Pneumocystis jiroveci pneumonia (also known as Pneumocystis pneumonia, or PCP; formerly P carinii pneumonia) is caused by the ubiquitous unicellular eukaryote, P jiroveci. This organism is a rare cause of infection in the general population, but it is a frequent cause of morbidity and mortality in persons who are immunocompromised, especially patients with acquired immunodeficiency syndrome (AIDS).
PCP is classified as a fungal pneumonia but does not respond to antifungal therapy. The incidence of PCP has decreased as a result of and highly active antiretroviral therapy (HAART).(See the images below.)
Patients who do not have AIDS but are immunocompromised and at risk for P jiroveci pneumonia include individuals with hematologic malignancies
; organ transplant recipients
; and those receiving long-term steroid or cytotoxic therapy, including patients with systemic vasculitis or other autoimmune deficiency. Other patients with immune deficiency disorders who are at particular risk for PCP include those with thymic dysplasia, those with severe combined immunodeficiency, and those with hypogammaglobulinemia. Severe malnutrition may predispose patients to PCP.
A subset of patients present with atypical clinical and radiographic features termed chronic PCP. These patients have a prolonged clinical course over months or years, with persistent stable symptoms and radiographic abnormalities corresponding to pathologic findings of interstitial fibrosis, traction bronchiectasis, and honeycombing.
Chest radiographs should be included in the initial evaluation for PCP. Frequently, these are the only images required. High-resolution computed tomography (HRCT) scanning and, occasionally, gallium-67 (67Ga) scanning are useful in symptomatic patients in whom chest radiograph findings are normal or equivocal.
The hallmark finding of PCP on HRCT scans is diffuse ground-glass opacity (GGO), which reflects the accumulation of intra-alveolar fibrin, debris, and organisms.
The term ground-glass refers to parenchymal opacification, which does not obscure the underlying pulmonary architecture. This usually occurs in a bilateral, symmetrical, predominantly perihilar distribution and may be geographic or mosaic in appearance, with areas of normal lung adjacent to areas of affected lung.
A study of 32 patients with AIDS-related PCP showed a a central distribution of ground-glass opacity with relative peripheral sparing in 41% of patients, a mosaic pattern in 29%, and a diffuse distribution in 24%.
Chest radiography retains a key role in the diagnosis of pneumonia in the immune compromised.
Chest radiography retains its position as the prime modality in the diagnosis and exclusion of pneumonia, follow-up imaging to check for resolution, and to evaluate potential complications. CT scanning is more sensitive and, with certain infections, more specific. MRI provides an option for monitoring progress, although it cannot yet replace chest radiography or CT scanning as the initial diagnostic procedure.
This radiograph depicts a diffuse, fine, reticular opacification as a result of Pneumocystis jiroveci pneumonia.
This chest radiograph shows bilateral upper-lobe pneumatoceles after a Pneumocystis jiroveci infection in a patient with acquired immunodeficiency syndrome.
A magnified view of lung apices from a patient with human immunodeficiency virus infection. This image shows the redistribution of Pneumocystis jiroveci pneumonia to the upper lobes following aerosolized pentamidine prophylaxis.
High-resolution CT (HRCT) scan in a 32-year-old man with HIV infection showing ground-glass appearance due to Pneumocystis jiroveci pneumonia.
In a study of 105 non-AIDS PCP immunocompromised patients, chest radiographic findings wre divided into 3 stages: early stage (normal or nearly normal chest radiograph), mid-stage (bilateral pulmonary infiltrates), and late stage (bilateral pulmonary consolidations). Chest HRCT findings were also divided into 3 stages: early stage (bilateral diffuse ground-glass opacity [GGO]), mid-stage (bilateral diffuse GGO and patchy consolidations), and late stage (bilateral diffuse consolidations).
Limitations of techniques
Chest radiograph findings may be normal in 10-39% of patients with PCP. With CT and 67Ga scanning, the appearance of PCP is nonspecific.
For excellent patient education resources, visit eMedicineHealth’s Lung Disease and Respiratory Health Center and Sexual Health Center. Also, see eMedicineHealth’s patient education articles Viral Pneumonia, Acute Respiratory Distress Syndrome, HIV/AIDS, and HIV Testing.