Page 44 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

VetBooks.ir 6 Inflammatory Lesions

Inflammation is classified on cytology based on the predominant cell type involved. It is
subdivided into the following categories:
• Neutrophilic
• Macrophagic
• Eosinophilic
• Lymphocytic
• Mixed (in the absence of a prevalent cell type)

The recognition of the inflammatory pattern helps the pathologist to restrict the list of differential
diagnoses and sometimes also to identify a potential aetiology. Inflammation can be sterile or
associated with an infectious disease. However, the absence of microorganisms on cytology does
not rule out an infectious cause, and further testing with a higher sensitivity (e.g. bacterial cul-
ture, polymerase chain reaction (PCR)) may be required.
Inflammation may be the sole pathologic process causing the formation of the cutaneous
lesion or it may be associated with hyperplastic, dysplastic and neoplastic processes.
The algorithm in Fig. 6.1 shows a correct approach to cutaneous inflammatory lesions.

NO
Sterile irritants
Immune-mediated disease
Neoplasia
Mostly neutrophils Are they Occasionally, bacterial
(neutrophilic degenerate? infection
inflammation)
YES
Bacterial infection
Necrosis
In vitro swelling (fluids)
Macrophages with or Foreign body
without neutrophils
INFLAMMATORY (macrophagic or Fungal infection
CELLS pyogranulomatous Mycobacteriosis
Chronic stimulus/inflammation
inflammation)
> 10% eosinophils Hypersensitivity/allergic disorder
(eosinophilic Parasitic disease
inflammation) Paraneoplastic (e.g. MCT, T-cell lymphoma)

Lymphocytes and
plasma cells Allergy, immune stimulation
(lymphocytic/ Early viral infection
lymphoplasmacytic Chronic inflammation
inflammation)
Fig. 6.1. Schematic approach to the cytology of inflammatory lesions.

© Francesco Cian and Paola Monti 2019. Differential Diagnosis in Small Animal Cytology 31
(F. Cian and P. Monti)