Inflammatory Cytology and Neutrophilic Reactions

Study Notes

Neutrophilic/eosinophilic Inflammatory Reactions: These reactions are characterized by a predominance of neutrophils or eosinophils (over 80% of inflammatory cells).
Mixed Inflammatory Reactions: These reactions have approximately equal numbers of neutrophils and mononuclear cells (50% to 80% polymorphonuclear, the remaining cells mononuclear).
Macrophagic (non-suppurative, histiocytic) Inflammatory Reactions: These reactions have over 50% mononuclear cells.
Subclassification: Inflammatory reactions can be further subclassified based on the morphology of different cell lines. This provides information about the pathogenesis of the reaction and helps identify the etiology.

Two Subtypes:
- Neutrophilic with nondegenerate neutrophils: Neutrophils are morphologically similar to those in peripheral blood or have nuclear hypersegmentation.
- Neutrophilic inflammation with degenerate neutrophils: Neutrophils exhibit characteristic nuclear and cytoplasmic changes.
Nuclear Changes in Degenerate Neutrophils:
- Hyalinization and swelling of nuclei: Early stage of karyolysis.
- Pyknosis: Intensely stained nuclei.
- Karyorrhexis: Pyknotic nuclei fragmented into small pieces.
- Karyolysis: Dissolution of the nucleus with nuclear chromatin streaming away from the nucleus into the cytoplasm.
Cytoplasmic Changes in Degenerate Neutrophils: Homogeneous, glassy, and slightly basophilic cytoplasm.
Neutrophilic Inflammation with Nondegenerate Neutrophils: Indicates severe irritation. The etiologic agents are often not observed.
Neutrophilic Inflammation with Degenerate Neutrophils: Indicates severe irritation and destruction of neutrophils.
Significance of Nuclear Hyalinization, Swelling, and Karyolysis: Indicate acute cell death in neutrophils, often due to local toxins, such as bacterial toxins. Karyolysis suggests sepsis, even if bacteria are not observed.

Neutrophil Morphology: Can be used to subclassify these reactions, similar to the neutrophilic inflammation.
Macrophage Morphology:
- Typical macrophages: Large, round to oval cells (20–35 µm) with eccentric round or irregular nuclei.
- Nuclei: Lacy or reticulate chromatin pattern.
- Cytoplasm: Abundant, granular, and faintly eosinophilic.
- Cytoplasmic Vacuoles: Contain phagocytized material (cellular debris, RBCs, or specific etiologic agents).
Epithelioid Cells:
- Morphology: Morphologically similar to macrophages, but cytoplasm contains fewer or smaller vacuoles and lacks phagocytized material.
Inflammatory Giant Cells:
- Morphology: Large, multinucleated macrophages. May contain phagocytized material or have epithelioid cell-like cytoplasm.
Subclassification of Mixed or Macrophagic Reactions:
- Pyogranulomatous: Contains both neutrophils and granulomatous components.
- Granulomatous: Predominantly contains epithelioid or giant cells.

Etiology: Suggests less severe irritation than neutrophilic reactions, often associated with resolving neutrophilic inflammation.
Significance: Indicate a longer-lasting and more complex inflammatory process, often involving immune responses and chronic inflammatory conditions.