Pneumocystosis (Pneumocystis jirovecii Pneumonia)

Key Features

Essentials of Diagnosis

• Fever, dyspnea, dry cough, hypoxia

• Often only slight lung physical findings

• Chest radiograph: diffuse interstitial disease or normal

• P jirovecii in sputum, bronchoalveolar lavage fluid, or lung tissue, PCR in bronchoalveolar lavage; (1,3)-beta-D-glucan in blood

General Considerations

• P jirovecii affects humans worldwide

• Based on serology, asymptomatic infections occur at a young age in most persons

• Overt infection is an acute interstitial plasma cell pneumonia that occurs among older children and adults who have an abnormal or altered cellular immunity, either due to

  • An underlying disease process (eg, cancer, malnutrition, stem cell or organ transplantation or, most commonly, AIDS)

  • Treatment with immunosuppressive medications, such as corticosteroids or cytotoxic agents

• Accumulating evidence suggests airborne transmission

• Pneumocystis pneumonia occurs in up to 80% of AIDS patients not receiving prophylaxis, usually at CD4 cell counts < 200/mcL

• In non-AIDS patients taking immunosuppressives, symptoms often begin when corticosteroids are tapered or discontinued

Clinical Findings

Symptoms and Signs

• Fever; tachypnea; shortness of breath; and cough, usually nonproductive

• Normal lung examination or bibasilar crackles; findings may be slight compared with degree of illness and chest radiographic abnormality

• Spontaneous pneumothorax may occur if patient had previous episodes or received aerosolized pentamidine prophylaxis

• Onset may be subacute, characterized by dyspnea on exertion and nonproductive cough

Differential Diagnosis

• Bacterial pneumonia

• Tuberculosis

• Coccidioidomycosis

• Histoplasmosis

• Cytomegalovirus

• Kaposi sarcoma

• Lymphoma (including lymphocytic interstitial pneumonitis)

• Pulmonary embolism

Diagnosis

Laboratory Tests

• Arterial blood gas shows hypoxemia and hypocapnia; peripheral oxygen saturation may be normal at rest but decreases rapidly with exercise

• Serologic tests not helpful

• Measurement of serum (1,3)-beta-D-glucan levels has good sensitivity and specificity

• Culture not possible

• Polymerase chain reaction (PCR) of bronchoalveolar lavage (BAL) is overly sensitive

  • Can be positive in colonized, noninfected persons

  • However, quantitative values may help with identifying infected patients

  • Negative PCR from BAL rules out disease

Imaging Studies

• Chest radiograph

  • Usually shows diffuse interstitial infiltrates, but early in infection, these may be heterogeneous, miliary, or patchy

  • May also show diffuse or focal consolidation, cystic changes, nodules, or cavitation within nodules

  • Pleural effusions not seen

• Chest radiograph is normal in 5–10%; high-resolution chest CT better able to demonstrate mild disease

• Upper lobe infiltrates common if patient received aerosolized pentamidine prophylaxis

Diagnostic Procedures

• Open lung biopsy and needle lung biopsy are infrequently required but may aid in diagnosing a granulomatous form of Pneumocystis pneumonia

• If induced sputum is negative and suspicion is high, diagnostic specimens may be obtained by bronchoalveolar lavage (sensitivity 86–97%) or, if necessary, by transbronchial lung biopsy (sensitivity ...