Objective:

To describe an unusual imaging presentation of Balamuthia mandrillaris granulomatous amebic encephalitis. 

Background:

Balamuthia mandrillaris is an ameba that can cause granulomatous amebic encephalitis in previously healthy patients. Prior cases have shown primarily lobar rim-enhancing lesions with later cerebellar involvement.  

Design/Methods:

N/A

Results:

A 58-year-old female presented with ten days of progressive right face and left hemibody numbness. Brain MRI showed a right pontine rim-enhancing lesion. Two weeks prior to presentation, patient developed skin abrasions that appeared uninfected and well-healed while gardening. CSF showed lymphocytic pleocytosis with unrevealing infectious, cytologic and rheumatologic workup. Neurologic exam over the following week progressed to include right internuclear ophthalmoplegia, right gaze palsy, worsening numbness and interval right sided facial droop and left arm and leg weakness. She was treated empirically with IV methylprednisolone, empiric antimicrobial coverage for TB, coccidioides, nocardiosis, and dermatitis molds. Interval MRIs showed increase in size of lesion with increased extent of vasogenic edema, involvement of the cerebral peduncles and areas of microhemorrhage later progressing to include new foci of rim-enhancement including cerebellar and cortical areas. Brain biopsy was nondiagnostic. She became comatose with loss of brainstem reflexes, was transitioned to comfort care and expired. Blood plasma microbial cell-free DNA sequencing later returned positive for Balamuthia mandrillaris, and preliminary CNS autopsy results were consistent with amebic organisms, pending CDC confirmation. 

Conclusions:

We describe a unique case of amebic granulomatous encephalitis, positive on metagenomic sequencing for Balamuthia madrillaris, with an initial rim-enhancing pontine lesion with quick progression to further brainstem, cerebellar, and later cortical and leptomeningeal involvement. This progression occured despite steroids and empiric typical antibiotic therapies, which made demyelinating, neoplastic, or typical infectious processes less likely. This case highlights the importance of consideration and early testing for this amebic etiology in atypical brainstem rim-enhancing lesions, as most Balamuthia diagnoses are made post-mortem.