Ultrasonographic findings of gastrointestinal histoplasmosis in dogs

Histoplasmosis, a mycotic infection caused by Histoplasma spp, can infect the gastrointestinal tract of dogs. Clinical signs of gastrointestinal histoplasmosis can include diarrhea, profound weight loss, anorexia, and vomiting. Rectal scrape for cytology can provide a quick diagnosis, but if negative abdominal ultrasound is often pursued. Ultrasonographic abnormalities in dogs with gastrointestinal histoplasmosis have rarely been reported. This retrospective, single-center case series aimed to describe the ultrasonographic features of gastrointestinal histoplasmosis in dogs. Nineteen cases with a diagnosis of gastrointestinal histoplasmosis confirmed with gastrointestinal cytology or histopathology (N = 15) or gastrointestinal lymph node cytology (N = 4) that had undergone an abdominal ultrasound examination from 2005 to 2020 were included. Ultrasound images were reviewed by an American College of Veterinary Radiology (ACVR)-certified veterinary radiologist and diagnostic imaging resident. Eighteen cases had sonographic abnormalities within the gastrointestinal tract. The colon was the most affected organ. Colonic thickening and abnormal wall layering were the most frequent findings (N = 16 dogs); thickening ranged from 0.36 to 1.2 cm. Diffuse, multifocal, and focal thickening patterns were seen. Sixteen patients had abnormal wall layering of the colon (complete loss of layering or altered with partial loss of layering). Other frequent findings included lymphadenopathy, small intestinal thickening with abnormal wall layering and peritoneal effusion. Based on the authors’ review of the literature, this is the first description of ultrasonographic findings of gastrointestinal histoplasmosis in a group of dogs. Although abnormal gastrointestinal wall layering seen sonographically is most frequently associated with neoplasia, this is not pathognomonic. Gastrointestinal histoplasmosis should be considered as a differential diagnosis due to the similarities and overlap of ultrasonographic features.