Lymphoma or histoplasmosis?

Ultrasonographic findings of gastrointestinal histoplasmosis in dogs

Erica Chávez-Peón Berle 1, Kate KuKanich 1, David Biller 1

Background
Histoplasmosis is a systemic mycotic infection caused by Histoplasma spp., which can present as a gastrointestinal disease in dogs, especially in endemic regions such as the Midwestern and Southern United States. Gastrointestinal histoplasmosis may mimic neoplasia on imaging due to overlapping sonographic features, yet its ultrasonographic characteristics have been underreported. This study aimed to describe the ultrasound findings associated with gastrointestinal histoplasmosis in dogs to better inform differential diagnosis and improve clinical evaluation.

Methods
This retrospective, single-center case series included 19 dogs diagnosed with gastrointestinal histoplasmosis between 2005 and 2020, confirmed by cytology or histopathology of the gastrointestinal tract or associated lymph nodes. All included dogs underwent abdominal ultrasound at the study institution. Stored ultrasound images were retrospectively reviewed by a veterinary radiologist and diagnostic imaging resident, who assessed gastrointestinal wall thickness, wall layering, lesion distribution, and lymph node characteristics. Clinical records were also reviewed for demographics, clinical signs, laboratory findings, treatment protocols, and outcomes.

Results
Eighteen of 19 dogs (94.7%) exhibited ultrasonographic abnormalities in the gastrointestinal tract, most frequently colonic thickening (up to 1.2 cm) and abnormal wall layering. Sixteen dogs (84.2%) showed altered or lost colonic wall layering; 56.2% had complete loss, while others had partial loss with submucosal thickening. Additional findings included small intestinal thickening, lymphadenopathy (63.1%), peritoneal effusion (42.1%), and various organomegaly. Histoplasma organisms were identified in some effusion samples. Most dogs (79%) received fluconazole, and 63.1% achieved clinical resolution, while two dogs continued to improve on treatment. Only two had follow-up ultrasound, both showing complete resolution of prior abnormalities.

Limitations
The small sample size, retrospective design, and inconsistent follow-up imaging limited the strength and generalizability of findings. Some diagnoses were based only on lymph node cytology and antigenuria rather than gastrointestinal histopathology, which introduces potential misclassification. Ultrasound technical parameters were not standardized or recorded, which may affect image interpretation and reproducibility.

Conclusions
The study identified that gastrointestinal histoplasmosis in dogs can present with ultrasound findings similar to neoplasia, particularly colonic wall thickening and altered wall layering. These overlapping features underscore the importance of confirmatory diagnostics such as cytology or histopathology. Clinicians in endemic regions should consider histoplasmosis as a differential for dogs with gastrointestinal signs and corresponding sonographic findings, as proper diagnosis can lead to effective antifungal treatment and favorable outcomes.

Disclaimer: The summary generated in this email was created by an AI large language model. Therefore errors may occur. Reading the article is the best way to understand the scholarly work. The figure presented here remains the property of the publisher or author and subject to the applicable copyright agreement. It is reproduced here as an educational work. If you have any questions or concerns about the work presented here, reply to this email.