Actinic Dermatoses and Sun Protection

Chapter 116

Actinic Dermatoses and Sun Protection

Solar-induced lesions in dogs and cats occur on skin with no or light pigmentation and sparsely haired regions that are exposed frequently to sun. Lesions are more common in dogs and cats that spend substantial time outdoors or sunbathe (lying in dorsal or lateral recumbency for extended periods), or are housed where there is reflective ground cover (including snow) and little sun protection. The most commonly affected dog breeds are white English bull terriers, dalmatians, beagles, fox terriers, whippets, white boxers, American Staffordshire bull terriers, basset hounds, and American bulldogs. White-haired areas of short-haired cats are most at risk. Blue-eyed white cats are most susceptible.

Clinical Features of Actinic Dermatoses in Dogs and Cats

Canine Disease

In dogs lesions range from patchy or confluent erythema and scaling affecting nonpigmented thickened skin to scaly erythematous papules or crusted indurated linear plaques and nodules with erosions and ulcers and hemorrhagic crusts. Actinic comedones may be present, filled with darkly colored keratinous or caseous debris in nonpigmented lightly haired skin and may be irregularly thickened and firm on palpation. Lesions may be discrete pigmented subepidermal foci or small nodules. Comedones may rupture, eliciting a foreign body response and furunculosis. Intact hemorrhagic bullae are a distinctive feature secondary to actinic comedone rupture with crusted erythematous nodules that may be intact or fistulated. A coexistent bacterial pyoderma may make the clinical diagnosis more difficult.

Actinic keratoses are premalignant epithelial lesions that can transform into invasive squamous cell carcinoma. These lesions are either single or multiple and are erythematous, scaly red to reddish-brown, ill-defined macules that progress to indurated, crusted plaques and are rough on palpation. Induration, erosion, ulceration, or increasing diameter should raise the suspicion of evolution into squamous cell carcinoma. Lesions often are found abruptly adjacent to normal pigmented skin. In dogs that sunbathe lesions commonly are observed on the glabrous skin of the ventral and lateral abdomen, flank folds, inner thighs, scrotum, and perineum. The hock and distal hind limb, bridge of the nose, pinnae, dorsal muzzle, periorbital regions, and tail tip also may be affected.

Diagnosis of Actinic Dermatosis

The diagnosis of actinic dermatitis is based on the correlation of breed, coat color, coat length, ultraviolet (UV) light exposure, and lesion localization to body sites commonly affected by solar damage. Comedones in sun-exposed skin, with or without evidence of other solar-induced lesions, should increase suspicion of actinic dermatosis. The lesions of actinic furunculosis need to be differentiated from deep bacterial folliculitis and furunculosis, demodicosis with deep pyoderma, systemic or opportunistic fungal infections, and neoplasia.

Actinic dermatitis is diagnosed by histopathologic analysis. It is important to resolve any secondary infections before collection of biopsy samples. Biopsy specimens should be obtained from different types of lesions and different stages of the disease. A complete history should be provided with the biopsy submission, including signalment, degree of solar exposure, and distribution and clinical description of lesions, and the specimens should be examined by a veterinary dermatohistopathologist if possible. Characteristic microscopic lesions include vacuolated keratinocytes with pyknotic nuclei and eosinophilic cytoplasm (“sunburn cells”), epidermal hyperplasia, follicular keratosis, laminar alteration of collagen in the superficial dermis (dogs) with superficial laminar fibrosis, perivascular to lichenoid inflammation, solar elastosis, and actinic comedones with pyogranulomatous folliculitis and furunculosis as common sequelae to comedonal rupture.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Actinic Dermatoses and Sun Protection

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