Occurrence of Cutaneous Neoplasia in Dogs with Actinic Dermatitis in a Veterinary Medical Teaching Hospital - UFRGS, Brazil

Background: Actinic dermatitis is an environmental skin disease resulting from excessive exposure to ultraviolet light irradiated by the sun. This phototoxic reaction affects dogs and cats, particularly with short hair and lightly pigmented skin, exposed to sun light. Primary lesions are typical from a sunburn and chronic exposure, and may induce to a premalignant lesion known as actinic keratosis, which may develop to neoplasms. The aim of the present study was to describe a retrospective study of actinic dermatitis and the occurrence of cutaneous neoplasia in dogs presented to a Veterinary Medical Teaching Hospital (HCV/UFRGS) in Porto Alegre, Rio Grande do Sul, Brazil in a period of 10 years.Materials, Methods & Results: A retrospective review of medical records from January 2009 to December 2019 was performed to identify dogs with actinic dermatitis. Twenty-eight dogs were diagnosed based on a history of sun exposure and skin lesions including erythema, scaling, comedones, thickened skin, hyperpigmentation, ulceration and/or secondary infections on poorly pigmented skin. In addition, in twelve dogs (42.8%) the disease was also confirmed by histopathology. Cutaneous lesions locations were previously defined as head, limbs, neck and trunk. The head was subdivided in chin, ears, face, lips and nasal plane; the limbs in pelvic and thoracic; and the trunk, in abdomen, dorsal pelvis, perianal and thorax. All 28 dogs diagnosed with actinic dermatitis in the study had been chronically exposed to solar radiation and had light skin and coat. Dogs were between 3 and 20 years old, mean 7.6 years and median 7 years, mostly female dogs (64.2%) and neutered or spayed (64.2%). The most affected breeds were American Pitbull Terrier (35.7%) and Boxers (28.5%). Other breeds were Bull Terrier, Dalmatian, Dogo Argentino and Scottish Terrier. In 15 cases, tumors were confirmed by cytopathology or histopathology, resulting in 9 different skin tumors and two types of cysts (epidermoid and follicular). Among these, the most prevalent malignant neoplasm was squamous cell carcinoma (66.7%), followed by mast cell tumor (40%), hemangiosarcoma (26.6%), and basal cell carcinoma (6.6%). Five benign tumors were identified: hemangioma (13.3%), fibroma (6.6%), lipoma (6.6%), sebaceous adenoma (6.6%) and trichoepithelioma (6.6%). The most prevalent location for actinic lesions was the trunk (92.8%), being more prevalent on the ventral abdomen (82.1%). Actinic lesions were also present on head, neck and limbs. In 13/15 patients (86.6%), actinic lesions and at least one neoplasia location matched.Discussion: Actinic dermatitis tends to occurs in mid-aged to senile dogs because of the disease progressive and chronic behavior and owners delay to detect early clinical signs. In fact, actinic dermatitis was diagnosed at the average age of 7.6 years in the present study. The skin lesions were mostly located on light hair areas and were not observed on pigmented skin. The trunk (mainly the abdomen) had higher frequency of skin lesions compared to other anatomic areas, possibly because some dogs like to sunbathe at dorsal or lateral recumbency, some floor types can reflect sunlight, and some ventral abdomen are hairless. Ultraviolet radiation causes important local and systemic immunogenic changes. The impairment of the immune system and antigen recognition can influence cutaneous susceptibility to develop neoplasm. In conclusion, approximately 50% of the dogs with actinic dermatitis were associated with different skin neoplasm. The most prevalent was squamous cell carcinoma, mast cell tumor and hemangiosarcoma. Actinic lesions and neoplasm matched location in almost all patients with both conditions, however it was not possible to define if solar radiation had predisposed the occurrence of all observed neoplasms. Further studies are needed to prove the influence of ultraviolet radiation in the development of different cutaneous neoplasms.