A69-05 A Diagnostic Challenge: Pneumocystis Jirovecii Pneumonia Presenting as Interstitial Lung Disease in an Undiagnosed HIV Patient

Abstract Introduction Pneumocystis jirovecii pneumonia (PCP) remains one of the most common opportunistic infections among individuals with HIV/AIDS. It also occurs in patients with other causes of immunosuppression, including organ transplantation, malignancy, or autoimmune diseases treated with corticosteroids, methotrexate, or other immunosuppressants. Diagnosis can be challenging due to its nonspecific clinical and radiographic presentation, which overlaps with other infectious and noninfectious pulmonary conditions such as drug-induced pneumonitis, diffuse alveolar hemorrhage, or interstitial lung disease (ILD). These diagnostic ambiguities can delay recognition and treatment, especially in patients with uncertain immune status or complex pulmonary histories. Case Description A 28-year-old female with a history of hypersensitivity pneumonitis (HP) presented from an outside hospital with acute hypoxic respiratory failure for evaluation of possible interstitial lung disease (ILD) exacerbation and lung transplant candidacy. On admission, she developed recurrent fevers and worsening oxygen requirements, prompting initiation of empiric antibiotics. Laboratory studies were notable for leukocytosis (WBC 15.5 ×109/L) and elevated CRP (30.68 mg/L), with otherwise unremarkable results. Chest CT revealed diffuse ground-glass opacities with interlobular septal thickening and a right-sided pneumothorax. Given her history of vaping, exposure to lead solder fumes, and occupational contact with various chemicals, there was high suspicion for underlying ILD. Despite empiric antibiotics and high-dose corticosteroids, her respiratory status continued to deteriorate. Further infectious evaluation, including a Karius test, was positive for Pneumocystis pneumonia PCP. An immunodeficiency panel subsequently returned positive for HIV, with a quantitative PCR of 114,000 copies/mL. Lung biopsy demonstrated PCP pneumonia with mild acute lung injury changes without histologic evidence of ILD. Despite initiation of targeted antimicrobial and antiviral therapy, the patient’s condition continued to worsen, requiring ICU transfer and initiation of extracorporeal membrane oxygenation (ECMO) where her care remains ongoing. Discussion PCP continues to pose significant diagnostic and therapeutic challenges, particularly in patients without known immunodeficiency. Although its incidence has declined with effective HIV therapy and prophylaxis, PCP still occurs in 20-30% of untreated HIV-positive individuals and in those receiving chronic immunosuppression for non-HIV conditions. This case underscores the importance of maintaining a broad differential diagnosis in patients with atypical pulmonary presentations and uncertain immune status. The overlapping features of HP, environmental exposures, and immunosuppression obscured the underlying infection, delaying appropriate therapy. Early recognition of PCP, even in patients with presumed noninfectious lung disease, remains essential for improving outcomes. This abstract is funded by: None