Oesophageal pythiosis in dogs: an uncommon clinicopathological presentation

The epidemiological, clinical and anatomopathological findings of oesophageal pythiosis in two dogs in northeastern Brazil are described. During the study period, 7696 canine tissue samples were evaluated, of which 33 cases of pythiosis were diagnosed (31 intestinal and two oesophageal), with oesophageal involvement accounting for 0.03% of all samples and 6.1% of pythiosis cases. The first dog was a 3-year-old female American Pit Bull Terrier, which was referred with a 2-month history of dysphagia, salivation, regurgitation, weight loss and swelling in the ventral aspect of the cervical region. The second dog was a 3-year-old female mixed breed dog, which was referred with a 30-day history of anorexia, dysphagia, constant salivation, regurgitation, polydipsia and weight loss. Necropsies revealed firm light-yellow multinodular masses extending longitudinally through the oesophageal wall, involving the cervical to mid-oesophagus in case 1 and the middle to distal third in case 2, with a transmural fistulous tract in the latter. Histologically, granulomatous inflammation and necrosis, with intralesional hyphae that failed to stain with haematoxylin and eosin, were observed. Immunohistochemistry (IHC) for Pythium insidiosum revealed strong immunolabelling of the hyphae. The diagnosis of pythiosis was based on the epidemiological, clinical and anatomopathological findings, and confirmed by IHC. Oesophageal pythiosis should be considered as a differential diagnosis in dogs with chronic digestive clinical signs. Histological evidence of granulomatous inflammation associated with unstained hyphae may represent an important diagnostic clue and should prompt further investigation by microbiological, immunohistochemical or molecular methods.