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Primary & Secondary Keratinization Disorders

Sandra Sargent, DVM, DACVD Pittsburgh Veterinary Specialty & Emergency Center Pittsburgh, Pennsylvania

Photo courtesy of Keith A. Hnilica, DVM, MS, DACVD, MBA

The opposite, seborrhea oleosa, refers to YOU HAVE ASKED ... greasy skin and hairs.1 Many patients, What is the difference between however, have both flaky and greasy primary and secondary skin; thus, although these terms are descriptive, they may not be particularly keratinization disorders? helpful, as the conditions can be caused by a large number of underlying diseases. THE EXPERT SAYS ... Physicians use the term seborrheic der- Chronic seborrheic skin disease is matitis to refer to a chronic inflamma- aesthetically displeasing and can tory disorder affecting areas of the head adversely affect the human–animal and trunk where, in humans, sebaceous bond. Nonspecific descriptive terms glands are prominent.2 Veterinary cli- such as seborrhea oleosa, seborrhea sicca, ents may be frustrated when they pres- and seborrheic dermatitis are commonly ent their pet for seborrhea treatment used to describe sebhorrhea, but there and are told that seborrhea is rarely a is confusion around these terms. In specific diagnosis but simply a descrip- veterinary medicine, seborrhea sicca is tive term. They may fail to understand used to describe focal or diffuse scaling of why a detailed history, examination, the skin with the accumulation of white and further testing are necessary to nonadherent scales and a dull dry coat. determine the underlying cause.

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When treating a patient with scaly or sebor- 80% of all seborrhea cases; it is critical to rule rheic skin, it is important to determine out such secondary disorders before diagnos- whether the scaling is a primary keratiniza- ing primary keratinization dermatoses.4 tion defect or secondary to another skin or internal disease. In primary keratinization Most cases of secondary seborrhea have a good disorders, the excessive scale is caused by a prognosis if the underlying cause is identified direct defect in one or more steps in stratum and treated successfully. Primary keratiniza- corneum formation. Secondary disorders (ie, tion diseases are more difficult to control and those in which seborrhea develops as a result usually require lifelong management, which is of another condition3) account for at least often labor intensive and costly.

TABLE 1 Secondary Disorders Because they are common, secondary sebor- 5 CAUSES OF SECONDARY SEBORRHEA IN DOGS rheic disorders (Table 1) should be an imme- diate consideration on initial examination. Multiple conditions often occur simultane- Cause Clinical Examples ously, and almost every dermatologic disor- der can result in seborrheic signs. Infectious Pyoderma Dermatophytosis A good dermatologic history discloses age of Malassezia spp dermatitis onset, seasonality, presence of pruritus, and Leishmaniasis whether any other pets or humans in the Allergic Flea allergy dermatitis household are affected. Because diseases of Atopy other body systems can cause these dermato- Food hypersensitivity ses, the clinician should inquire whether Contact dermatitis other abnormalities such as polyuria, poly- Endocrine Hypothyroidism dipsia, polyphagia, heat-seeking behavior, Hyperadrenocorticism appetite changes, or weight gain or loss have been observed. Parasitic Scabies Physical examination of the skin and other Cheyletiellosis Pediculosis systems can provide many clues for diagno- sis. A minimum dermatologic database (eg, Nutritional Dietary imbalance skin scrapings, impression cytology, fungal Malabsorption, maldigestion culture) should be collected. Secondary bac- Fatty acid deficiency terial infections should be identified by rec- Immune-mediated Pemphigus foliaceus ognizing lesions caused by infection (eg, Systemic lupus erythematosus papules, pustules, epidermal collarettes) and Cutaneous drug reactions by sampling these lesions for microscopy. Sebaceous adenitis

Metabolic Superficial necrolytic dermatitis Identified infections should be treated with appropriate oral and/or topical therapy. In Neoplastic Cutaneous epitheliotropic lymphoma older patients or those with signs consistent with internal disease, a CBC, serum chemistry Environmental factors Low environmental humidity profile, and thyroid hormone panel are import- Excessive bathing, overgrooming ant in ruling out internal secondary causes.

84 cliniciansbrief.com April 2017 Primary Disorders lar plugging or casts is highly suggestive, True keratinization defects (Table 2) are although other causes (eg, hypercortisolism, much less common in dogs and even more sebaceous adenitis, demodicosis) can cause rare in cats; therefore, this discussion will similar changes, and secondary infections can focus on canine diseases. Many primary complicate diagnosis. Diagnosis is confirmed keratinization disorders are hereditary, so via biopsy and response to treatment with affected animals should not be bred.3 Vitamin A (ie, retinol).1

Primary canine seborrhea has long been con- sidered an inherited disorder of keratiniza- Ichthyosis is a congenital skin disease charac- tion; it is most commonly recognized in the terized by excessive hyperkeratosis on all skin American cocker spaniel, English springer surfaces, including pads. Ichthyosis has been spaniel, West Highland white terrier, and bas- recognized in a variety of breeds, including the set hound.1 Diagnosis can often be compli- golden retriever, West Highland white terrier, cated because many of these breeds are also American bulldog, Jack Russell terrier, Nor- commonly affected with allergic skin disease.1 folk terrier, and Cavalier King Charles spaniel.1

A recent study questioned whether primary Most of these patients are obviously abnor- seborrhea is a true entity.3 As the role of mal at birth or soon thereafter; however, in Malassezia pachydermatis and staphylococcal the golden retriever, lesions can be subtle and infections have become more widely recog- may not be recognized until adulthood.6,7 nized, many cases that would have been Large sheets of scale are seen on the hair labeled primary seborrhea in the past are shafts, and large adherent scales are seen on now recognized as pyoderma, M pachyderma- sparsely haired skin. The diagnosis can be tis dermatitis, allergic dermatitis, or seba- confirmed by biopsy and, in some breeds, ceous adenitis. Primary seborrhea may be an adaptive response rather than a true keratini- zation defect, and primary seborrhea may not TABLE 2 be considered a true entity.3 PRIMARY KERATINIZATION DEFECTS4 If the more common causes of secondary seb- orrhea are ruled out and/or the signalment and history are consistent with a primary Cause Clinical Examples disorder, the following diseases, which result in similar clinical signs and can be easily Congenital, Primary seborrhea confused, should be carefully considered: hereditary Ichthyosis Follicular parakeratosis Vitamin A-Responsive Dermatosis Schnauzer comedo syndrome Footpad hyperkeratosis This disorder is described primarily in the Hereditary nasal hyperkeratosis in Labrador retrievers cocker spaniel, although it has also been reported in the Labrador retriever, miniature Other Vitamin A-responsive dermatoses schnauzer, and Gordon setter.3 It is character- dysplasia ized by an adult-onset seborrheic skin disease Nasodigital hyperkeratosis Feline acne with significant follicular plugging and casts Canine ear margin dermatoses as well as hyperkeratotic plaques. Ceruminous Tail gland hyperplasia otitis is also common. The pronounced follicu-

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genetic testing.* Allergic skin disease is also liculitis should be controlled with antibiotic common in these breeds, further complicat- therapy.1 The condition is lifelong, but most ing diagnosis and treatment. cases can be controlled with chronic mainte- nance therapy. Clients should be counseled that ichthyosis is incurable and can be difficult to manage, Ear Margin Dermatosis especially in more severely affected dogs. Ear margin dermatosis is characterized by Many golden retrievers are more mildly subclinical, bilaterally symmetrical keratini- affected, and, although the worst aspect for zation disorder confined to the ear margins. It owners is a cosmetically displeasing skin and is most commonly seen in .8 Vary- coat, this breed is at higher risk for secondary ing amounts of scale are found along the edge skin infections. Topical treatments and fatty of the pinna. Follicular casts (ie, accumulation acids remain the treatment of choice for all of keratinous debris around the hair shaft forms of ichthyosis.3 seen protruding from the follicular ostium or present when hairs are plucked and exam- Schnauzer Comedo Syndrome ined) may be prominent, and the underlying Schnauzer comedo syndrome is a follicular skin appears uninflamed. The condition typi- keratinization defect occurring exclusively cally occurs at an early age and waxes and in miniature schnauzers1; it is seen more wanes chronically with or without treatment. commonly in young adults and is character- If the ear margins are intensely pruritic, sar- ized by crusting and multiple waxy comedones coptic mange should be considered. If more located along the dorsal midline of the dog. severe crusting, ulceration, or fissures are The underlying cause is thought to be an inher- present, vasculitis should be considered and ited developmental defect in the hair follicle biopsies may be necessary for a definitive diag- that results in abnormal keratinization with nosis. Because patients with ear margin der- subsequent comedone formation, follicular matosis are typically subclinical, treatment plugging, and secondary bacterial .1 may not be necessary, and aggressive treat- Most affected dogs will respond to keratolytic ment may worsen the condition.8 If desired, and follicular flushing agents (eg, benzoyl the scale and hair casts can be removed and peroxide shampoo). Secondary bacterial fol- kept at a minimum via application of topical keratolytic or moisturizing agents. A topical *Genetic testing for ichthyosis is available for golden retrievers product containing phytosphingosine has (Optigen; optigen.com) and American bulldogs (University of Pennsylvania; vet.upenn.edu). been reported to be helpful.1 n

References 1. Miller WH, Griffin CE, Campbell KL. Muller and Kirk’s Small Therapeutic Guide. 3rd ed. St. Louis, MO: Elsevier Saunders; Animal Dermatology. 7th ed. St. Louis, MO: Elsevier Mosby; 2011:21. 2013. 6. Cadiergues MC, Patel A, Shearer DH, Fermor R, Miah S, 2. Johnson BA, Nunley, JR. Treatment of seborrheic dermatitis. Hendricks A. Cornification defect in the golden retriever: Am Fam Physician. 2000;61(9):2703-2710. clinical, histopathological, ultrastructural and genetic 3. Mauldin EA. Canine Ichthyosis and related disorders characterisation. Vet Derm. 2008;19(3):120-129. of cornification. Vet Clin North Am Small Anim Pract. 7. Mauldin EA, Credille KM, Dunstan RW, Casal ML. The clinical 2013;43(1):89-97. and morphologic features of nonepidermolytic ichthyosis in 4. Foster A, Foil C. BSAVA Manual of Small Animal Dermatology. the golden retriever. Vet Pathol. 2008;45(2):174-180. 2nd ed. Gloucestershire, UK: British Small Animal Veterinary 8. Scott DW, Miller WH. Canine ear margin dermatosis: a Association; 2003. retrospective study of 10 cases (1988-2012). Jpn J Vet 5. Hnilica KA. Small Animal Dermatology: A Color Atlas and Dermatol. 2013;19(4):225-227.-

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