(624) A Case of Midbrain Abscess by Aggregatibacter aphrophilus in an Immunocompetent Adult

Introduction: Aggregatibacter aphrophilus (A. aphrophilus) formerly called Haemophilus aphrophilus, belongs to the HACEK group. This oropharyngeal commensal microbe can cause infective endocarditis and brain abscesses, that can be present in immunocompromised patients, and in congenital heart disease. [1] [2]
A Danish study showed that bacteria from oral cavity were less likely to form deep brain abscesses. [3] Our case, in contrast, shows that deep A. aphrophilus brain abscess can form.

Description: A 66-year-old right-handed Caucasian male with cardiovascular history presented with sudden onset diplopia and left blurry vision, after dental abscess drainage 3 weeks ago. Brain imaging and ophthalmology exam was normal in the ED.
Exam showed left cranial nerve III palsy with anisocoria. MRI with contrast revealed ring enhancing midbrain-thalamic lesion with vasogenic edema (Figure 1 and 2). Post admission day 4, clinical deterioration with worsening mentation led to intubation, ventriculostomy, continuation of Acyclovir, Ceftriaxone and Vancomycin). Cerebrospinal fluid (CSF) was normal.
As microbiologic cultures were negative, lesion fluid aspiration was done neurosurgically, showing pus, that grew Gram-negative bacilli isolated as Aggregatibacter aphrophilus. Antibiotics were changed to Ceftriaxone and Metronidazole with improvement by day 7. Imaging revealed no additional abscesses or infective endocarditis. Post admission day 35 MRI showed significant abscess resolution.

Discussion: A. aphrophilus can cause brainstem abscess, after periodontal infections with rapid clinical deterioration. Early diagnosis and appropriate antimicrobial therapy are crucial for recovery. Molecular techniques are needed to identify A. aphrophilus. Further studies are needed to understand predisposing factors for A. aphrophilus brainstem abscess in immunocompetent adults.