Abstract Introduction Pneumonia remains a leading cause of mortality following autologous stem cell transplantation (ASCT), particularly during the early post-transplantation period. While bacterial infections are most prevalent, viral and fungal pathogens pose substantial diagnostic challenges due to nonspecific clinical presentations, frequent co-infections, and the potential for rapid deterioration in immunocompromised hosts. Previous studies have demonstrated a high diagnostic yield of bronchoscopy with bronchoalveolar lavage (BAL) in this population; however, mortality rates remain elevated despite the initiation of targeted antimicrobial therapy. Case A 53-year-old patient with a history of central nervous system lymphoma status post (s/p) ASCT three months prior, recent cytomegalovirus viremia two weeks earlier on valganciclovir, and end-stage renal disease secondary to IgA nephropathy s/p three renal transplants on chronic prednisone presented with fever, dysuria, and a three-month history of cough. Prophylactic sulfamethoxazole-trimethoprim (SXT) had been discontinued shortly before the transplant to initiate methotrexate. Chest CT showed patchy ground-glass opacities in the lower lobes. The respiratory viral panel was positive for enterovirus and rhinovirus. Given a positive Fungitell and elevated LDH, BAL confirmed Pneumocystis jirovecii pneumonia (PCP) and revealed a weakly positive Histoplasma antigen (0.6 ng/mL; normal 0.2) without eosinophilia. SXT and itraconazole were initiated, but Itraconazole was discontinued after 6 days following negative serum and urine Histoplasma antigens. Prednisone was increased for severe PCP, but the patient failed to improve and developed acute respiratory distress syndrome (ARDS) requiring intubation. Steroids were escalated to hydrocortisone 100 mg every six hours, and SXT was switched to primaquine and clindamycin for suspected treatment failure. A repeat BAL showed only commensal flora. Given the severity of her condition, the family opted against further escalation of care, and the patient passed away. Discussion This case underscores the complexity of diagnosing and managing pneumonia following ASCT. Although bacterial infections predominate in the early post-transplant period, opportunistic pathogens such as PCP may emerge months later, particularly after interruption of prophylaxis. In prior ASCT cohorts, BAL has identified causative pathogens in 30-50% of undiagnosed pneumonias; however, mortality remains above 40%, especially in cases complicated by ARDS. The weakly positive Histoplasma antigen result in this case highlights the difficulty of interpreting low-titer findings in immunocompromised hosts. Maintaining early clinical suspicion and pursuing comprehensive microbiologic evaluation are critical in these patients. Even with prompt empiric therapy and early culture-directed therapy, polymicrobial pneumonia in this population often carries a poor prognosis, particularly after the onset of respiratory failure. This abstract is funded by: None
Morato et al. (Fri,) studied this question.