Diagnosis and treatment of solar dermatitis in dogs - Veterinary Medicine
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Diagnosis and treatment of solar dermatitis in dogs
Skin damage from the sun in dogs can be easily mistaken for other skin diseases. Make sure you and your clients are aware of the signs and are doing everything possible to prevent this potentially serious condition.


VETERINARY MEDICINE



5. Solar dermatitis on the inguinal area of an American bulldog. After years of sun damage, a large squamous cell carcinoma has formed.
The duration and intensity of sun exposure influence the degree of skin damage. The initial signs of actinic damage are erythematous, scaly lesions, which may be tender. With repeated sun exposure, actinic folliculitis, follicular cyst formation, and dermal fibrosis occur.8 In dogs with pigmented areas on their skin, there is often sharp demarcation between areas of normal skin with protective pigment and damaged nonpigmented skin (Figure 2).2 With chronic sun exposure, damaged areas become thickened and scarred with comedones, erosions, ulcers, crusts, and draining tracts.2 Secondary bacterial pyoderma is common.9 Sun-induced skin tumors such as squamous cell carcinoma (Figure 5), hemangioma, and cutaneous hemangiosarcoma may occur. Although affected dogs may lick damaged areas, the pruritus associated with solar dermatitis is usually otherwise minimal, unlike that in dogs with allergic dermatitis. However, some dogs can have solar dermatitis and concurrent allergies.

DIAGNOSIS

Diagnosing solar dermatitis involves considering a patient's signalment and clinical signs and ruling out other causes of scaly, erythematous dermatitis or folliculitis (e.g. bacterial, Demodex species, and dermatophyte infections). Lack of resolution of skin lesions with empiric therapy should raise your suspicion of solar dermatitis and the need for further investigation.


6. Inguinal erythema, scarring, and furunculosis caused by chronic sun damage in the same dog as in Figure 1. The circled areas indicate biopsy sites.
Ultimately, skin biopsy and histology are used to diagnose solar dermatitis and solar-induced neoplasia. Depending on the degree of secondary bacterial infection, systemic antibiotics may be indicated for two to three weeks before biopsy to ensure that infection does not alter histologic interpretation. Additionally, clearing secondary skin infection also increases the likelihood of correctly selecting solar-induced rather than infection-induced skin lesions for biopsy.10 However, if an obviously neoplastic skin mass is noted on physical examination, perform a biopsy immediately to expedite treatment. Biopsy can be performed by administering lidocaine locally and obtaining multiple skin punch or excisional biopsy samples of different lesions (Figure 6).

Since some of the histologic changes can be seen with other conditions such as bacterial folliculitis, one key to a definitive histologic diagnosis is to include a complete history with the biopsy submission form, including signalment, degree of sun exposure, distribution of lesions, clinical description of lesions, response or lack of response to prior therapies, and current medications (including glucocorticoids) that could affect the histologic findings. Requesting a full histologic description and seeking interpretation by a veterinary dermatopathologist are recommended.

In early cases of solar dermatitis, histologic examination shows variable degrees of perivascular dermatitis, folliculitis, and dermal fibrosis or increased collagen accumulation or collagen damage. Solar elastosis (linear bands of degenerated basophilic elastin accumulation arranged parallel to the skin surface) may be seen. In chronic cases, histologic examination may show follicular cysts, pyogranulomatous inflammation, and precancerous actinic keratosis or neoplastic cells.2,9,10

TREATMENT

The best treatment for canine solar dermatitis is prevention. Educate owners of at-risk dogs about the need for sun avoidance starting at a young age. Also tell owners of affected and at-risk dogs that oral and topical medications cannot replace sun avoidance in treating and preventing solar dermatitis.


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Source: VETERINARY MEDICINE,
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