The clinical challenges of the equine periorbital sarcoid

The equine sarcoid affects horses of all ages, types, and colours without obvious sex predilection and is commonly encountered worldwide. It is by far the commonest equine skin neoplasm (Jackson, 1936; Thomsett, 1979; Pascoe and Summers, 1981; Genetzky, Biwer and Myers, 1983; Marti, Lazary and Gerber, 1993; Broström, 1995). Although the sarcoid has been recognised for centuries (Erk, 1976), it was first characterised by Jackson in 1936. He defined the sarcoid as “a unique locally invasive, benign neoplastic like tumour of the skin with a variable epidermal component which has a high propensity for recurrence.” The name sarcoid (meaning flesh-like) was used to emphasise the clinical and pathological differences from papilloma, fibroma, and fibrosarcoma and to suggest the malignant sarcomatous appearance of the lesions. Pathologically the equine sarcoid has been categorised as a benign tumour of fibrous tissue (Hendrick and others, 1998). The periocular skin is a recognised predilection site (Knottenbelt, 2009) (Figure 1).