Australian Society of CytologyCase of the Month
June 2005 - Answer and Discussion
Answer: Pneumocystis jiroveci (previously known as Pneumocystis carinii)
Cytology Findings:
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The Pap and Diff Quik stains show foamy exudates in the form of alveolar casts. The cyst walls do not stain well in these preparations but appear as clear structures within the exudates. The Diff Quik stains the trophozoites within the cysts. The Grocott's Methanamine Silver stains the cyst walls as seen above. They are cup or crescent shaped 4 to 8µm and usually occur in clusters.
Discussion
Pneumocystis jiroveci, was named in honour of a Czech parasitologist, Otto Jirovec. It was previously known as Pneumocystis carinii but this is now recognised as a separate species that does not infect humans. It was previously classified as a protozoa from its morphologic and biologic characteristics, but is currently considered a fungus based on nucleic acid and biochemical analysis.
Pneumocystis pneumonia (PCP) is an opportunistic infection that occurs in immunocompromised individuals and is now commonly associated with HIV/AIDS. Although the organism is no longer known as P carinii the disease can still use the acronym PCP which now refers to Pneumocystis Pneumonia rather than Pneumocystis Carinii Pneumonia.
Pneumocystis is an air borne pathogen and after inhalation the organisms reach the alveoli and adhere to the type 1 pneumocytes. The trophozoites then multiply slowly but extensively in the lungs and progressively fill the alveoli with foamy exudates. This exudate usually consists of clusters of Pneumocystis, degenerated cells, and a few alveolar macrophages.
A bronchoalveolar lavage sample is ideally suited to diagnose Pneumocystis. During a lavage procedure the alveoli are sampled and because Pneumocystis jiroveci is an alveolar based infection, the diagnostic sensitivity of a lavage is high.
Grocott’s methanamine silver stain is one commonly used stain to easily identify the organism. Alternatively you could use Toluidine blue or Fluorescence methods.
Treatment is an antimicrobial therapy with the drug of choice being Trimethoprim-sulfamethoxazole.
PCP may cause pneumothorax and respiratory failure which can lead to death,
especially in seriously ill patients.
References:
- De May 1999, The Art and Science of Cytopathology, ASCP Press, Chicago
- Stringer JR, Beard CB, Miller RF, Wakefield AE. A new name (Pneumocystis jiroveci) for pneumocystis from humans. Emerg Infect Dis [serial online] 2002 Sep [date cited];8. Available from: URL: http://www.cdc.gov/ncidod/EID/vol8no9/02-0096.htm
