Title : PCR-guided diagnosis and intrathecal salvage therapy for capnocytophaga brain abscess with polymicrobial anaerobic ventriculitis in an immunocompetent host
Abstract:
Background: Brain abscess complicated by ventriculitis is a rare and life-threatening central nervous system (CNS) infection associated with high morbidity and mortality. While common pathogens include streptococci and anaerobic oral flora, Capnocytophaga species are uncommon causes of CNS infection, particularly in immunocompetent hosts and in the absence of prior animal exposure. Diagnosis is frequently challenged by the fastidious growth characteristics of anaerobic organisms and prior antibiotic exposure, often resulting in persistently negative cultures. Molecular diagnostic techniques have emerged as valuable tools for pathogen identification in culture-negative infections; however, data guiding their use and subsequent management strategies remain limited.
Case Presentation: We report a 69-year-old immunocompetent woman with chronic periodontitis who presented with altered mental status and was found to have a left temporal lobe brain abscess with mass effect. Initial surgical drainage identified Capnocytophaga species, and she completed prolonged intravenous antimicrobial therapy. She was subsequently transferred to our institution with recurrent fevers, encephalopathy, and headaches. MRI demonstrated a recurrent temporal abscess with extensive ependymal enhancement and intraventricular purulence consistent with ventriculitis. Despite multiple neurosurgical interventions and persistently neutrophilic cerebrospinal fluid (CSF), cultures remained negative.
Broad-range bacterial PCR sequencing of CSF identified polymicrobial anaerobic pathogens, including Prevotella species, Fusobacterium species, Streptococcus mitis, and Fannyhessea vaginae, implicating an oral source. Vancomycin-resistant Enterococcus faecium was later isolated and interpreted as a secondary pathogen. The patient was treated with intravenous meropenem and daptomycin, followed by intrathecal gentamicin, with consolidation to intravenous linezolid. After seven weeks of systemic therapy and two weeks of combined intrathecal treatment, CSF parameters normalized with simultaneous clinical improvement.
Conclusion: Capnocytophaga brain abscess can occur in immunocompetent hosts and may evade conventional microbiologic diagnostics. This case highlights the diagnostic and therapeutic challenges of culture-negative ventriculitis and underscores the value of molecular diagnostics in identifying oral-source polymicrobial anaerobic pathogens associated with complex Capnocytophaga brain abscess. In immunocompetent patients with coexisting periodontitis or recent dental procedures, early identification of Capnocytophaga may serve as a marker of a broader polymicrobial process and should prompt consideration of recurrent brain abscess and ventriculitis. Broad-range PCR sequencing represents a valuable adjunct in guiding targeted antimicrobial therapy when conventional diagnostics fail.
