Introduction
The most common clinical signs of paraneoplastic syndromes in horses include hypercalcemia, hypoglycemia, cachexia, intermittent fever, anemia, thrombocytopenia, neutrophilia, protein losing enteropathy, vasculitis and pruritus (Axiak and Johnson 2011, Knottenbelt et al. 2015). Long before the tumour is clearly identified, paraneoplastic pruritus is often the main or only clinical sign observed, which can make early and accurate disgnosis of such pathologies very difficult. (Knottenbelt et al. 2015). Such pruritus can be accompanied by alopecia, which can be as a consequence of paraneoplastic changes or by self-mutilation (Knottenbelt et al. 2015). Skin biopsies and scrapings are often inconclusive or nonspecific and can be confused with the consequences of self-trauma (Knottenbelt et al. 2015). There is some evidence that pruritus as a consequence of neoplasia is caused by the destruction of T-cells arising from pathological cytokines produced by the tumour itself or the tumour’s growth, nerve compression, bile duct compression with cholestasis or necrotic tumourous cells (Knottenbelt et al. 2015). Paraneoplastic pruritus has been described in horses with lymphoma (Finley et al. 1998), mast cell tumours (Combarros et al. 2020) and renal carcinomas (Curnow 2020).
Despite the fact that pruritus is reported as one of the relatively more common equine paraneoplastic clinical signs, there is a little clinical evidence to support it.
In this article, we would like to document a case whereby persistent pruritus was the only clinical sign in a horse suffering from paraneoplastic pruritus caused by malignant round cell tumours. Publications in equine oncology are few, and documentation of such cases such are necessary to aid and assist practitioners in achieving more expediated and correct diagnosis of such conditions