Granular cell tumours are uncommon soft tissue neoplasms believed to arise from Schwann cells. Oral, ocular and neurological forms have been reported in dogs, and various locations including the gastrointestinal tract have been reported in humans. This latter location has not been reported in dogs.

A four-year-old female neutered Jack Russell Terrier presented with one-year history of haematochezia and intermittent diarrhoea that did not respond to dietary changes, and antibiotics. On presentation, the dog was bright and alert and in good body condition. Rectal examination revealed multiple (>20) nodular masses (approximately 3–4 mm in diameter) in the rectum. The remainder of the examination was unremarkable.

Bloodwork revealed hypocobalaminaemia (138 pmol/L, reference range 200–408) and hypofolataemia (6.7 nmol/L, reference range 12–30) consistent with diffuse small intestinal disease. Haematology and biochemistry were unremarkable. A gastrointestinal endoscopy documented multiple small masses in the rectum and the colon (>50 in total). These masses were present on the last 20 cm of the large intestine. The mucosa around the masses appeared irregular and swollen. The ileum appeared mildly irregular. Histopathology of the masses identified a population of large cells with granular cytoplasm multifocally expanding the lamina propria between the glands, consistent with granular cell tumours. There was also a mild aggregation of lymphocytes, plasma cells and sparse eosinophils in the colic mucosa between the masses. There was minimal lacteal dilation in the ileum, with no evidence of inflammation. Additional stains did not yield significant information. Bacterial and fungal cultures of colic biopsies were negative.

Diet change to a hypoallergenic diet (Purina HA) and parenteral cobalamin supplementation led to resolution of the diarrhoea. At the most recent follow-up one year after diagnosis, the dog was still clinically well on hypoallergenic diet. The owners reported intermittent haematochezia and very occasional tenesmus. Rectal examination was similar to the initial visit.

Granular cell tumours are uncommon and predominantly benign neoplasms in humans; 10% of the tumours develop in the gastrointestinal tract. Endoscopic surveillance is usually sufficient for small and asymptomatic tumours. Surgical excision is recommended for large, malignant and multifocal tumours. Endoscopic resection has also been recently reported. No surgical excision was attempted in our dog given the multiplicity of the masses and the absence of significant clinical signs. To our knowledge, this is the first description of multiple granular cell tumours affecting the gastrointestinal tract in dogs, and these appeared to have a benign clinical course.

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