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Vetdle Archive

Archive Case #185: Feline Infectious Peritonitis

Cat veterinary case - Hard - September 4, 2026

Clinical Clues

  1. A young cat from a multi-cat environment is presented for weight loss, persistent fever, and declining energy.
  2. The cat no longer wants to play and has developed progressive abdominal distension.
  3. Examination confirms pyrexia and a fluid wave without an obvious septic focus.
  4. The abdominal effusion is straw coloured, high in protein, and relatively low in cells.
  5. A serosal biopsy shows pyogranulomatous perivascular inflammation and vasculitis.
  6. Immunohistochemistry demonstrates feline coronavirus antigen within macrophages in those lesions, confirming feline infectious peritonitis.

Diagnosis

Feline Infectious Peritonitis

This case is most consistent with Feline Infectious Peritonitis because the young cat has persistent fever and a protein-rich effusion together with pyogranulomatous vasculitis. Demonstration of feline coronavirus antigen within lesional macrophages is the decisive finding; effusion characteristics or coronavirus exposure alone would not be specific enough.

Learning review

Review the case evidence

Use the paired clues to explain how the evidence in this cat case supports the provided diagnosis, Feline Infectious Peritonitis, then compare your reasoning with the case explanation.

Evidence checkpoints

Clues 1-2

  1. Clue 1: A young cat from a multi-cat environment is presented for weight loss, persistent fever, and declining energy.
  2. Clue 2: The cat no longer wants to play and has developed progressive abdominal distension.

Clues 3-4

  1. Clue 3: Examination confirms pyrexia and a fluid wave without an obvious septic focus.
  2. Clue 4: The abdominal effusion is straw coloured, high in protein, and relatively low in cells.

Clues 5-6

  1. Clue 5: A serosal biopsy shows pyogranulomatous perivascular inflammation and vasculitis.
  2. Clue 6: Immunohistochemistry demonstrates feline coronavirus antigen within macrophages in those lesions, confirming feline infectious peritonitis.

Self-review prompts

  1. After clues 1-2, what evidence from this cat case shaped your initial interpretation?
  2. When you compare clues 3-4 with clues 1-2, what changed in your reasoning about Feline Infectious Peritonitis?
  3. How do clues 5-6 align with the case explanation for Feline Infectious Peritonitis?

Educational Use

Vetdle archive cases are educational veterinary games for diagnostic reasoning practice. They do not provide veterinary advice, diagnosis, treatment, or professional medical guidance.