Tasker S. Diagnosis of feline infectious peritonitis: Update on evidence supporting available tests. J Feline Med Surg. 2018 Mar;20(3):228-243. doi: 10.1177/1098612X18758592.
The Road to FIP Diagnosis
Often prior to the step of determining a definitive diagnosis of FIP, veterinarians will develop a disease differential list where FIP is high or first on the list of potential diagnoses. This often is due to the signalment and history of the patient, clinical signs and results of a thorough examination and routine clinicopathological test results. Experience of the practitioner in diagnosing and managing many cases of FIP can also aid in increasing the degree of suspicion of FIP. A number of disease to consider in the differential diagnosis of FIP are: toxoplasmosis, lymphocytic cholangitis, neoplasia (e.g. lymphoma, abdominal carcinoma), pancreatitis, retroviral infection, mycobacterial infection (including tuberculosis), pyothorax, sepsis, septic peritonitis, congestive heart failure, rabies (neurologic), and others.
Signalment and history: young cats (less than 3 years of age and especially less than 2 years of age) and a different smaller peak of cases in cats older than 10 years of age. Male cats seem to have a slightly higher risk and some breeds in some countries. Frequently, there is a recent history of a stressful event – adoption, shelter exposure, neutering, vaccination, other infections like upper respiratory tract disease – could be a trigger for FIP development in a cat infected with FCoV. Living in a multi-cat environment may increase FCoV seropositivity, FIP can occur in small cat households too.
Clinical signs: due to vasculopathy causing effusions (wet), or granuloma formation (dry) lesions or a combination of the two. Up to 80% of FIP cases have effusions and most cases with effusions have visible granulomatous lesions on post-mortem examination. Signs include lethargy, anorexia, weight loss, or failure to thrive. In addition, there can be a fluctuating pyrexia that is non-responsive to drugs such as antibiotics or non-steroidal anti-inflammatories along with jaundice that is more commonly noted with effusive FIP. In cats with a history of pyrexia, one study found FIP was the most common differential diagnosis. Pyrexia was more significantly found in cases with effusive FIP than those with neurological non-effusive FIP.
Lymph node enlargement can be present in both effusive and non-effusive forms. Effusions can be present in the abdomen, pleural and pericardial spaces leading to dyspnea, tachypnea and/or abdominal distension. Non-effusive disease is typically neurological (focal, multifocal, or diffuse) and/or ocular signs (uveitis). In some cases, dermatological signs (papules or nodules) can be reported in dry FIP. With kidney involvement there may be renomegaly, and pneumonia with lung involvement. Focal lymph node enlargement or gastrointestinal disease may present as palpable abdominal mass(es). Repeated examinations may be required since clinical signs of FIP can change over time and the course of the disease. Part Two (VT)
Barker EN, Helps CR, et al. Limitations of using feline coronavirus spike protein gene mutation to diagnose feline infectious peritonitis. Vet Rec. 2017 Oct 5;48(1):60.