Page 51 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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6.3 Eosinophilic Inflammation
VetBooks.ir General information

• Eosinophils regulate acute hypersensitivity reactions (type I hypersensitivity) and are typic-
ally present in allergen- and parasite-mediated inflammatory reactions.
Cytological features

• Eosinophilic inflammation is diagnosed when the sample contains significant numbers of
eosinophils (by convention > 10%).
• Eosinophils are polymorphonuclear leucocytes with lobulated nuclei.
• Canine eosinophils contain round orange to pink granules, which may significantly
vary in size and colour.
• Feline eosinophils contain numerous small rod-shaped granules with more delicate
staining properties than in dogs.
• In eosinophilic plaque/granuloma lesions, there is a prevalence of eosinophils, especially in
the feline species. Small numbers of granulated mast cells, small lymphocytes, macrophages
and neutrophils are also commonly observed. Reactive fibroblasts and amorphous baso-
philic material may be present as a result of collagenolysis.
• In most of the eosinophilic inflammations caused by hypersensitivity, such as insect/flea-bite
reaction, inflammatory cells are often mixed. Eosinophils, small lymphocytes, granulated
mast cells, neutrophils and macrophages are present in variable proportions.

Causes
• Insect-bite reaction.
• Eosinophilic granuloma complex (EGC).
• Immune-mediated process.
• Parasitic or fungal infection.
• Paraneoplastic inflammation (e.g. mast cell tumour, T-cell lymphoma).

Pearls and Pitfalls
Charcot-Leyden crystals are large eosinophilic structures that result from the coalescence of
eosinophil granules into large crystals. They can occur in any condition that causes eosinophils
to accumulate.