Extreme thrombocytosis in a young cat

Area of Science:

• Veterinary Medicine
• Infectious Diseases
• Hematology

Background:

• A 7-month-old domestic shorthair cat presented with inappetence, hypersalivation, fever, gingivitis, and oral ulceration.
• Initial diagnostics revealed leukopenia, neutropenia, and elevated titers for feline panleukopenia virus (FPV) and feline calicivirus (FCV), suggesting a coinfection.

Purpose of the Study:

• To investigate the cause of severe, persistent thrombocytosis in a young cat coinfected with FPV and FCV.
• To explore potential differential diagnoses, including reactive thrombocytosis and essential thrombocythemia, for the observed extreme platelet count.

Main Methods:

• Clinical examination and serological testing for FPV and FCV.
• Complete blood count (CBC) and blood smear examination to assess platelet levels.
• Monitoring of platelet count over time (day 10 and day 35 post-initial presentation).

Main Results:

• The cat exhibited severe leukopenia and neutropenia, consistent with FPV and FCV coinfection.
• A marked thrombocytosis was observed, with platelet counts reaching 3,448 × 10^9/L (day 10) and 4,990 × 10^9/L (day 35), significantly exceeding the reference range.
• The extreme and persistent thrombocytosis prompted consideration of reactive causes versus essential thrombocythemia, a diagnosis of exclusion.

Conclusions:

• The case presents an unprecedented level of persistent thrombocytosis in a feline coinfection scenario without a confirmed neoplastic process.
• While infection can cause reactive thrombocytosis, the magnitude and duration in this case warrant further investigation into underlying pathophysiology.
• This case underscores the importance of considering extreme hematological responses in feline infectious diseases and the diagnostic challenges they present.