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Pulmonary Pathology Online

Role of Cytopathology in the Diagnosis of Opportunistic Infections

Dr Sampurna Roy MD 




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.

Visit: Infectious Disease Online

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.

Other fungi:

Aspergillus and Candida species cause opportunistic infections, but both occur more commonly in respiratory specimens as aerial and oropharyngeal contaminants respectively.

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.

Viral infection: 

Cytomegalovirus and Herpes Simplex Virus are the two opportunistic viral infections most commonly encountered.

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:

Bacterial infections such as Mycobacterium Tuberculosis and Atypical Mycobacteria, Nocardia and Actinomyces species may be detected by Ziehl Neelsen.

Grocott and Gram stains respectively but require microbiological confirmation.

Protozoal and parasitic infections are also encountered in immunocompromised patients.  


Further reading:

Phaeohyphomycosis fungal infections in solid organ transplant recipients: clinical presentation, pathology, and treatment.

Cytomegalovirus disease in patients with common variable immunodeficiency: three case reports.

Neurologic complications of HIV infection: highlights from the 2013 Conference on Retroviruses and Opportunistic Infections.

The utility of cytopathology testing in lung transplant recipients.

Disseminated nocardiosis diagnosed by fine needle aspiration biopsy: quick and accurate diagnostic approach.  

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. 

Pneumocystis carinii pneumonia in HIV-infected patients: diagnostic yield of induced sputum and immunofluorescent stain with monoclonal antibodies.  

Upper and middle lobe bronchoalveolar lavage to diagnose Pneumocystis carinii pneumonia.

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.

Pulmonary aspergillosis and the importance of oxalate crystal recognition in cytology specimens.



Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)






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