Equine sun-induced dermatoses
Abstract
Photodermatitis is a commonly encountered skin condition in the horse in the summer months. This article explains the difference between phototoxicity and photosensitization and reviews the different dermatoses present in each condition. Pastern and cannon leukocytoclastic vasculitis is a less common cause of dermatitis affecting the lower limbs of the horse that has been associated with exposure to strong sunlight.
Electromagnetic radiation is composed of a continuous spectrum of wavelength of which ultraviolet (uv) light is of particular importance in precipitating or potentiating a number of skin lesions. This article focuses on the two main subdivisions of photodermatitis, namely phototoxicity and photosensitivity which are of primary concern to the veterinary surgeon. Pastern (and cannon) leukocytoclastic vasculitis is a specific disease of the equine skin that often occurs in the summer and has been associated with strong sunlight exposure (Stannard, 2000).
Phototoxicity is the classic sunburn reaction and is a dose-related response to light exposure. White skin, depigmented or scarred areas are most susceptible especially if there is poor hair covering (Figures 1 and 2). The pathogenesis is not fully understood but involves damage to the epidermis and blood vessels of the deep plexuses. In severe cases, secondary crusts may form and it may become very painful. Topical treatment with emollients and topical glucocorticoids is usually sufficient after removing from sunlight.
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