Solar dermatitis in a cynomolgus macaque (Macaca fascicularis)

Chronic exposure to ultraviolet (UV) light can cause cutaneous damage, resulting in specific pathological changes such as actinic keratosis and dermatitis. Despite actinic dermatosis being well documented in both humans and animals, it has rarely been reported in non-human primates (NHPs). Here, we describe a case of chronic UV light exposure in cynomolgus macaque (Macaca fascicularis). An adult female was presented with a seven-month history of multifocal irregular alopecic, erythematous and hyperkeratotic plaques on the dorsum with itching. Skin biopsies were sampled for histopathological analysis. A biopsy of normal skin from the neck region of an adult macaque was used as a control. Histopathological analysis revealed epidermal changes ranging from moderate to marked hyperplasia associated with hyperkeratosis and mild stratification disorders. Fibrosis was observed in the upper dermis, and multiple areas of elastotic material deposition were confirmed in the mid and deep dermis by Van Gieson special staining. The diagnosis was "solar dermatitis with elastosis". Systemic treatment with nutritional supplements (retinol and omega-3) and firocoxib (5 mg/kg orally once a day for 3 months) did not show any improvement. Concurrently, a topical therapy with aloe gel and a sunscreen spray (SPF50) was added. The lesions did not show further clinical progression. During the period of the study, two other cynomolgus macaques from the same enclosure developed comparable clinical lesions on the dorsum. The authors describe UV-light induced skin damage in a cynomolgus macaque, which remained clinically stable.