DESCRIPTION

• Originally called Pneumocystis carinii pneumonia, then renamed Pneumocystis jirovecii but still referred to as PCP
• Most common opportunistic infection in patients with HIV, even with PCP prophylaxis and antiretroviral therapy
• Believed to be transmitted by respiratory-aerosol route:
  • Cysts colonize respiratory tract.
  • Cysts rupture and multiple trophozoites release and form foamy exudate in alveoli.
• Most cases are believed to represent reactivation of latent disease, although person-to-person transmission suggested.
• Actual mode of transmission is unclear.

ETIOLOGY

• Pneumocystis is classified as a fungus.
• Pneumocystis occurs in hosts with altered cellular immunity:
  • HIV infection (most common, especially when CD4 count < 200 cells/mm³)
  • Cancer
  • Corticosteroid treatment
  • Organ transplantation
  • Malnutrition

Pediatric Considerations

PCP in children is typically more severe.

[Outline]

• DESCRIPTION
• ETIOLOGY

SIGNS AND SYMPTOMS

• Subacute presentation
• Up to 7% of patients can be asymptomatic.
• Patients on inhaled pentamidine prophylaxis may have milder symptoms:
  • Increased incidence of pneumothorax
  • Increased incidence of extrapulmonary disease

History

• Fever
• Cough with none or minimal amount of white sputum
• Dyspnea on exertion or at rest:
  • Progressive over days (most common in non–HIV-immunocompromised hosts)
  • Indolent, developing over weeks to months (more common in HIV-positive hosts)
  • Oxygen desaturation with exercise
• Chills
• Fatigue
• Weight loss
• Chest pain

Physical Exam

• Tachypnea
• Tachycardia
• Crackles and rhonchi on lung exam

ESSENTIAL WORKUP

• CBC
• Electrolytes
• Arterial blood gas (ABG)
• Lactate dehydrogenase (LDH)
• Blood cultures
• Chest x-ray

DIAGNOSIS TESTS & INTERPRETATION

Lab

• ABG:
  • Obtain in all cases of PCP.
  • Calculate the alveolar–arterial (A–a) gradient (usually increased).
  • Adjunctive corticosteroid therapy for A–a gradient > 35 mm Hg or PaO₂ < 70 mm Hg
• LDH:
  • Elevated in HIV-positive patients with PCP compared to non-PCP pneumonia
  • Higher levels correlate with poorer prognosis.

Imaging

• Chest radiograph:
  • Classically reveals bilateral interstitial or central alveolar infiltrates
  • Radiograph normal in up to 25% of patients with PCP
  • Early or mild infection associated with decreased sensitivity
  • Atypical presentations include:
    • Lobar infiltrates
    • Cysts
    • Pneumothoraces
    • Pleural effusions
    • Nodular infiltrates
  • Prophylaxis with aerosolized pentamidine is a risk factor for developing predominantly upper lobe.
  • Chest radiograph abnormalities can persist for months after treatment.
• High-resolution chest CT:
  • High sensitivity for PCP in HIV-positive patients.
  • Reveals patchy ground-glass attenuation

Diagnostic Procedures/Surgery

• Induced sputum:
  • Definitive diagnosis requires presence of Pneumocystis organisms in an appropriately stained respiratory specimen.
  • Specificity approaches 100%, but sensitivity depends on quality of induced sputum and lab expertise.
  • Less sensitive in patients on inhaled pentamidine prophylaxis and non–HIV-positive patients
• Bronchoalveolar lavage:
  • Perform if the induced sputum is nondiagnostic and the suspicion for PCP is still high.
  • Sensitivity 80–100%

DIFFERENTIAL DIAGNOSIS

Constellation of dyspnea, fever, diffuse radiographic infiltrates, minimal or nonproductive cough, and slow progressive course suggests atypical cause of the pneumonia:

• Chlamydia pneumoniae
• Legionella
• Mycoplasma
• Tuberculosis
• Viral pneumonia (especially cytomegalovirus)

[Outline]

• SIGNS AND SYMPTOMS
• ESSENTIAL WORKUP
• DIAGNOSIS TESTS & INTERPRETATION
• DIFFERENTIAL DIAGNOSIS

PRE-HOSPITAL

Provide supplemental oxygen for symptomatic patients.

INITIAL STABILIZATION/THERAPY

• ABCs
• Provide adequate oxygenation with nasal cannula up to 100% nonrebreather.
• Perform endotracheal intubation in those with refractory hypoxemia despite maximal oxygenation or hypercarbic respiratory failure.
• At least 500–1,000 cc 0.9% normal saline IV bolus for hypotension, sepsis, dehydration

ED TREATMENT/PROCEDURES

• Initiate antibiotics:
  • IV Bactrim is the first-line agent.
  • IV pentamidine for those who cannot tolerate Bactrim
  • Oral therapy is an option for well-appearing patients.
  • Alternative regimens include trimethoprim–dapsone, clindamycin–primaquine, and atovaquone.
  • Continue antibiotics for 21 days.
• Adjunctive corticosteroids in patients with A–a gradient > 35 mm Hg or PaO₂ < 70 mm Hg:
  • Must start within 1st 72 hr of treatment
• Isolate suspected PCP patients from others who are immunocompromised.

MEDICATION

• Atovaquone: 750 mg (peds: Dosing not established) PO q12h
• Clindamycin/primaquine: Clindamycin 900 mg (peds: Dosing not established) IV q8h or 300–450 mg PO q6h and primaquine 15–30 mg (peds: Dosing not established) PO per day
• Pentamidine: 4 mg/kg/24h IV over 1 hr (peds: 3–4 mg/kg IM or IV once/day for 21 days)
• Prednisone: 40 mg (peds: Dosing not established) PO q12h for 5 days, 40 mg PO per day for 5 days, then 20 mg PO per day for 11 days (IV methylprednisolone at 75% of the prednisone dose may be substituted)
• Trimethoprim/dapsone: Trimethoprim 15–20 mg/kg/d IV div. q8h + dapsone 100 mg PO per day (peds: Dosing not established)
• Trimethoprim/sulfamethoxazole (Bactrim): Trimethoprim 15–20 mg/kg/d IV div. q6h and sulfamethoxazole 100 mg/kg/d IV div. q6h (peds: Dosing same)

Pediatric Considerations

• Treatment of choice is IV trimethoprim/sulfamethoxazole, followed by IV pentamidine.
• Dosing for alternative medications not yet established (consult pediatric infectious disease specialist).

[Outline]

• PRE-HOSPITAL
• INITIAL STABILIZATION/THERAPY
• ED TREATMENT/PROCEDURES
• MEDICATION

DISPOSITION

Admission Criteria

• Moderate to severe disease (PaO₂ < 70 mm Hg or A–a gradient > 35 mm Hg)
• Inability to digest medications
• Inability to return for careful follow-up

Discharge Criteria

• Nontoxic clinical appearance
• Mild disease state (no hypoxemia or A–a gradient)
• Ability to tolerate medications
• Close follow-up arranged
• If results of induced sputum are not available, add macrolide to empirical regimen.

FOLLOW-UP RECOMMENDATIONS

Close follow-up must be arranged with infectious disease specialist to allow for outpatient management.

[Outline]

• DISPOSITION
• FOLLOW-UP RECOMMENDATIONS

• Include PCP in differential diagnosis in any patient presenting with shortness of breath who is immunocompromised or is suspected of having undiagnosed HIV.
• Patients considered for PCP are also more likely to have TB or atypical bacterial pneumonia.
• Well-appearing patients with low oxygen saturations are at higher risk for complications.

ICD9

136.3 Pneumocystosis

ICD10

B59 Pneumocystosis

[Outline]

• ICD9
• ICD10

• Thomas CF Jr, Limper AH. Pneumocystis pneumonia. N Engl J Med. 2004;350:2487–2498.
• Huang L, Quartin A, Jones D, et al. Intensive care of patients with HIV infection. N Engl J Med. 2006;355:173–181.
• Kovacs JA, Masur H. Evolving health effects of Pneumocystis: One hundred years of progress in diagnosis and treatment. JAMA 2009;301:2578–2585.

See Also (Topic, Algorithm, Electronic Media Element)

• HIV/AIDS
• Pneumonia, Adult
• Pneumonia, Pediatric
• Tuberculosis

Alan M. Kumar