Obstructive colonic FGESF associated with feline infectious peritonitis in a cat: a case report.

backgroundFeline infectious peritonitis (FIP) is a severe immune-mediated disease that develops in a small proportion of cats infected with feline coronavirus (FCoV). Clinical manifestations are variable and most commonly involve systemic inflammatory disease with or without effusion. Gastrointestinal signs, including vomiting or diarrhea, may be observed; however, focal intestinal lesions leading to mechanical obstruction are rare. Histopathologic changes resembling feline gastrointestinal eosinophilic sclerosing fibroplasia (FGESF) have only rarely been reported in association with FIP. CASE PRESENTATION: A 6-month-old Scottish Fold cat was evaluated for vomiting, constipation, weight loss, and jaundice. Abdominal radiography, ultrasonography, and contrast-enhanced computed tomography identified an approximately 80 mm segment of marked transmural thickening of the distal descending colon resulting in mechanical obstruction. Surgical resection was performed. Histopathologic examination of the excised segment revealed a dense fibroinflammatory lesion characterized by marked eosinophilic infiltration, reactive spindle-shaped fibroblasts, and prominent collagen trabeculae, consistent with an FGESF-like process. Immunohistochemistry demonstrated intracytoplasmic feline coronavirus antigen within macrophages in the resected tissue. Feline coronavirus RNA was also detected in peripheral blood by reverse-transcription polymerase chain reaction. TREATMENT AND OUTCOME: The affected colonic segment was resected with end-to-end anastomosis. Postoperative management included supportive care, antimicrobial therapy, corticosteroids, nutritional support via an esophagostomy tube, and antiviral treatment with GS-441,524. Antiviral therapy was initiated by subcutaneous injection and subsequently continued orally for a total duration of 12 weeks. Progressive clinical improvement was observed, including resolution of gastrointestinal signs and jaundice, weight gain, and improvement in clinicopathologic abnormalities during follow-up.

conclusionsThis case describes an uncommon presentation of non-effusive FIP associated with a colonic FGESF-like fibroinflammatory lesion causing mechanical obstruction. FIP should be considered among differential diagnoses for eosinophilic intestinal masses in young cats, even in the absence of effusion. Integration of histopathology with molecular diagnostic techniques, including lesion-based immunohistochemistry, may support diagnostic evaluation in atypical cases. Early recognition and etiology-directed management may contribute to favorable short-term outcomes.