Impression cytology in cats: degenerate neutrophils and cocci
4-year-old domestic shorthair cat with intense facial pruritus and exudative erosions on the face and neck. The crust is lifted and a direct impression is taken with a glass slide, stained with Diff-Quik: many degenerate neutrophils with intracytoplasmic cocci, some eosinophils and free cocci.
How do you interpret this cytology?
chevron_right Show answer and explanation
A. Active bacterial infection, probably secondary to an underlying pruritic disease
Correct. Phagocytosis of bacteria by degenerate neutrophils proves true infection, not mere colonisation. In cats, infection usually complicates feline atopic skin syndrome, food allergy or ectoparasites: treat both the infection and the cause of the pruritus.
B. Bacterial colonisation of no clinical importance, because cocci are part of the normal flora
A few free cocci on keratinocytes may be colonisation, but cocci inside neutrophils indicate that the immune system is responding to an infection.
C. Malassezia dermatitis
Malassezia appears as oval or footprint-shaped yeasts (3–8 µm), much larger than cocci (≈1 µm), and is rarely phagocytosed by neutrophils.
D. Cutaneous mast cell tumour, because of the eosinophils
Eosinophils are common in allergic lesions and the feline eosinophilic granuloma complex. Suspecting a mast cell tumour would require mast cells with metachromatic granules.
lightbulb Key takeaway
In skin cytology, the finding that confirms bacterial infection is bacteria phagocytosed by degenerate neutrophils. Direct impression suits moist lesions or those under crusts; acetate tape suits dry and greasy skin.
Test yourself with 10 random questions
Dermatology · 100 questions, a different test every time
Related questions
Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.