Discussion:
Visceral mast cell tumours are uncommon in dogs and the prognosis is extremely poor. The primary tumour can arise from the spleen, liver or gastrointestinal tract. Clinical signs, as in this case progress rapidly and contribute to the short survival time. In dogs, disseminated mast cell neoplasia often occurs secondary to a cutaneous mast cell tumour. There was no evidence of a cutaneous tumour in this dog at the time of diagnosis, but recent history included excision of a tumour from the base of the tail. This mass had been confirmed as an haemangioma but only a section of the tumour had been submitted. It is possible that the section submitted was not representative of pathology in other parts of the mass and this may have in fact been a cutaneous mast cell tumour.

Mast cell tumours can be associated with a paraneoplastic syndrome, which results in gastroduodenal ulceration. Paraneoplastic syndromes are defined as tumour-associated clinical signs, which occur distant to the tumour. Mast cell tumours release excess histamine, which stimulates gastric H2 receptors and result in increased acid secretion. In this case gastroduodenal ulceration was not confirmed using histopathology but the dog had clinical signs of gastrointestinal ulceration (melaena and haematemesis). It was suspected that the nasal discharge reported in this case was due to GI haemorrhage with aspiration into the respiratory tract.