Actinomyces viscosus causing disseminated disease in a patient on methotrexate

Actinomycosis is an uncommon infectious disease caused predominantly by Actinomyces israelii. Actinomycosis usually involves the cervicofacial, thoracic, abdominal, and pelvic region, dissemination is uncommon. Actinomyces viscosus are commensal organisms that make up the normal flora of the oropharynx of humans and has rarely been reported to cause disease. Here, we report a unique case of disseminated actinomycosis with lung and brain lesions caused by Actinomyces viscosus resembling lung cancer with metastasis in a 74 year old male. Cultures from skin lesions confirmed A. viscosus. Although the patient was immunocompromised, antibiotic treatment with a penicillin-based regimen was effective.