Hyperplastic and Seborrheic Syndromes in Animals

Many anomalies affect keratinization; some are associated with hereditary hypotrichoses, whereas others are associated with systemic metabolic derangements. A diverse group of syndromes for which none of these associations have yet been made may affect localized parts of the epithelium or may be generalized. Among the latter are poorly characterized congenital or familial seborrheic syndromes, the best known of which are idiopathic seborrhea of Spaniels and idiopathic facial dermatitis of Persian cats.

Hereditary congenital follicular parakeratosis is a syndrome of female Rottweilers and Siberian Huskies. It is a severe keratinization defect associated with various noncutaneous abnormalities.

Cutaneous ichthyoses are characterized by abnormal and hypertrophic epithelial proliferation, with accumulation of extensive scale and hyperkeratosis on the skin surface (see image of ichthyosis in a dog). Cases have been described mostly in cattle and dogs; however, chicken and several mouse models are also known, and there is one report in a llama. In cattle, severity varies; some forms are lethal shortly after birth. Affected breeds include Red Poll, Friesian, Holstein, Brown Swiss, Pinzgauer, and Chianina.

Ichthyosis, dog

Image

Courtesy of Dr. Karen A. Moriello.

Canine ichthyosiform dermatoses are also heterogeneous and occur sporadically in several dog breeds, including Doberman Pinschers, Rottweilers, Irish Setters, Collies, English Springer Spaniels, Cavalier King Charles Spaniels, Golden Retrievers, Labrador Retrievers, American Bulldogs, and terriers (including Parson Russell Terriers). There is some evidence of a familial inheritance pattern in Parson Russell Terriers and Golden Retrievers. Gene variants have been identified in the following breeds:

• Golden Retriever (pnpla1)

• American Bulldog (nipal4)

• Shar Pei (krt1)

• Great Dane (slc27a4)

• Jack Russell Terrier (tgm1)

• German Shepherd Dog (asprv1)

In affected dogs, the body is covered with large adherent scales that may flake off in sheets. The nasal planum and digital pads may be markedly thickened in some forms; thickened pads are usually associated with apparent discomfort.

Congenital linear hyperkeratosis is a disorder of keratinization most common in Quarter Horses. No treatment exists, and the disorder is primarily cosmetic. It can be managed with good coat hygiene and emollients (see congenital linear hyperkeratosis image).

Congenital linear hyperkeratosis, horse

Image

Courtesy of Dr. Karen Moriello.

Clinical management is difficult; however, clinical signs may be ameliorated with keratinolytic shampoos or solutions (eg, selenium disulfides, lactic acid, and benzoyl peroxide) and with humectants (eg, lactic acid, urea, propylene glycol, and essential fatty acid preparations). Experimental use of synthetic retinoids has been helpful. Control of secondary pyoderma is frequently required.

Nasal parakeratosis of Labrador Retrievers is a hereditary condition characterized by marked accumulations of thick keratinized material on the dorsal nasal planum and is typically first noticed when dogs are young (see nasal parakeratosis image). It is associated with a gene mutation in suv39h2.

Diagnosis is based on clinical signs; definitive diagnosis is via skin biopsy. Nasal parakeratosis is a longterm condition that can be managed but not cured. Treatment should include emollients (eg, topical agents typically containing glycerin, hyaluronic acid, propylene glycol, and urea).

Nasal parakeratosis, Labrador Retriever

Image

Courtesy of Dr. Karen A. Moriello.

Psoriasiform-lichenoid dermatosis affects young English Springer Spaniels and is presumed to be genetic. The erythematous, symmetrical lesions, which consist of papules and plaques on the pinnae and inguinal region, are covered with scales and become increasingly hyperkeratotic if not treated. In some affected dogs, lesions can eventually spread, and skin is severely greasy. Spontaneous remissions and a waxing and waning course are recorded. Some dogs respond to antimicrobial treatment or to synthetic retinoids (eg, isotretinoin, 1 mg/kg, PO, every 12 hours, with food until clinical remission and then transition to lowest possible dose); however, most are refractory to treatment. Modified cyclosporine A (5 mg/kg, PO, every 24 hours, longterm) has been used with mixed results in some dogs.

Pityriasis rosea of pigs is a familial disease in which the mode of inheritance is not known. Dermatosis vegetans of Landrace pigs is a hereditary, possibly congenital, disorder with an autosomal recessive mode of inheritance. It must be differentiated in the early stages from pityriasis rosea. Dermatosis vegetans is a more serious disease and affects hooves as well as skin. Lesions begin as macules and papules and are scaly, as in pityriasis rosea. Lesions later become covered with brown-black crusts and are associated with coronitis and hoof deformity. Affected piglets fail to thrive, develop pneumonia, and may die; affected survivors are stunted. No effective treatment exists.

Familial footpad hyperkeratosis is reported in Irish Terriers and Dogues de Bordeaux. Several gene variants (dsg1, fam82g, krt16) have been identified in this cluster of disorders. All footpads are involved from a young age, although the disease is not usually congenital. When hyperkeratosis is severe, horns, fissures, and secondary infection cause pain and lameness. No other skin lesions are present.

Treatment for familial footpad hyperkeratosis is supportive, with soaking, keratolytic and emollient treatments, and treatment of bacterial pyoderma. Synthetic retinoids have been used for some disorders of keratinization in dogs; however, for this disorder, no reports are available. Major differential diagnoses for footpad hyperkeratosis include hepatocutaneous syndrome, keratinization disorders, and pemphigus.

Sebaceous adenitis is an idiopathic disease that destroys the sebaceous glands and, in some dog breeds, is associated with severe seborrheic and alopecic dermatosis. The exact cause is unknown and is likely multifactorial. It is hereditary in Standard Poodles and suspected to be familial in Akitas, Vizslas, Springer Spaniels, and Havanese. The disease also affects adult rabbits.

Sebaceous adenitis first manifests itself in young adults, but inapparent carriers are known in Poodles. Marked hyperkeratosis precedes development of hair coat abnormalities, which begin as loss of normal hair kinkiness and progress to patchy alopecia. Akitas tend to have more seborrhea oleosa and less alopecia than Poodles.

Response to treatment is inconsistent and incomplete. Topical treatment benefits affected individuals. Mildly affected dogs are treated with antiseborrheic shampoos (typically containing coal tar, salicylic acid, and micronized sulfur) and as needed for pyoderma. Severely affected dogs benefit from propylene glycol or warm oil treatments massaged into their hair, left on for 1–6 hours, and then washed off to remove the oil. Treatments are repeated every 7–30 days.

Some dogs respond to oral supplementation with omega-3 fatty acids (110 mg EPA/68 mg DHA, PO, every 24 hours, longterm) or synthetic retinoids (isotretinoin 1 mg/kg, PO, every 24 hours). Note, however, that isotretinoin causes severe birth defects and must not be used in pregnant or breeding dogs. Pregnant women or women trying to become pregnant should handle this drug only with gloved hands, if at all.

Spontaneous remission has been recorded but is uncommon. The most commonly used and effective systemic treatment for sebaceous adenitis is modified cyclosporine A (5 mg/kg, PO, every 24 hours, lifelong). Up to 16 weeks of treatment may be required to see maximum benefit.