<B>Pneumocystis Carinii Pneumonia </B>

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Pneumocystis Carinii Pneumonia

Etiology:

• Parasite found widely

Pathogenesis:

• Organism binds to type 1 alveolar pneumocytes
• Proliferates within the alveolus
• Results in intralveolar accumulation of proteinaceous material
• Mild inflammation of septae
• Resolves generally without long term scarring

Epidemiology:

• Occurs in immunocompromised patients particularly those with human immunodeficiency virus and low CD4 counts

General Gross Description:

• Focal or often diffuse
• No air on palpation, firm
• Reddish tan

General Microscopic Description:

• Bronchi are unremarkable
• Alveoli are filled with pink, foamy material
• Parasites stain with silver stains such as Gomori methinamine silver and look helmet shaped or like crushed ping-pong balls 4-6 microns in diameter
• May be congestion and mild inflammation in interstitium

Clinical Correlations:

• Present with dyspnea and dry cough
• Responds to treatment with antibiotics although difficult to eradicate in immunocompromised patients

References:
• Cotran RS, Kumar V, Robbins SL. Robbins Pathologic Basis of Disease. 5th edition. W.B. Saunders.Philadelphia 1994. p. 357.