From Flora to Threat: Septic Emboli Due to Corynebacterium pseudodiphtheriticum in a Patient With Relapsed Acute Myeloid Leukemia.

Corynebacterium pseudodiphtheriticum (C. pseudodiphtheriticum) is typically a benign inhabitant of the upper respiratory tract but has recently emerged as a potential opportunistic pathogen in immunocompromised individuals. We report a rare case of disseminated C. pseudodiphtheriticum infection in a 60-year-old man with relapsed acute myeloid leukemia (AML) undergoing chemotherapy. The patient developed fever, hypotension, and a diffuse papular rash in the setting of profound neutropenia. Blood cultures from central and peripheral lines grew C. pseudodiphtheriticum, and computed tomography (CT) revealed multiple bilateral pulmonary nodules with ground-glass and tree-in-bud opacities, suggestive of septic emboli. Despite the organism's frequent dismissal as a contaminant, the clinical picture, imaging, and response to therapy supported its role as the causative pathogen. Following the administration of broad-spectrum antibiotics, removal of the peripherally inserted central catheter (PICC) line, and a course of oral linezolid, the patient experienced rapid clinical and radiographic improvement. This case highlights the pathogenic potential of C. pseudodiphtheriticum. It underscores the need to recognize it as a true pathogen in neutropenic patients, particularly those with indwelling catheters and signs of embolic disease.