Reduce sun exposure
The main treatment recommendation for solar dermatitis is restricting sun exposure by keeping the dog indoors during the day,
especially between 9 a.m. and 3 p.m., which is considered the most intense UV radiation time.2 If some sun exposure is unavoidable, then frequent (twice a day11) topical application of a waterproof, high-SPF sunscreen (a product with an SPF > 15 absorbs more than 92% of UVB rays12 ) that is labeled as safe for babies and that protects against UVA and UVB rays is indicated.2 Having the dog wear a T shirt may help decrease sun exposure2; however, it is often impossible to cover all at-risk areas of the skin. A dog sun suit is available at
http://www.designerdogwear.com/, or clients may be able to sew a sun suit for their pets by using sun-blocking fabric available for people.
Beta-carotene or acetretin
To decrease sun damage, beta-carotene (30 mg orally b.i.d. for 30 days then 30 mg/day for life) in combination with anti-inflammatory
doses of oral glucocorticoids may be effective in early cases.2,13 Skin damage may also be reduced by administering oral retinoids (synthetic vitamin A analogues, which are more potent and
less toxic than vitamin A2,14 ) such as acitretin at a dosage of 0.5 to 1 mg/kg orally every 24 hours.2 The potential side effects of retinoids include keratoconjunctivitis sicca, mucocutaneous lesions, vomiting, diarrhea, musculoskeletal
abnormalities, triglyceride elevations, and hepatotoxicity,2,11 so careful monitoring is necessary. Additionally, retinoids are highly teratogenic.2 A positive clinical response to retinoids should be noted within four to six weeks. At that point, the frequency of medication
can be reduced to an alternate-day basis.11
Because of the expense of retinoids, oral vitamin A has been used anecdotally for canine solar dermatitis, but controlled
clinical trials and published studies elucidating doses or side effects are not available. The dosage of oral vitamin A in
dogs should not exceed 400 IU/kg/day, and patients should be monitored for the same potential side effects as listed for retinoids.2
Actinic keratosis in people may be helped by using a topical immunomodulator such as imiquimod (Aldara—3M Pharmaceuticals),
but studies in dogs are lacking. Imiquimod's mechanism of action involves inducing local antitumor and antiviral immune responses
by stimulating lymphocytes, dendritic cells, and macrophages. In people, imiquimod cream is applied to affected areas two
to three times a week for four to 16 weeks.15-18 According to the Aldara package insert, the size of the treated area should be no larger than 2 x 2 in, and the cream should
not be used near the eyes, lips, or nostrils. The cream is left on the skin for eight hours before being washed off with mild
soap and water. Side effects include localized redness, crusting, burning, and pruritus at the site of application. In dogs
with more extensive lesions of solar dermatitis, the expense of Aldara (about $245 for a box of 12 individual 250-mg single-use
packets) may preclude its use.
Monitor for disease progression
Even with future sun avoidance, prior skin damage can still progress to skin neoplasia months or years after exposure (Figure 7). Once skin neoplasia has occurred, aggressive surgical resection or laser therapy should be performed. In addition, if large
or invasive masses are present, screening for metastasis to draining lymph nodes and internal structures is necessary.
7. The same dog as in Figures 1 and 6 after six weeks of antibiotic therapy and three months of sun avoidance. Although scarring
is still present, the prior lesions of erythema and bullae have resolved. However, note the persistent scaly, erythematous
erosive lesion on the prepuce, which is likely a precancerous or early cancer lesion. A biopsy is indicated.