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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


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 ...

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