Pneumocystis jirovecii pneumonia (PJP)

A 33 year old male with a known history of HIV infection presents to the emergency department with a 7 day history of progressive shortness of breath, dry cough, and fever. His CD4 count is 90 cells/μL despite being on antiretroviral therapy. On examination, blood pressure is 110/70 mm Hg, pulse rate is 108 beats per minute, respiratory rate is 22 breaths per minute, oxygen saturation is 92% on room air, and temperature is 100.9 F. Lung auscultation reveals bilateral crackles, although examination may be normal in some cases. There is no peripheral edema or lymphadenopathy. Laboratory evaluation shows a normal leukocyte count with lymphopenia. Chest X ray shows diffuse bilateral perihilar interstitial infiltrates, and CT scan demonstrates bilateral ground glass opacities. Arterial blood gas shows respiratory alkalosis with hypoxemia (PaO2 50 mm Hg) and an increased A–a gradient. Bronchoalveolar lavage with silver stain reveals disc shaped cysts. Diagnosis?

Diagnosis is Pneumocystis jirovecii pneumonia.

1. Definition

Pneumocystis jirovecii pneumonia (PJP) is an opportunistic fungal infection that primarily affects immunocompromised patients, especially those with HIV infection with CD4 < 200 cells/μL.

2. Etiology

2.1 Major Risk Factors

1. HIV infection with CD4 < 200 cells/μL
2. Chronic glucocorticoid use
3. Immunosuppressive therapy
4. Hematologic malignancies and organ transplantation

3. Pathophysiology

1. Organism attaches to type I alveolar epithelium
2. Causes host mediated inflammatory response leading to diffuse alveolar damage
3. Results in impaired gas exchange, hypoxemia, and possible respiratory failure

4. Clinical Features

1. Subacute onset over days to weeks in HIV patients
2. Fever, dry cough, and progressive dyspnea
3. Tachypnea, tachycardia, and hypoxemia
4. Lung examination may be normal in up to 50% of cases or show crackles

5. Diagnostic Evaluation

5.1 Imaging

1. Chest X ray shows diffuse bilateral perihilar interstitial infiltrates
2. CT chest shows ground glass opacities, highly sensitive

5.2 Laboratory Findings

1. Elevated LDH
2. Elevated beta D glucan
3. Hypoxemia with increased A–a gradient

5.3 Microbiological Diagnosis

1. Bronchoalveolar lavage or induced sputum
2. Identification by silver stain, PCR, or immunofluorescence

6. Key Diagnostic Insight

HIV with CD4 < 200 + subacute dyspnea + ground glass opacities + hypoxemia = Pneumocystis jirovecii pneumonia

7. Management

7.1 First Line Treatment

1. Trimethoprim sulfamethoxazole (TMP SMX) for 21 days

7.2 Indications for Adjunctive Corticosteroids

1. PaO2 ≤ 70 mm Hg
2. A–a gradient ≥ 35 mm Hg
3. Start within 72 hours in moderate to severe disease

7.3 Additional Measures

1. Initiate or optimize antiretroviral therapy within 2 weeks once stable

8. Prophylaxis

1. TMP SMX prophylaxis in patients with CD4 < 200 cells/μL
2. Also indicated in CD4 < 14% or oropharyngeal candidiasis

9. Complications

1. Respiratory failure
2. Pneumothorax
3. Rare extrapulmonary involvement
4. High mortality in severe disease

10. Key Clinical Insight 

HIV with CD4 < 200 presenting with subacute dyspnea, dry cough, and hypoxemia strongly suggests Pneumocystis jirovecii pneumonia

11. Exam Level Pearls

1. Ground glass opacities are classic
2. Dry cough with hypoxemia is typical
3. Normal lung exam does not exclude disease
4. Steroids reduce mortality in moderate to severe cases
5. TMP SMX is both treatment and prophylaxis