An autopsy case of granulomatous amebic encephalitis caused by Balamuthia mandrillaris involving prior amebic dermatitis

Abstract

An 82-year-old man, who was healthy and had worked as a farmer, experienced worsening neurological symptoms over a seven-month period, which eventually caused his death. Multiple fluctuating brain lesions were detected radiographically. Clinically, sarcoidosis was ranked high among the differential diagnoses because of the presence of skin lesions showing granulomatous inflammation, confirmed by biopsy. The patient's cerebrospinal fluid was also examined, but no definitive diagnosis was made while he was alive. An autopsy revealed multiple granulomatous amebic encephalitis lesions in the brain. Genetic and immunohistochemical analyses identified Balamuthia (B.) mandrillaris, a free-living ameba, which resides in soil and fresh water, as the causative organism. A retrospective examination revealed B. mandrillaris in the biopsied skin as well as cerebrospinal fluid, strongly suggesting that the ameba had spread into the brain percutaneously. Few studies have detailed the cutaneous pathology of B. mandrillaris infections. In general, granulomatous amebic encephalitis is extremely difficult to diagnose without autopsy, but the present case provides a clue that could allow similar cases to be diagnosed earlier; that is, the presence of skin lesions.

Keywords: Balamuthia mandrillaris; amebic dermatitis; autopsy; free-living ameba; granulomatous amebic encephalitis.

Fig 1

MRI findings of the brain. (A) A T1‐weighted image taken 69 days before death exhibits gadolinium‐enhanced lesions with broad perifocal edema in the right thalamus and frontal cortex. (B, C) T1‐weighted images taken 51 (B) and 29 (C) days before death display that both the lesions are shrinking despite not being treated. (D) On diffusion‐weighted images taken 30 days before death, new lesions are emerging throughout the CNS. They are not enhanced by contrast medium and, hence, are considered to be ischemic lesions. (E) Diffusion‐weighted images taken four days before death depict the lesions gradually increased in number. They tend to be distributed in areas in contact with CSF, such as the ventricular wall and subarachnoid space.

Fig 2

Cytological features of CSF aspirated during the patient's clinical course, on Papanicolaou staining. The sample is cellular and contains a variety of inflammatory cells, such as lymphocytes, macrophages, and plasma cells. Inset shows an ameba noticed during a retrospective review. Scale bar: 20 μm.

Fig 3

Gross (A), histological (B‐E), and immunohistochemical (F) features of the skin lesions. (A) An erythematous nodule, measuring approximately 2 cm in diameter, is observed on the skin of the right upper arm shown. (B) A a low magnification of the biopsied skin, multinodular inflammatory lesions are found in the dermis and subcutaneous tissue. (C) The predominant cellular components are lymphocytes, plasma cells, and macrophages, whereas a limited number of multinucleated giant cells (arrow) are scattered within and around the inflammatory foci. No necrosis is observed. The diagnosis at the time of the biopsy is granulomatous inflammation. (D) On a retrospective examination, unfamiliar, somewhat large cells with characteristic nuclear features are embedded in the inflamed foci, indicative of amebic trophozoites (depicted by circles). (E) At a higher magnification, each ameba has an oval nucleus and a distinct nucleolus, surrounded by relatively clear, occasionally vacuolated, amorphous cytoplasm (upper right). Some of the cell bodies of the amebae are narrow (upper middle). Most amebae are distributed separately, but sometimes two or more are found together (upper right). Some amebae with two nucleoli (lower left) or unclear nucleoli (lower middle) are also observed. An ameba engulfed by a macrophage is also found (lower right). (F) Immunohistochemistry with the antiserum against B. mandrillaris identifies immunoreactive organisms, indicative of the parasite infection. Scale bars: 20 μm.

Fig 4

Macroscopic findings of coronal slices of the autopsied brain. There are many dark red spotty lesions, indicating hemorrhagic or necrosis, on the cut surface. As pointed out on MRI, lesions are common in areas in contact with the ventricular wall or the brain surface. At autopsy, the choroid plexuses in the lateral ventricles are found to be severely affected. The lesion in the right thalamus (arrow), as detected at an earlier stage on MRI, is mostly necrotic and looks like a less active, obsolete lesion. Scale bar: 2 cm.

Fig 5

Histological findings of the autopsied brain. (A) Amebae are readily found in a smaller brain lesion. The amebae tend to reside around blood vessels and invade or compress the walls of the blood vessels, possibly responsible for bleeding and circulatory disorders. (B) A cyst of ameba with a prominent thick shell, is shown. (C) The antiserum against B. mandrillaris clearly immunolabels the amebae within the brain lesions. Scale bars: 20 μm.

Fig 6

Results of PCR targeting the mitochondrial 16S rRNA gene locus of B. mandrillaris. Amplicons are detected at a predicted size of 178 bp on lanes 1‐3 but not lane 4. M, marker; 1, positive control (cultured B. mandrillaris used to produce the antiserum); 2, brain lesion sample obtained at autopsy from the present case; 3, skin lesion sample obtained at by biopsy from the present case; 4, negative control (human brain sample obtained at biopsy from a case unaffected with amebae).