An Atypical Presentation of Ecthyma Gangrenosum in a Patient With Waldenström Macroglobulinemia

Ecthyma gangrenosum (EG) is a relatively rare cutaneous infection that is most commonly caused by <i>Pseudomonas aeruginosa (P. aeruginosa)</i>. EG predominantly affects immunocompromised individuals and can be categorized into bacteremic and non-bacteremic types. Despite this distinction and clinical evidence supporting the existence of the non-bacteremic type of EG, the long-held belief that bacteremia must be present for the diagnosis of EG persists. This report describes a case of a 78-year-old Caucasian male with Waldenström macroglobulinemia (WM) undergoing chemotherapy, who presented with a non-tender, necrotic, gangrenous ulcer on the left side of his groin. Physical examination revealed a sharply demarcated black eschar measuring 3 cm in diameter with an erythematous border. Laboratory results showed a white blood cell count of 1.34 K/mcL, red blood cell count of 4.07 million/µL, and platelet count of 126 K/mcL, indicating marked pancytopenia. Blood cultures obtained on the day of admission were negative. Tissue cultures from a punch biopsy were positive for <i>P. aeruginosa</i> and <i>Enterococcus faecalis (E. faecalis)</i>. Initial empiric treatment consisted of intravenous cefepime and vancomycin. Full surgical debridement was performed on day four. Following the procedure, the patient was discharged the same day on amoxicillin-clavulanate and ciprofloxacin to be taken for 10 days and was instructed to follow up with wound care. The lesion site showed improvement with the antibiotic regimen, both before and after debridement. EG can manifest without bacteremia, especially in immunosuppressed individuals with environmental risk factors. In this case, the patient's history of WM, use of the chemotherapeutic agent zanubrutinib, and neutropenia compromised innate host defenses. These factors, combined with a recent hospitalization that included the administration of broad-spectrum antibiotics, created a favorable environment for bacterial growth. This report serves as a reminder that prompt initiation of empiric antibiotics, timely biopsy of the lesion, and subsequent tissue cultures to determine bacterial susceptibility are essential for a favorable outcome when non-bacteremic EG is suspected.