A Surviving Case of Acanthamoeba Granulomatous Amebic Encephalitis in a Hematopoietic Stem Cell Transplant Recipient

Abstract

BACKGROUND Acanthamoeba are free-living amoebae with potential to infect immunocompromised hosts. The mortality rate of granulomatous amebic encephalitis (GAE) due to Acanthamoeba exceeds 90% and there are currently no reports of survival of this infection in recipients of hematopoietic stem cell transplant. CASE REPORT We report herein the case of a 32-year-old man presenting to our service with abrupt neurological deterioration and seizures 5 months after allogeneic stem cell transplantation for Hodgkin lymphoma. Clinical and imaging findings were non-specific at presentation. Multiple circumscribed, heterogenous, mass-like lesions were identified on MRI. Brain biopsy was performed and revealed multiple cysts and trophozoites suggesting a diagnosis of granulomatous amebic encephalitis. PCR testing confirmed Acanthamoeba. Treatment with miltefosine, metronidazole, azithromycin, fluconazole, pentamidine isethionate, and co-trimoxazole was instituted and the patient survived and shows continued improvement with intensive rehabilitation. CONCLUSIONS We report the first successful outcome in this setting. The diagnosis would have been missed on cerebrospinal fluid analysis alone, but was rapidly made by histological analysis of brain biopsy. This diagnostically challenging infection is likely under-recognized. Early brain biopsy and commencement of a prolonged miltefosine-containing anti-ameba regimen can be curative.

Figure 1.

Imaging studies. (A) FLAIR images at presentation. Note circumscribed heterogenous 4-cm mass-like lesion in the left occipital lobe (arrows). Note also a 15-mm lesion with similar single characteristics within the medial right frontal lobe (arrow). Further areas of edema are present in the splenium of the corpus callosum and temporal lobe on the left, which correlate with the patient’s alexia without agraphia and right superior quadrantanopia, respectively. FLAIR images are shown. T1, T2, diffusion, and contrast-enhanced imaging modes revealed partial restricted diffusion and enhancement, but these abnormalities are more marked on FLAIR images. (B) FLAIR images following biopsy. Ten days later, there was significant deterioration with extension of the edema into the left temporal lobe and a mild mass effect (arrows). A more circumscribed focus of high signal intensity within the center of the lesion represents hematoma following biopsy. The right frontal lesion is unchanged. (C) FLAIR images at day 140. Follow-up scan 5 months later demonstrates resolution of the edema on the left, with significant dilatation of the posterior horn of the left lateral ventricle, consistent with ex-vacuo dilatation (asterisks). The high signal intensity within the left temporal lobe, which continues around the dilated posterior horn, is well-demarcated and is consistent with gliosis (arrows).

Figure 2.

Histopathology. (A) Low-power magnification H&E photomicrographs of brain histology. Fragments of grey and white matter showing perivascular and parenchymal chronic inflammation, composed of lymphocytes, macrophages, and microglial cells. Rare multinucleated giant cells are seen (H&E ×10 objective). (B) Low-power magnification H&E photomicrographs of brain histology. Several variably sized aggregates of microglial cells forming microglial nodules are seen (H&E ×10 objective). (C) High-power magnification H&E photomicrographs of brain histology. Multiple rounded organisms are seen. The majority have a well-defined capsule with abundant granular/vacuolated cytoplasm, a round nucleus, and prominent central karyosome, consistent with amoebic trophozoites (blue arrows). Smaller ones have dark nuclei with a wrinkled and rather refractile outer capsule, consistent with amoebic cysts (red arrows) (H&E ×40 objective).