Primary Cornification Disorders in Dogs

Chapter 114


Primary Cornification Disorders in Dogs



The term cornification (keratinization) refers to the process by which epidermal cells undergo terminal differentiation from basal keratinocytes to the highly specialized corneocytes. Traditionally, disorders of cornification have been divided into those with primary and those with secondary causes. In primary cornification disorders, the excessive scale is due to a direct defect in one or more steps involved in the formation of the stratum corneum. Some authors include abnormalities of sebaceous gland function (e.g., sebaceous adenitis, sebaceous gland dysplasia) as primary cornification disorders as well. Secondary disorders are those in which excessive scaling develops as a result of another condition such as fleabite hypersensitivity, sarcoptic mange, hypothyroidism, or epitheliotropic lymphoma. More than 80% of scaling disorders arise from secondary causes.


Primary disorders of cornification are generally diagnosed by ruling out secondary causes. The signalment, age of onset, and presence or absence of pruritus aid in the formation of differential diagnoses and determination of the diagnostic approach. In a standard veterinary practice, a minimal dermatologic data set (e.g., skin scrapings, acetate tape preparations, impression smears, trichograms, dermatophyte culture) along with routine blood work can effectively rule out secondary disorders. Skin biopsies are often needed to establish a definitive diagnosis. Primary cornification disorders are generally nonpruritic and arise in young animals. These disorders have strong breed predilections; however, it should be kept in mind that spontaneous mutations can arise in any breed or mixed-breed animal.



Ichthyosis


In veterinary medicine, the term ichthyosis has been limited to rare congenital or hereditary disorders believed to be due to primary defects in the formation of the stratum corneum. A skin biopsy is invaluable in establishing a definitive diagnosis. For breeding dogs, molecular testing may be needed to further characterize the defect and identify carrier dogs.




Nonepidermolytic Ichthyosis


Nonepidermolytic ichthyosis in golden retrievers appears to be common, relatively mild, and unique in its variable presentation and onset. An autosomal-recessive mode of inheritance has been shown. Affected dogs develop large, soft, white to gray adherent scale that is prominent on the trunk and may be associated with ventral hyperpigmentation. A definitive diagnosis can be achieved by skin biopsy. Histologically, affected dogs have diffuse lamellar orthokeratotic hyperkeratosis in the absence of epidermal hyperplasia and dermal inflammation. Dogs are typically diagnosed at younger than 1 year of age; however, adult-onset cases are not uncommon. Some dogs develop secondary bacterial folliculitis, which may lead to pruritus. The disease may wax and wane with periodic bouts of exacerbation and remission.


Nonepidermolytic ichthyosis has been characterized in American bulldogs at the author’s institution. Unlike golden retrievers, bulldogs consistently develop clinical signs before weaning. Extensive pedigree analysis suggests an autosomal mode of inheritance. Young puppies have a disheveled hair coat compared with normal littermates. In puppies as young as 1 to 2 weeks of age, the glabrous skin becomes erythematous with tightly adherent brown scale, which gives the abdominal skin a “wrinkled” appearance. The remainder of the pelage has widely distributed large white scale. Malassezia overgrowth may be severe. In the absence of yeast infection, the histologic features are similar to those seen in the golden retriever. The development of otitis externa, intertrigo, and pododermatitis corresponds with the yeast proliferation and the onset of pruritus. In adult dogs, this clinical presentation can be easily confused with atopic skin disease. Occasionally adult dogs may have footpad hyperkeratosis. Unlike in golden retrievers, the skin lesions in bulldogs do not wax or wane and are generally more severe.


Nonepidermolytic ichthyosis in Jack Russell terriers appears to be less common and has a more severe phenotype than that in golden retrievers and American bulldogs. Affected dogs have large, thick, adherent parchment paper–like scales that have the histologic appearance of marked, tightly laminated, orthokeratotic hyperkeratosis. The dogs develop severe Malassezia infections.


A congenital and autosomal-recessive form of keratoconjunctivitis sicca with scaling has been documented in cavalier King Charles spaniel dogs. The dogs have a syndrome that includes the following features: keratoconjunctivitis from the time the eyelids open, roughened curly pelage, scaling with abdominal hyperpigmentation, footpad hyperkeratosis, nail dystrophy, and periodic nail sloughing.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Primary Cornification Disorders in Dogs
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