Page 54 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Inflammatory Lesions
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6.4 Lymphocytic Inflammation
VetBooks.ir General information

• Lymphocytes participate in both the humoral and cell-mediated adaptive immune
response. They are also involved in type IV (delayed) hypersensitivity reactions.
• They are commonly seen in established or chronic inflammatory processes.

Cytological features
• Lymphocytic inflammation is diagnosed when the sample contains a vast majority of
lymphocytes.
• This type of inflammation is often characterized by a mixed population of lymphoid cells,
predominantly small lymphocytes. Low numbers of intermediate and/or large lymphoid
cells may also be noted.
• Macrophages and plasma cells can also accompany small lymphocytes in chronic inflamma-
tory processes. When significant numbers of plasma cells are present, the term lymphoplas-
macytic inflammation can be used instead.

Causes
• Non-specific chronic inflammation.
• Vaccine reaction.
• Regressing histiocytoma.
• Insect-bite reaction.
• Viral infection.

Differential diagnoses
• Cutaneous lymphoma
• Regressing histiocytoma (late stages)

Pearls and Pitfalls
• Reactive lymphoid follicles may form in the dermis in association with chronic inflamma-
tion/stimulation. Aspiration can yield a mixed population of lymphoid cells and lym-
phoglandular bodies (cytoplasmic fragments).
• In the presence of a main population of small lymphocytes, differentiation between
lymphocytic inflammation and small cell lymphoma may not be possible on cytology
alone, and it may require additional tests for definitive diagnosis. These include histo-
pathology, immunophenotyping techniques, and/or clonality testing (PARR). When
intermediate and/or large lymphoid cells prevail, the diagnosis of (cutaneous) lymphoma
is straightforward.