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

Area of Science:

• Medical Mycology
• Infectious Diseases
• Dermatopathology

Background:

• Rothia mucilaginosa, once considered a harmless oral commensal, is now recognized as an opportunistic pathogen.
• Invasive infections by R. mucilaginosa are increasingly reported in immunocompromised individuals, especially those with hematolymphoid malignancies and neutropenia.
• Cutaneous involvement by R. mucilaginosa is underrepresented and poses diagnostic challenges due to ambiguous morphology and nonspecific stain results.

Purpose of the Study:

• To describe the histopathologic features of cutaneous Rothia mucilaginosa infections.
• To highlight diagnostic pitfalls in identifying R. mucilaginosa in skin biopsies.
• To emphasize the utility of immunohistochemistry in differentiating R. mucilaginosa from mimics.

Main Methods:

• Retrospective analysis of three cases of suspected or confirmed cutaneous R. mucilaginosa infection in immunocompromised patients.
• Histopathologic examination of skin biopsies using special stains (PAS, GMS, Gram).
• Review of clinical data, including outcomes and microbiological findings; utilization of CD61 immunohistochemistry for differential diagnosis.

Main Results:

• R. mucilaginosa presented as small, round eosinophilic cocci within vascular spaces and papillary dermis.
• Organisms showed variable positivity with PAS, GMS, and Gram stains.
• A diagnostic pitfall involving platelet aggregates mimicking R. mucilaginosa was identified; CD61 IHC was crucial for differentiation.

Conclusions:

• Rothia mucilaginosa should be considered in the differential diagnosis of cutaneous infections in immunocompromised patients.
• Histopathologic features, nonspecific special stains, and potential mimics like platelet aggregates require careful evaluation.
• Adjunct immunohistochemical studies, such as CD61, are valuable for accurate diagnosis and avoiding misinterpretation.