Pneumocystis Carinii Pneumonia (PCP)

Pathophysiology:  Pneumocystis carinii is a ubiquitous organism.  It is not pathologic in the normal host but is pathologic in immunocompromised hosts especially those with HIV.  It is not a community acquired pneumonia (CAP) and is not spread from host to host.  An inflammatory process begins in interalveolar walls with desquamation of alveolar cells leading to diffuse alveolar damage and varying degrees of inflammatory reaction.

Clues:

1.     The CXR presentation has changed over the years. At the beginning of the HIV epidemic, PCP patients often presented in acute respiratory failure with an ARDS lung pattern.

2.      PCP often presents with co-existing pneumonias and superinfections.

3.      Commonest pneumonia in HIV patients is still CAP.

CXR Findings:

1.      Classic: peri and infra hilar interstitial changes which coalesce

2.      Infrahilar inverted triangle-like densities from the hila to the lung bases

3.      Many variations: diffuse airspace changes, rarely nodular areas, rarely cavitary areas

4.      Pleural reactions NOT marked; small effusions may be seen

5.      NOT associated with significant adenopathy on plain films

6.      Definite association with pneumothoraces

Complications/Associations in HIV patients:

1.      Non T-cell Lymphoma

2.      Kaposi's sarcoma with lung metastases

3.      Tuberculosis and atypical tuberculosis especially MAI

4.      Pneumothoraces

“Aunt Sophies”: (with appropriate history, easy to diagnose in its typical form)

1.      Pulmonary edema or ARDS pattern

2.      CAP

3.      Tuberculosis (typical and atypical)