Pulmonary Pathology Online
Role of Cytopathology in the Diagnosis of Opportunistic Infections
The respiratory tract is a common site for opportunistic infections whether immunosuppression is iatrogenic or secondary to an immunosuppressive disease.
Cytological sampling is a rapid , accurate, minimally invasive method of achieving a diagnosis prior to confirmation by microbiological techniques.
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Pneumocystis carinii :
- Previously classified as protozoal, now identified as a fungal infection.
- Usually diagnosed in bronchoalveolar lavage samples but can be seen in sputum, induced sputum and even in saliva.
- Plaques of amphophilic alveolar exudates are present with a fine honeycomb structure representing cyst spaces.
- Usually present in a clean background with few inflammatory cells.
- Grocott methenamine silver staining is optimal for demonstrating the cyst walls, with one or two central stained bodies.
- Empty cysts are crescent shaped and are frequent in long standing or partially treated cases.
- Trophozoites may be identified with Giemsa stain.
- Immunoflourescence, DNA hybridization and PCR are more sensitive than routine cytology.
- Papanicolaou stained samples should be fully screened for evidence of other opportunistic infections, particularly cytomegalovirus and herpes simplex virus.
- Look-alikes include the amorphous plaques of amphophilic material seen in pulmonary alveolar proteinosis and amyloidosis.
- Red blood cells, other fungi, bacteria and artifacts may take up silver stains.
Absence of inflammatory cells and the background salivary setting, with evidence of fungal and bacterial overgrowth usually enables a distinction between genuine infection and contamination to be made.
The owl’s eye inclusions of Cytomegalovirus and the multinucleation with a ground glass chromatin pattern in moulded nuclei caused by Herpes Simplex Virus are characteristic.
Immunostaining can be performed for confirmation.
To the inexperienced eye, herpetic changes may be mistaken for malignancy.
Other opportunistic Infections:
Grocott and Gram stains respectively but require microbiological confirmation.
Protozoal and parasitic infections are also encountered in immunocompromised patients.
Diagnosis of Pneumocystis carinii pneumonia by multiple lobe, site-directed bronchoalveolar lavage with immunofluorescent monoclonal antibody staining in human immunodeficiency virus-infected patients receiving aerosolized pentamidine chemoprophylaxis.
Blinded comparison of a direct immunofluorescent monoclonal antibody staining method and a Giemsa staining method for identification of Pneumocystis carinii in induced sputum and bronchoalveolar lavage specimens of patients infected with human immunodeficiency virus.
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