Pneumocystis Jirovecii Infection

Key Features

Essentials of Diagnosis

• Significant immunosuppression

• Fever, tachypnea, cough, dyspnea

• Hypoxemia; diffuse interstitial infiltrates

• Detection of the organism in specimens of pulmonary origin

General Considerations

• Initial infection is presumed to occur asymptomatically via inhalation, usually in early childhood, and to become a clinical problem upon reactivation during immune suppression

• Severe signs and symptoms occur chiefly in patients with abnormal T-cell function, such as hematologic malignancies and organ transplantation

• Pneumocystis also causes severe pneumonia in patients with γ-globulin deficiency and is an AIDS-defining illness for children with advanced HIV infection

Clinical Findings

Symptoms and Signs

• In most patients, a gradual onset of fever, tachypnea, dyspnea, and mild, nonproductive cough occurs over 1–4 weeks

• Initially the chest is clear, although retractions and nasal flaring are present

• Hypoxemia out of proportion to the clinical and radiographic signs is an early finding; however, even minimally decreased arterial oxygen pressure values should suggest this diagnosis in immunosuppressed children

• In some children with AIDS or severe immunosuppression from chemotherapy or organ transplantation, the onset may be abrupt and progression more rapid

• Acute dyspnea with pleuritic pain may indicate the complication of pneumothorax

Differential Diagnosis

• Influenza

• Respiratory syncytial virus

• Cytomegalovirus

• Adenovirus

• Other viral infections

• Bacterial and fungal pneumonia

• Pulmonary emboli or hemorrhage

• Heart failure

• Chlamydophila pneumoniae

• M pneumoniae infections

Diagnosis

Laboratory Findings

• Serum lactate dehydrogenase levels may be elevated markedly as a result of pulmonary damage

• In moderately severe cases, the arterial oxygen pressure is < 70 mm Hg or the alveolar-arterial gradient is < 35 mm Hg

Imaging

• Chest radiographs

  • Normal early in disease course

  • Classic pattern seen on later films: bilateral, interstitial, lower lobe alveolar disease starting in the perihilar regions, without effusion, consolidation, or hilar adenopathy

• High-resolution CT scanning may reveal extensive ground-glass attenuation or cystic lesions

• Older HIV-infected patients present with other patterns, including nodular infiltrates, lobar pneumonia, cavities, and upper lobe infiltrates

Diagnostic Procedures

• Diagnosis requires finding characteristic round (6–8 mm) cysts in a lung biopsy specimen, bronchial brushings, alveolar washings, induced sputum, or tracheal aspirates

• Tracheal aspirates are less sensitive, but are more rapidly and easily obtained

• Several rapid stains—as well as the standard methenamine silver stain—are useful

• Indirect fluorescent antibody method is most sensitive

Treatment

General Measures

• Supplemental oxygen and nutritional support may be needed

• Patient should be in respiratory isolation

Specific Measures

• Trimethoprim-sulfamethoxazole is drug of choice

  • Dosage: 20 mg/kg/d of trimethoprim and 100 mg/kg/d of sulfamethoxazole in four divided doses intravenously or orally if well ...