A case study of midbrain abscess by Aggregatibacter aphrophilus in an immunocompetent adult

Background : Aggregatibacter aphrophilus, a commensal oropharyngeal coccobacillus and a member of the HACEK group (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella ) of bacteria, is known to occasionally cause brain abscesses in immunosuppressed individuals and endocarditis in children with known congenital heart conditions. Brainstem abscesses in immunocompetent adult hosts are not routinely reported. The rarity of such abscesses and their tendency to mimic a number of neurological conditions like brainstem stroke symptoms, Miller-Fisher syndrome and metastases further delays diagnosis and often leads to more complications due to the delay in treatment. Case Presentation : We present a case of a 66-year-old, relatively healthy male, presenting with progressively worsening diplopia, ptosis and anisocoria with a recent history of a dental procedure. Initial symptoms were akin to a midbrain stroke but imaging revealed a serpentine ring enhancing brainstem lesion with significant edema, not respecting any vascular distribution, extending from the thalamus to the upper pons. This additionally posed significant challenges to obtain samples for microbiological testing given the location of the lesion and the potential of a lumbar puncture causing a herniation. After stroke was completely ruled out with extensive imaging, samples of the mass were obtained with the help of aspiration from an external ventricular drain and an organism was isolated. The patient, who was initiated on empiric antibiotics early in his hospital course improved slowly with narrower spectrum antibiotics. Resolution of the lesion was confirmed with repeat imaging on post-admission clinic visits. Conclusion : This case highlights the challenges in diagnosis and need for increased vigilance about the possibility of Aggregatibacter aphrophilus-related brain and brainstem abscess after periodontal infections in immunocompetent individuals that can often present with rapid clinical deterioration. Early diagnosis and appropriate antimicrobial therapy are crucial for recovery