Invasive Pulmonary Aspergillosis-Mimicking Pseudomonas aeruginosa Pneumonia in Immunocompromised Patients: Radiologic Differentiation.

BACKGROUND: Pseudomonas aeruginosa (PA) pneumonia is occasionally misdiagnosed as invasive pulmonary aspergillosis (IPA) in immunocompromised patients because of shared risk factors and overlapping radiologic manifestations. However, this topic has not been systematically investigated. METHODS: We retrospectively reviewed immunocompromised patients diagnosed with PA pneumonia between 2014 and 2023. Patients with confirmed or probable PA pneumonia were analyzed. For comparison, control patients with proven or probable IPA diagnosed between 2018 and 2023 were randomly selected. First, we tested whether two thoracic radiologists could differentiate PA pneumonia from IPA based on computed tomography (CT) findings. Second, we identified clinical and radiologic features that could help differentiation. RESULTS: Thirty-three PA patients (15 confirmed and 18 probable) and 75 IPA control patients (15 proven and 60 probable) were analysed. Two radiologists blindly scored 33 PA and 25 IPA cases which were randomly selected from control patients. Among PA pneumonia cases, 36% (12/33) were unanimously misclassified as IPA by the two radiologists. The sensitivities of radiologist A and B for PA were 61% and 33%, respectively (fair agreement, kappa value = 0.38). We then compared the clinical features and CT findings of the 33 PA and 75 IPA patients. Clinical factors such as solid organ transplantation beyond 6 months and an acute clinical course favored PA diagnosis. PA pneumonia frequently exhibited IPA-like features, including macronodules (39%), mass-shaped consolidation (49%), and cavitation (24%). However, ill-defined centrilobular nodules and peribronchial consolidation were significantly more common in PA pneumonia (67% vs. 21% and 58% vs. 21%, respectively, P < 0.001). In multivariate analysis, solid organ transplantation, peribronchial consolidation, and ill-defined centrilobular nodules were independent predictors of PA pneumonia. CONCLUSION: Approximately one-third of patients with PA pneumonia exhibited CT findings resembling IPA. Integration of clinical contexts, especially transplant history and detailed interpretation of radiologic signs, may improve differential diagnosis between PA pneumonia and IPA.