Small cell lymphoma or enteritis in the cat: where to biopsy
12-year-old neutered domestic shorthair with progressive weight loss, vomiting and soft faeces. Serum cobalamin is low. Ultrasound shows diffuse thickening of the muscularis layer of the jejunum and ileum with mildly enlarged mesenteric lymph nodes. Gastroduodenoscopy, without colonoscopy, reports moderate lymphoplasmacytic enteritis in the duodenum.
What is the most appropriate course of action?
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A. Obtain ileal or full-thickness biopsies with immunohistochemistry
Correct. Feline small cell lymphoma frequently involves the jejunum and ileum, and duodenal-only biopsies may miss it. Ileal biopsies via colonoscopy, or full-thickness biopsies via surgery or laparoscopy, with immunohistochemistry and, if doubt persists, clonality testing, greatly increase diagnostic yield.
B. Treat as inflammatory enteropathy with prednisolone and diet
Duodenal biopsies do not represent the thickened jejunum and ileum. Treating as inflammatory enteropathy may delay the diagnosis of lymphoma, which has a different treatment (chlorambucil) and prognosis.
C. FNA cytology of the thickened muscularis to confirm lymphoma
Cytology cannot reliably distinguish small cell lymphoma from lymphocytic inflammation, because both show small, well-differentiated lymphocytes.
D. Clonality PCR on the duodenal biopsy as the definitive test
Clonality testing is complementary: it gives false positives (pseudoclonality) in inflammation and false negatives, and must be interpreted with histology and immunohistochemistry of the affected segment, which has not been biopsied here.
lightbulb Key takeaway
In a cat with small intestinal muscularis thickening, the jejunum and ileum are the target. If you perform endoscopy, add colonoscopy to biopsy the ileum; histology with immunohistochemistry is the cornerstone, and clonality only complements it.
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Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.