When Pneumonia is One-Sided: A Rare Unilateral Progressive Pneumocystis jirovecii Pneumonia Case

Objective: To report a case of Pneumocystis jirovecii Pneumonia (PJP) characterized by predominant unilateral pulmonary infiltration, and to explore its pathogenic specificity and clinical management in combination with airway structural abnormalities.​ Methods: We retrospectively analyzed the clinical data of a post-renal transplantation patient with PJP admitted to Xuanwu Hospital, Capital Medical University, including medical history, imaging features, etiological results, treatment process and prognosis. A hypothesis regarding the pathogenic mechanism was proposed based on airway examination findings.​ Results: A 60-year-old male with a 1-year history of renal transplantation and long-term immunosuppressant use was admitted due to "cough and expectoration for 2 weeks". Admission CT showed severe exudation in the right lung and left lower lobe, which was confined to the right lung. Bronchoscopy revealed left airway stenosis, and next-generation sequencing (NGS) of bronchoalveolar lavage fluid (BALF) detected Pneumocystis jirovecii and two viruses. Despite immunosuppressant withdrawal and targeted anti-infective therapy, the patient developed type I respiratory failure. After ineffective treatment with prone position ventilation, tracheal intubation, mechanical ventilation and nitric oxide (NO) inhalation, venovenous extracorporeal membrane oxygenation (VV-ECMO) was initiated for 25 days. Multiple imaging examinations during treatment consistently showed that the lesion was mainly in the right lung, with slow progression of exudation in the left lung.​ Conclusion: This PJP case presented with rare unilateral infiltration progression. Left airway stenosis may interfere with the pathogenic process of pathogens through airway hydrodynamic changes, providing a new perspective for PJP pathogenesis research.​