Radiographic features in investigated for Pneumocystis jirovecii pneumonia: a nested case-control study.

Background: Pneumocystis jirovecii pneumonia (PJP) can be challenging to diagnose, often requiring bronchoscopy. Since most patients suspected of PJP undergo imaging, we hypothesized that the findings of these studies could help estimate the probability of disease prior to invasive testing.

Methods: We created a cohort of patients who underwent bronchoscopy specifically to diagnose PJP and conducted a nested case-control study to compare the radiographic features between patients with (n = 72) and without (n = 288) pathologically proven PJP. We used multivariable logistic regression to identify radiographic features independently associated with PJP.

Results: Chest x-ray findings poorly predicted the diagnosis of PJP. However, multivariable analysis of CT scan findings found that "increased interstitial markings" (OR 4.3; 95%CI 2.2-8.2), "ground glass opacities" (OR 3.3; 95%CI 1.2-9.1) and the radiologist's impression of PJP being "possible" (OR 2.0; 95%CI 1.0-4.1) or "likely" (OR 9.3; 95%CI 3.4-25.3) were independently associated with the final diagnosis (c-statistic 0.75).

Conclusions: Where there is clinical suspicion of PJP, the use of CT scan can help determine the probability of PJP. Identifying patients at low risk of PJP may enable better use of non-invasive testing to avoid bronchoscopy while higher probability patients could be prioritized.