Feline chronic enteropathy (FCE) is common, especially in senior cats (Marsilio, 2021), and it can be diagnostically challenging. Clinical signs are often subtle, slowly progressive and non-specific, and many cats are not presented until weight loss, appetite change or recurrent vomiting has been present for some time. Even then, distinguishing inflammatory disease from other important differentials, especially low-grade alimentary lymphoma, is not always straightforward. A structured but pragmatic diagnostic approach is therefore essential.
Terminology used in feline chronic GI disease continues to evolve. In line with Riggers et al. (2023), this article uses:
FCE is best viewed as a clinical umbrella rather than a single diagnosis. It includes feline chronic inflammatory enteropathy (FCIE) as well as important differentials that can closely mimic it, particularly low-grade alimentary lymphoma.
Diagnosis of FCE can be challenging for several reasons:
The starting point in the diagnostic pathway is a careful history and clinical examination. This should establish the duration and progression of signs, appetite and weight trends, vomiting frequency, faecal quality, any previous diet trials, prior medications and treatment response, and evidence of extra-gastrointestinal disease. It may also be useful to establish how far the owner is willing to go with investigation, hospitalisation or invasive sampling, because this often shapes the route the work-up takes in practice.
Cats with FCE may present with:
And less commonly:
A diagnosis of FCE, and more specifically FCIE, requires a structured work-up aimed at excluding other causes of chronic GI disease while assessing for intestinal inflammation and important differentials such as lymphoma. In practice, no single test is diagnostic, and interpretation depends on the pattern of findings across the work-up.
Initial investigation typically includes faecal testing, haematology, serum biochemistry and abdominal imaging, with additional GI-specific tests used where indicated.
Radiography is generally non-specific in FCE and is often less informative than ultrasonography.
Abdominal ultrasonography may reveal changes such as diffuse thickening of the intestinal wall or muscularis layer, altered mucosal appearance and mesenteric lymphadenopathy. However, these findings are neither sensitive nor specific for FCIE, and ultrasonographic appearance may be normal even in affected cats (Guttin, et al., 2019; Daniaux, et al. 2014). Ultrasonographic findings should therefore be interpreted as part of the wider diagnostic picture rather than as a stand-alone discriminator.
At this stage in the diagnostic process, clinicians often need to decide whether to proceed to more invasive investigations, begin a diet or treatment trial, or gather additional information using adjunctive tests such as faecal calprotectin to guide the next step.
In a clinically stable patient, a diet or treatment trial may be considered before endoscopy or surgical biopsy, particularly if the owner is hesitant about invasive investigation.
A response to a diet or treatment trial may be seen within two to four weeks, although this varies between individuals and it is sometimes necessary to persevere for longer. Moreover, identifying the most suitable diet for an individual patient can involve trial and error and the best solution may not be found on the first attempt.
The challenge with this approach is therefore that clinical improvement can be slow, partial or difficult to interpret. Signs may fluctuate, owners may lose confidence and the clinician may be unsure whether intestinal inflammation is improving but clinical signs are lagging behind, or whether a revised treatment plan is needed.
Faecal calprotectin is a non-invasive marker of intestinal inflammation that may provide useful additional information. It may be most helpful where the degree of underlying inflammation is unclear, where biopsy is declined or deferred, or where support is needed for decision-making around diet or treatment trials.
Reported diagnostic performance in cats with chronic enteropathy is good, with specificity of 100 percent and sensitivity of 92 percent at a threshold of 2.5 mg/kg (Carus Animal Health, 2025). However, results should always be interpreted alongside history, clinical examination and other diagnostic findings. Elevated results:
Conversely, falling concentrations on repeat testing may suggest improvement during a treatment or diet trial.
Differentiating inflammatory disease from low-grade alimentary lymphoma is a key consideration in cats with chronic GI signs. Intestinal lymphoma is broadly categorised into small-cell and large-cell forms. Large-cell lymphoma typically presents with rapidly progressive signs over days to weeks and carries a poorer prognosis, whereas small-cell lymphoma often follows a more indolent course that can closely mirror immunosuppressant-responsive enteropathy (IRE), a subset of FCIE.
Histopathology is key, but does not always provide a definitive answer. Debate continues as to whether strict differentiation between small-cell lymphoma and IRE is always necessary, with some clinicians suggesting that prognosis and treatment may overlap (Marsilio, 2021). When required, immunohistochemistry for immunophenotyping and PCR testing for B- and T-cell clonality can help clarify the diagnosis (Kiupel, M. et al., 2011).
Histopathology remains the gold standard for the definitive diagnosis of FCIE and for distinguishing inflammatory disease from important differentials, including alimentary lymphoma. Intestinal biopsy samples may be obtained endoscopically, allowing collection of mucosal biopsies from accessible regions of the GI tract, or surgically, where full-thickness samples are required or considered more appropriate.
As well as helping to rule out important differentials, histopathology allows inflammatory disease to be characterised by cell type. In cats, inflammation is most commonly lymphocytic-plasmacytic, sometimes with an eosinophilic component (Washabau, et al., 2010).
Histopathology is particularly important where:
That said, many cats are managed without histological confirmation because of cost, anaesthetic concerns or owner preference. In those cases, clinicians often have to work with a presumptive diagnosis and a staged plan, using available evidence to support the most appropriate next step.