Assessment of blood-brain barrier penetration of miltefosine used to treat a fatal case of granulomatous amebic encephalitis possibly caused by an unusual Balamuthia mandrillaris strain

Abstract

Balamuthia mandrillaris, a free-living ameba, causes rare but frequently fatal granulomatous amebic encephalitis (GAE). Few patients have survived after receiving experimental drug combinations, with or without brain lesion excisions. Some GAE survivors have been treated with a multi-drug regimen including miltefosine, an investigational anti-leishmanial agent with in vitro amebacidal activity. Miltefosine dosing for GAE has been based on leishmaniasis dosing because no data exist in humans concerning its pharmacologic distribution in the central nervous system. We describe results of limited cerebrospinal fluid (CSF) and serum drug level testing performed during clinical management of a child with fatal GAE who was treated with a multiple drug regimen including miltefosine. Brain biopsy specimens, CSF, and sera were tested for B. mandrillaris using multiple techniques, including culture, real-time polymerase chain reaction, immunohistochemical techniques, and serology. CSF and serum miltefosine levels were determined using a liquid chromatography method coupled to tandem mass spectrometry. The CSF miltefosine concentration on hospital admission day 12 was 0.4 μg/mL. The serum miltefosine concentration on day 37, about 80 h post-miltefosine treatment, was 15.3 μg/mL. These are the first results confirming some blood-brain barrier penetration by miltefosine in a human, although with low-level CSF accumulation. Further evaluation of brain parenchyma penetration is required to determine optimal miltefosine dosing for Balamuthia GAE, balanced with the drug's toxicity profile. Additionally, the Balamuthia isolate was evaluated by real-time polymerase chain reaction (PCR), demonstrating genetic variability in 18S ribosomal RNA (18S rRNA) sequences and possibly signaling the first identification of multiple Balamuthia strains with varying pathogenicities.

Keywords: Balamuthia; Encephalitis; Granulomatous; Miltefosine.

Fig. 1

Magnetic resonance imaging (MRI) of the brain during the patient’s clinical course. (a). Initial MRI on admission Day 1 revealed a nonspecific multifocal lesion involving the left frontal temporal lobe with surrounding edema and midline shift. (b). MRI on Day 8 revealed postoperative changes with diminished mass effect and midline shift. (c). MRI on Day 20 (flair axial image) revealed a new lesion in left temporo-occipital white matter (arrow) and further reduction in edema with resolution of midline shift. (d). MRI on Day 26 (T1 sagittal image) revealed numerous new foci throughout the brain (arrows)

Fig. 2

Variable positions in the 18S rRNA gene sequences from Balamuthia mandrillaris isolates available in GenBank as of 2013. The alignment was made with ClustalW using Geneious v7.1.5. A dash (-) indicate an insertion/deletion. Total length of alignment was 1,973 base pairs. The isolate from the patient described in this report was designated as CDC:V630

Fig. 3

Hematoxylin and eosin (H&E) or indirect immunofluorescence (IFA) staining of tissue sections. (a) A section of brain stained with H&E—Balamuthia amebae are seen interspersed within the tissue at magnification X 100. (b) A similar section of brain reacted with anti-Balamuthia mandrillaris serum in the IFA test at magnification X 100. (c) IFA reactivity of Balamuthia amebae in a section of lung at magnification X 100 indicating dissemination of amebae into the lung. (d) A high power (magnification X 1,000) view of an ameba in the lung by IFA staining