Clinical Features:
The symptoms of Pneumocystis pneumonia (PCP) include dyspnea, nonproductive cough, and fever.  Chest radiography demonstrates bilateral infiltrates.  Extrapulmonary lesions occur in a minority (<3%) of patients, involving most frequently the lymph nodes, spleen, liver, and bone marrow.  Typically, in untreated PCP increasing pulmonary involvement leads to death.

Laboratory Diagnosis:
The specific diagnosis is based on identification of P. jirovecii in bronchopulmonary secretions obtained as induced sputum or bronchoalveolar lavage (BAL) material.  In situations where these two techniques cannot be used, transbronchial biopsy or open lung biopsy may prove necessary.  Microscopic identification of P. jiroveci trophozoites and cysts is performed with stains that demonstrate either the nuclei of trophozoites and intracystic stages (such as Giemsa) or the cyst walls (such as the silver stains).  In addition, immunofluorescence microscopy using monoclonal antibodies can identify the organisms with higher sensitivity than conventional microscopy.

Diagnostic findings

• Microscopy
• Molecular methods

Treatment:
Trimethoprim-sulfamethoxazole is the drug of choice.  Recommended alternatives include pentamidine; trimethoprim plus dapsone*; atovaquone; and primaquine* plus clindamycin*.  For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).

* This drug is approved by the FDA, but considered investigational for this purpose.