Case Series of Cutaneous Rothia Mucilaginosa Infection and an Important Potential Pitfall Case

Rothia mucilaginosa has emerged as an important opportunistic pathogen, challenging the traditional view of this organism as a harmless oral commensal. Invasive infections are increasingly recognized in immunocompromised patients, particularly those with hematolymphoid malignancies, solid organ, and stem cell transplants, and neutropenia. Cutaneous involvement, however, remains underrepresented and remains a diagnostic challenge in view of its ambiguous morphology in tissue sections and nonspecific special stains results. We report 3 cases of suspected or confirmed cutaneous involvement by R. mucilaginosa in immunocompromised patients with hematolymphoid malignancies and profound neutropenia. In all cases, the organisms appeared as small, round eosinophilic coccoid structures predominantly within the vascular spaces and forming aggregates within the papillary dermis. The organisms were positive on periodic acid-Schiff, Grocott methenamine silver, and gram stains, with some variable stain reactivity. One case demonstrated culture-proven R. mucilaginosa bacteremia with a fatal clinical course in the setting of systemic sepsis. In addition, we present a pitfall case in which platelet aggregates closely mimicked morphology of R. mucilaginosa aggregates, creating a potential diagnostic trap. In this context, CD61 immunohistochemistry was helpful in distinguishing platelet aggregates, which showed strong positivity, from R. mucilaginosa organisms, which were negative. Our findings highlight the importance of considering R. mucilaginosa in the differential diagnosis of cutaneous infections in immunocompromised patients and emphasize potential histopathologic pitfall. Awareness of the R. mucilaginosa morphologic features, its nonspecific findings on special stains and the use of adjunct immunohistochemical studies may help avoid misinterpretation and facilitate accurate diagnosis.