Parvimonas micra: A potential causative pathogen to consider when diagnosing odontogenic brain abscesses

Brain abscess is a life-threatening entity which requires prompt and long-term antibiotic therapy, generally associated with surgical drainage, and eradicating the primary source of infection. Parvimonas micra (Pm) has only been reported once before as the lone infecting organism of an orally originated, solitary brain abscess. Diagnosing brain abscesses caused by this Gram-positive anaerobic coccus, constituent of the oral cavity flora, is challenging, and an optimal treatment regimen has not been well established. We report the diagnosis and successful treatment of a Pm caused odontogenic brain abscess.

A 62-year-old immunocompetent male with a right-parietal brain abscess presented with headache and seizures. He was started on empirical antibiotic therapy and subsequently underwent surgical drainage. The only source of infection found was severe periodontitis with infected mandibular cysts. Thus, tooth extraction and cyst curettage were performed 1 week after brain surgery. Cultures of brain abscess fluid were negative, but amplification of bacterial 16S ribosomal RNA (rRNA) with polymerase chain reaction demonstrated Pm. After 3 weeks of intravenous ceftriaxone and metronidazole, the patient was switched to oral metronidazole and moxifloxacin for 6 weeks.

This case highlights the potential risk of untreated dental infections causing brain abscesses. Pm should be considered as a possible pathogen of odontogenic brain abscesses despite its presence usually not being detected by standard bacterial cultures. Therefore, 16S rRNA gene sequencing analysis is strongly recommended for bacterial identification before defining brain abscesses as cryptogenic.