have a dorsal pruritic papular dermatitis that responds partially to antibiotic treatment but relapses without vitamin A supplementation.

• The major diagnostic differentials for this condition include primary idiopathic seborrhea, zinc-responsive dermatosis, generic dog food dermatosis, sebaceous adenitis, and superficial necrolytic dermatitis.

• A more definitive diagnosis can be made with skin biopsy findings consisting of marked follicular hyperkeratosis and very distended follicular ostia, mild orthokeratotic hyperkeratosis of the epidermis, and mild irregular epidermal hyperplasia. Even with classic clinical and histologic findings, a definitive diagnosis can be confirmed only by response to supplementation with vitamin A.


Treatment



• Treat patients with vitamin A–responsive dermatosis with 625 to 800 IU/kg PO q24h of vitamin A. Improvement is seen within 4 to 6 weeks, complete remission is obtained by 10 weeks, and treatment is needed for life. Vitamin A at this dosage is well tolerated in dogs; therefore, no clinicopathologic monitoring is necessary. Keratolytic shampoos containing benzoyl peroxide have excellent follicular flushing activity. Twice-weekly treatment helps remove keratinous debris from follicles and hastens recovery.

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  3. Immune-Mediated Dermatoses
  4. Canine and Feline Demodicosis

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Keratinization Defects

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