Another Frenchy disease?

Idiopathic Intestinal Smooth Muscle Hyperplasia in a French Bulldog: Clinical, Imaging, Capsule Endoscopy, and Histopathological Findings

Hyomi Jang 1, Sang-Woo Kim 2, Joon Woo Lee 2, Munso Kim 2, Dong-In Jung 2

Background
Idiopathic intestinal smooth muscle hyperplasia (IISMH) is a rare, non-neoplastic condition characterized by proliferation of smooth muscle layers in the gastrointestinal tract. It differs from inflammatory or neoplastic intestinal diseases and has been scarcely reported in veterinary literature. The pathogenesis is poorly understood, though similar conditions have been described in various species, including humans. This report documents the diagnostic process, treatment, and outcome of a French Bulldog with confirmed IISMH.

Methods
A 3-year-old female French Bulldog with chronic diarrhea, vomiting, hyporexia, and weight loss underwent a diagnostic workup including blood tests, abdominal ultrasonography, and capsule endoscopy. These revealed ileal wall thickening with muscular hypertrophy and partial luminal obstruction. Differential diagnoses included neoplasia and chronic inflammatory conditions. Surgical resection and anastomosis were performed from the distal ileum to the ileocecal junction, including full-thickness biopsies for histopathology. Postoperatively, the dog received anti-inflammatory medication (prednisolone), antibiotics (tylosin), and dietary management.

Results
Ultrasound and capsule endoscopy revealed marked muscular layer thickening and a partially obstructive lesion in the distal ileum. Histopathology confirmed smooth muscle hyperplasia with no mucosal invasion, no neoplastic features, and only mild inflammatory infiltration of macrophages, neutrophils, and lymphocytes. The lesion was classified as idiopathic. Over one year of follow-up, the dog showed significant clinical improvement with increased body weight and only occasional diarrhea. Mild residual muscular thickening persisted on imaging.

Limitations
Immunohistochemical staining was not performed, which would have helped definitively rule out gastrointestinal stromal tumors. Advanced infectious disease testing and nutritional absorption assessments were also not conducted due to cost constraints. Interobserver variability in imaging and lack of parasite screening were additional limitations. The lack of a standardized protocol for the management of IISMH in dogs restricts generalizability.

Conclusions
This case illustrates that idiopathic intestinal smooth muscle hyperplasia can be a distinct cause of chronic gastrointestinal symptoms in dogs, mimicking neoplastic or inflammatory diseases. Accurate diagnosis requires advanced imaging and histopathological confirmation. Surgical resection combined with medical and dietary management can lead to favorable clinical outcomes. Further studies are needed to clarify the etiology and optimal treatment strategies for this rare condition.

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