Pathology Cheat Sheet
Read the Tissue Reaction
Infection reaction patterns for NEET-PG: suppurative, necrotising, granulomatous and viral cytopathic change, special stains, and host-determined lesions.
MedNext Academy | 3 min read
Read the Tissue Reaction
Infection reaction patterns for NEET-PG: suppurative, necrotising, granulomatous and viral cytopathic change, special stains, and host-determined lesions.
The limited set of tissue reaction patterns by which pathologists recognise infection across bacterial, viral, protozoal and helminthic disease.
High-yield lines
- The host immune status shapes the lesion pattern as much as the organism itself does.
- Suppurative inflammation with neutrophils and pus is typical of pyogenic bacteria such as staphylococci and streptococci.
- Necrotising infection is dominated by tissue death, as in clostridial gas gangrene and necrotising fasciitis.
- Granulomatous inflammation walls off intracellular organisms such as mycobacteria and fungi with epithelioid macrophages.
- Viral infection produces cytopathic changes including inclusion bodies and multinucleate giant cells.
- Parasitic tissue reactions often show eosinophil-rich infiltrates around larvae or cysts.
- Ziehl-Neelsen stain demonstrates acid-fast mycobacteria as red bacilli on a blue background.
- Giemsa stain highlights intracellular parasites such as malarial rings and Leishmania amastigotes.
- Periodic acid-Schiff and Gomori methenamine silver stains highlight fungi in tissue.
- Immune injury rather than direct cytopathicity causes most hepatocyte damage in viral hepatitis B.
- Anergic or non-reactive infection in immunosuppression shows many organisms with little inflammation.
- The portal of entry predicts the expected lesion, as inhalation causes pulmonary disease and feco-oral entry causes intestinal disease.
Mapped competency codes
- PA10.4
Continue into the full chapter
This summary maps to PA10-infections-and-infestations.
Frequently Asked Questions
What are the main tissue reaction patterns of infection?
Suppurative inflammation, necrotising infection, pseudomembranous inflammation, granulomatous inflammation, viral cytopathic change, and parasitic tissue reaction.
Why does the same organism cause different lesions in different patients?
Because host immune status shapes the response, so an immunocompetent patient may form organised granulomas while an immunosuppressed patient shows many organisms with little inflammation.
Which stain identifies acid-fast bacilli?
The Ziehl-Neelsen stain, which shows mycobacteria as red bacilli against a blue counterstained background.
What reaction pattern indicates a viral infection?
Cytopathic change with viral inclusion bodies, multinucleation, and a mononuclear inflammatory infiltrate.
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