FIP vs Lymphoma

My sweet 6yr old was in the ER on Friday in critical condition. Thankfully we were able to bring her home and she’s stable while we figure out what to do moving forward.

We have an appointment with an internist on Wednesday and I want to be as prepared as possible. Thank you in advance to anyone reading this and willing to share their thoughts! My gut (and bias for a diagnosis with hope of recovery) says mixed FIP, but lymphoma is higher on the oncologist’s list (who is extremely helpful and very open to 2nd opinions, she seriously restored my faith in attentive care).

Rescued as kitten in 2019. Lives with littermate. Indoor, access to screened 2nd floor porch, supervised in backyard on leash.

July 2024 weight = 14.4lb

April - Cough, sounded like a hairball, but not productive. OTC hairball support didn’t work.

5/13 - virtual vet visit: slightly reduced food intake, slight lethargy, RR 40 (awake); assessment - lower respiratory infection vs asthma vs endoparasites or heartworm infection vs hairball; monitor RR and recommend in person visit

5/15: Wt loss, lethargy, cough Wt = 13lb Labs: FeLV/FIV Neg CBC Hg=9.3 Hct=32.3 Plt=359k WBC=12,900 CHEM: Alb=2.7 AP=44 ALT=24 Cre=1.4 Bili=0.3N Glob=3.9

~5/27: began to notice (what we thought was) weight gain

5/30: 13.6lbs Respiratory Distress - Tx'd with O2 Removed 500 mL ascites and submitted sample to Idexx; Respiratory distress resolved, weaned off O2

5/31: 12.7lbs Labs: FeLV/FIV Neg CBC Hg=9.1 HCt= 29.7 WBC=17,920 PMN=12370 CHEM Alb=2.6 Bili=0.2 Glu=185 Glob=4.1

Thoracic Radiographs: Combined findings of hepatomegaly and the unstructured interstitial pulmonary pattern are most concerning for multicentric neoplasia such as lymphoma. Fungal disease such as histoplasmosis could be considered if there is a travel history to fungal endemic regions. Recommend correlating to liver cytology and abdominal fluid cytology. Peritoneal effusion.

Abdominal Ultrasound:

1. Hypoechoic hepatomegaly, rule out an infectious or inflammatory hepatopathy versus infiltrative neoplasia. Passive congestion is less likely given lack of hepatic venous distention and distention of the caudal vena cava.
2. Peritoneal effusion, rule out modified transudate, transudate, or neoplastic.
3. Mild duodenal and jejunal submucosal thickening, rule out enteritis, inflammatory bowel disease, or less likely small cell lymphoma.

Fluid Analysis: 4.7 g/dL 2070cells/uL This effusion has very low cellularity but a moderate to high protein concentration, consistent with a modified or protein enriched transudate. This modified transudate is predominantly lymphocytic. Lymphocyte rich transudates can be chylous or nonchylous. Fluid triglyceride concentration could be considered to further investigate the potential for a chylous effusion, but this yellow, hazy fluid does not have the stereotypical "milky" appearance of a chylous effusion. Nonchylous lymphocyte rich transudate in cats are most commonly associated with cardiovascular disease, neoplasia (lymphoma, carcinomas, etc.), and a few other uncommon causes. No overtly neoplastic cells for identified within the preparation.

Description: 3 slides are prepared from the submitted fluid. The effusion is of low cellularity and well preserved. There is a colorless to pale basophilic background with a small amount of blood. The nucleated cell population is predominated by small, well-differentiated lymphocytes. A lower number of mature, nondegenerate neutrophils and mildly vacuolated macrophages are also present. A 100 cell differential is 55% lymphocytes, 25% neutrophils, and 20% macrophages. No infectious agents or neoplastic cells are identified.

Liver Cytology: Moderate pyogranulomatous inflammation with mild hepatocellular vacuolation

Discharged 5/31/25 on Prednisolone 20mg/mL 1/2mL=10mg q 24 hours

6/2: 11.5 lb; physical exam revealed that abdominal fluid has not re-accumulated. Lost weight- possibly from her diarrhea.

Her liver aspirate suggests an infection. Her fluid analysis suggests heart disease or cancer. Zoe seems to be doing well on the prednisolone. Heart appeared normal in ultrasound.

Decreased prednisolone to 5 mg tablets - believe she has diarrhea from the high dose she is now on. Added Metronidazole Tablets, antibiotic for diarrhea.

At Home: RR 25 (asleep), increased energy, eating & drinking; she’s still a little more lethargic than usual, but other positive behaviors have resumed (running to greet at door and for her favorite brush, running to eat, sleeping on the bed, playing with her mice, grooming).

She seems to be responding very well to the steroids, which points to lymphoma, but I’ve read that can also be a short term positive response with FIP.

That’s about all I have for now. We’re so grateful she is home and feeling better, but know we’re not out of the woods yet. I would rather not delay treatment if it is FIP, but also understand why the ER vet and Oncologist didn’t weigh an FIP diagnosis as strongly.

So, vets of Reddit, what do you recommend we discuss with the internist on Wednesday? Are there enough positive indicators to begin treatment with GS-441524 while we rule out other diagnoses?

Thank you 🙏 🙏🙏