Young cat with serious problems


Antonio Meléndez-Lazo DVM, MSc, PhD, DipECVCP, MRCVS - LABOKLIN

SIGNALMENT AND HISTORY
A 1-year-old, Devon Rex neutered male cat was presented to the veterinary due to hyporexia, apathy and “swollen belly”. The cat was adopted one month earlier from a breeder and his FeLV/FIV status was negative according to the information given by the breeder. The cat was doing well previously, and the owners did not observe any abnormal behaviour or clinical sign.

PHYSICAL EXAMINATION:
On general physical examination, the cat presented a good body condition score of 4/9 and abdominal distention. Abdominal palpation showed a moderate amount of free fluid, with positive wave test.   Hyperthermia was also present (39.9ºC) but no other abnormalities were found.

INVESTIGATION
Haematology and biochemistry
Complete blood count and serum biochemistry profile were done as part of routine diagnostic workup. Hematology results revealed a mild normocytic, normochromic, nonregenerative anemia and mild leukocytosis with mature neutrophilia and lymphopenia. Blood smear examination was unremarkable.

Biochemistry and serum protein electrophoresis revealed mild hypoalbuminemia (29 g/dL, reference interval 30-45), and hyperglobulinemia (42 g/L, reference interval 4-19) and mild increased in total bilirubin concentration (Figure 1).

Figure 1. Capillary zona electrophoresis electrophoretogram with marked hyperglobulinemia.

Diagnostic imaging
Abdominal ultrasound examination revealed a moderate amount of free fluid and mildly reactive peritoneum, with no other abnormalities found.

The fluid obtained by ultrasound-guided abdominocentesis is represented in Figure 2.

Figure 2. Macroscopic appearance of abdominal fluid.

What is your interpretation of the haematology and biochemistry?
What is the main differential diagnosis in this case based on the signalment and clinical findings in this case?
What further tests could you do to confirm your presumptive diagnosis?


What is your interpretation of the haematology and biochemistry?
Mild normocytic normochromic and nonregenerative anaemia likely reflects anaemia of chronic inflammation. Mild neutrophilia and lymphopenia probably reflect a response to endogenous o exogenous steroids (stress leukogram), although mild inflammation is also possible.
Increased globulins concentration also indicates inflammation, a serum protein electrophoresis would help to better characterize the type of hyperproteinemia. The clinical significance of the mild increased in total bilirubin concentration is uncertain, as there is no evidence for hemolysis, increased liver enzyme activities or hepatic cholestasis.

What is the main differential diagnosis in this case based on the signalment and clinical findings in this case?
Given the age and the clinical signs, effusive (“wet”) form of feline infectious peritonitis is the most likely diagnosis. Other possible but unlikely diagnoses may include other infectious diseases, pancreatitis, liver lobe torsion.

What further tests could you do to confirm your presumptive diagnosis?
Fluid analysis including total nucleated cell count and total proteins, cytology, Rivalta test and Feline Coronavirus PCR (FCoV).

-    Fluid analysis
•    TNCC: 3450 cells/microliter
•    Total proteins (refractometry): 45 g/L
•    Cytology: there was a predominance of poorly preserved neutrophils with low number of foamy macrophages and rare reactive mesothelial cells. The background was pinkish and granular, indicating a high protein content (Figure 3).

 

Figure 3. Abdominal fluid cytology. Poorly preserved neutrophils in a proteinaceous background (Modified Wrigth staining, 40x).

•    Rivalta test: POSITIVE (Figure 4).
To perform Rivalta test, 8ml of distilled water were mixed with one drop of acetic acid (white vinegar can also be used). One drop of the effusion is carefully placed on the surface of the solution and, if the drop retains its shape in the fluid or forms a jellyfish-like shape, then the test is positive. If the drop of the effusion disappears, the test is negative.

Figure 4. Positive Rivalta test. Note the drop of effusion attached to the surface of the solution.

•    FCoV real time PCR: POSITIVE

DIAGNOSIS: Consistent with effusive form of Feline Infectious Peritonitis

FOLLOW UP
In the presented case, the owners decided because of the poor general condition of the cat against therapy and for euthanasia.

Of course it is not our opinion that this procedure should be recommended in general! The current recommendations for therapy are complex – therefore we refer to the EUROPEAN ADVISORY BOARD ON CAT DISEASES. All currently recommended procedures are listed there:
http://www.abcdcatsvets.org/feline-infectious-peritonitis/
Studies on newer antiviral drugs are ongoing, some reports exist (JVIM, Dickinson et al. on GS-441524), but these drugs are still not approved.

SUMMARY
Feline Infectious Peritonitis (FIP) is a worldwide distributed infectious disease caused by Feline Coronavirus (FCoV).

Predisposing factors include pure breed and an age under 2 years old. Some authors have noted increased prevalence in male over female cats, while others found no sex predisposition.
The main route of FCoV transmission is fecal-oral, especially at young age in breeding catteries with high animal density. Host immune response is a key factor for the development of disease, either effusive (with mainly humoral response and vasculitis) or non-effusive (with mainly cellular response and granulomatous lesions formation) but also virulent factor of the virus are determinant for the development of disease.
FCoV viraemia when it occurs, is short, peaking about 7 days post-infection and declining thereafter. Antibody production to FCoV takes 10-28 days post-infection.
Clinical signs may vary widely between the effusive and non-effusive forms depending on the distribution of vasculitis and granulomatous lesions and may also vary over time. Non-specific clinical signs include lethargy, anorexia, wight loss, increased size of abdominal lymph nodes and fever. Cavitary effusions, neurological, ophthalmological and dermatological symptoms are also possible.
In effusive forms, analysis of the effusion can aid on the diagnosis of FIP. FIP related effusions are usually of relatively low cellularity (<5 x109/L) and high total protein concentration (>35 g/L). Macrophages and nondegenerate neutrophils are the predominant cells. Rivalta test is useful to rule out FIP when negative, but positive results are not specific for FIP.
Hematological and clinical biochemistry findings are usually unspecific and include mild to moderate nonregenerative anemia, hyperglobulinemia and hypoalbuminemia, increased total bilirubin concentration and increased acute phase proteins.
The gold standard for the diagnosis of FIP is the histopathological examination of affected tissues with compatible changes and positive immunostaining. Immunostaining of cytological smears is also possible and help in the diagnosis. However, sensitivity is variable and ranges from 57 to 100% among studies.
RT-PCR from tissue and effusion also support the diagnosis of FIP when immunohistochemistry or immunocytochemistry is not available. However, it is important to remember that cats without FIP can be positive for FCoV in tissues and fluids. Antibody tests for FCoV are generally not particularly useful.  Detection of mutations affecting FCoV spike (S) gene have shown variable results. Mutations have been found in animals infected with FCoV that do not develop FIP while sick animals with FIP have resulted negative for the mutation.

Prognosis is poor and cautions regarding contact with other cats should be taken. Treatment may include antivirals and immunomodulators together with symptomatic treatment (i.e. immune-suppressive and anti-inflammatory drugs).  

In conclusion, FIP is a complex disease and diagnosis is usually difficult, especially in effusive forms. Laboratory test results should be interpreted together with patient signalment, clinical signs and all possible information to support the diagnosis given the important consequences of a wrong diagnosis on the patient management.



References:

-    Abcdcatsvets.org/feline-infectious-peritonitis
-    Addie D, Belak S, Boucraut-Baralon C, Egberink H, Frymus T, Gruffydd-Jones T, et al (2009): Feline infectious peritonitis. ABCD guidelines on prevention and management. J Feline Med Surg 11, 594–604.
-    Addie DD, Paltrinieri S, Pedersen NC (2004): Recommendations from workshops of the second international feline coronavirus/feline infectious peritonitis symposium. J Feline Med Surg 6, 125-130
-    Barker EN, Stranieri A, Helps CR, Porter E, Davidson AD, Day MJ, Kipar A, Tasker S (2017): Limitations of using feline coronavirus spike protein gene mutations to diagnose feline infectious peritonitis. Vet Res 48, 60.
-    Fischer Y, Sauter-Louis C, Hartmann K (2012a): Diagnostic accuracy of the Rivalta test for feline infectious peritonitis. Vet Clin Pathol 41, 558-567.
-    Giori L, Giordano A, Giudice C, Grieco V, Paltrinieri S (2011): Performances of different diagnostic tests for feline infectious peritonitis in challenging clinical cases. J Small Anim Pract 52, 152-157.
-    Hartmann K, Binder C, Hirschberger J, Cole D, Reinacher M, Schroo S, Frost J, Egberink H, Lutz H, Hermanns W (2003): Comparison of different tests to diagnose feline infectious peritonitis. J Vet Int Med 17, 781-790.
-    Norris JM, Bosward KL, White JD, Baral RM, Catt MJ, Malik R (2005):   Clinicopathological findings associated with feline infectious peritonitis in Sydney, Australia: 42 cases (1990 – 2002).  Austral Vet J 83, 666-673.
-    Pedersen NC (2009): A review of feline infectious peritonitis virus infection: 1963-2008. J Feline Med Surg 11, 225-258.
-    Tasker S (2018): Diagnosis of feline infectious peritonitis: update on evidence supporting available tests. J Feline Med Surg 20, 228-243