I have a 10-year-old spayed female DSH cat with a two-mon...

This sounds like a very classic presentation for feline gastrointestinal lymphoma, and your suspicion is certainly warranted, especially with the diffuse jejunal thickening and previous non-diagnostic FNAs. It’s incredibly frustrating when cytology doesn't give us the answers we need, but for feline GI lymphoma, particularly the small cell variant, this is a common hurdle. Differentiating high-grade IBD from low-grade lymphoma can be a diagnostic tightrope.

Here are my recommendations for moving forward:

1. Definitive Diagnosis: The Crucial Next Step

Given the non-diagnostic FNAs and the diffuse nature of the thickening, we absolutely need a definitive diagnosis to guide our treatment. The key is to obtain full-thickness biopsies of the affected bowel.

* Surgical Biopsy (Preferred for Definitive Dx): This is often the gold standard for GI lymphoma, especially when diffuse disease or deeper layers are suspected. A laparotomy allows for full visualization, palpation, and the collection of multiple full-thickness biopsies from different affected segments (e.g., jejunum, ileum). This method provides the most comprehensive tissue architecture for the pathologist.
* Endoscopic Biopsy (Less Invasive, but with Limitations): While less invasive, endoscopic biopsies are often superficial. In cases of diffuse jejunal thickening, it can be challenging to get enough depth to differentiate lymphoma from severe inflammatory infiltrates, or to capture the full extent of the neoplastic cells. If endoscopy is pursued, ensure multiple samples (at least 6-8) are taken from various sites and depths within the abnormal areas.

Regardless of the biopsy method, it is critical to submit samples for:

* Histopathology: This will provide the definitive diagnosis of lymphoma and, most importantly, allow for grading (small cell/lymphocytic vs. large cell/high grade). The grade dictates our entire treatment approach and prognosis.
* Immunohistochemistry (IHC): This is essential for immunophenotyping (T-cell vs. B-cell). While less prognostic in feline GI lymphoma compared to canine multicentric lymphoma, it can still provide useful information.
* PCR for Antigen Receptor Rearrangements (PARR): This molecular test can be invaluable for differentiating clonality. If histopathology is equivocal (e.g., severe lymphoplasmacytic enteritis vs. small cell lymphoma), a positive PARR result strongly supports lymphoma.

Why the emphasis on grading? The prognosis and treatment for small cell vs. large cell feline GI lymphoma are vastly different.

2. Initial Chemotherapy Protocol: Tailored to Grade

Your mention of prednisolone and chlorambucil is spot on for small cell (lymphocytic) feline GI lymphoma. If the biopsies confirm this diagnosis, it's an excellent first-line protocol.

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A. For Small Cell (Lymphocytic) GI Lymphoma:

This is a highly effective and generally well-tolerated oral protocol.

* Prednisolone: Start with 2 mg/kg PO daily. In cats, prednisolone is preferred over prednisone due to variable hepatic conversion. We typically maintain this dose for 2-4 weeks, then begin a gradual taper over several months as the patient responds.
* Chlorambucil: 2 mg/cat PO daily. This can be given long-term.
* Monitoring: With this protocol, we'll monitor CBCs every 2-3 weeks initially to assess for myelosuppression (primarily neutropenia), especially with chlorambucil. Clinical response (cessation of vomiting, weight gain, improved appetite, resolution of hypoalbuminemia) is also critical.

* Prognosis: With this regimen, many cats achieve long-term remission, with median survival times often ranging from 2 to 3 years, and some living significantly longer. Quality of life is typically excellent.

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B. For Large Cell (High Grade) GI Lymphoma:

If the biopsies reveal large cell lymphoma, the prognosis is unfortunately much guarded, and a more aggressive multi-agent IV chemotherapy protocol is indicated.

* COP or Modified CHOP Protocol: These protocols typically involve:
* Vincristine: 0.5-0.7 mg/m² IV weekly (per protocol).
* Cyclophosphamide: 200-250 mg/m² PO or IV every 3 weeks. Always administer with furosemide to prevent sterile hemorrhagic cystitis.
* Doxorubicin: 1 mg/kg (max 25 mg/m²) IV slow infusion every 3 weeks. Cats are more prone to nephrotoxicity with doxorubicin than cardiotoxicity, so renal values must be closely monitored.
* Prednisolone: 2 mg/kg PO daily (tapering as part of the protocol).
* Prognosis: For large cell lymphoma, even with aggressive multi-agent chemotherapy, median survival times are typically much shorter, often ranging from 4 to 9 months.

3. Staging and Adjunctive Care

Before initiating any chemotherapy, ensure complete staging:

* FeLV/FIV Status: Essential for all feline lymphoma cases.
* Thoracic Radiographs (3 views): To rule out mediastinal or pulmonary involvement.
* Abdominal Ultrasound: Re-evaluate for other sites of disease (e.g., mesenteric lymph nodes, liver, spleen).
* Bone Marrow Aspirate: Consider if severe cytopenias are present, though less common for primary GI lymphoma.
* Supportive Care: Address the anemia and hypoalbuminemia as needed. Nutritional support (e.g., appetite stimulants like mirtazapine 1.88 mg/cat PO q48h, or a feeding tube if anorexia is severe) will be crucial. Cobalamin supplementation is almost always indicated in cats with chronic GI disease.

In Summary

The most critical step now is obtaining a definitive, graded diagnosis via full-thickness surgical biopsies (or comprehensive endoscopic biopsies with PARR). Once we know the specific type of lymphoma, we can confidently choose the most appropriate and effective chemotherapy protocol. For small cell lymphoma, prednisolone and chlorambucil offer an excellent prognosis and quality of life. For large cell, we'll need to discuss a more aggressive, but unfortunately less curative, approach with the owners.

Please keep me updated once you have the histopathology results. We can then fine-tune the treatment plan together.