A 16-year-old boy from Orissa with complaints of non-pulsatile, holocranial headache and low-grade, intermittent evening rise of temperature for 3 months and was on anti-tubercular therapy with steroids and anti-edema measures for clinically suspected central nervous system tuberculosis. He reported transient improvement of constitutional symptoms over the next 15 days, following which he developed right hemiparesis, motor aphasia and altered sensorium and was referred to our hospital. There was no preceding history of seizures, myoclonus, history of dog bite or vaccination. No history of exposure to unsafe sexual practices or drug abuse. There was no recent history of travel or water related activities preceding this illness.
On admission, he was febrile, drowsy and unresponsive to commands. Neurological examination revealed neck rigidity, right-sided hemiplegia, with hypertonia, and bilateral extensor plantar responses. Routine investigations including serum biochemistry (liver and renal function tests) and hemogram were normal except for mild peripheral blood leukocytosis (total white blood cells count was 12,600/cubic milimeter with neutrophillic predominance). Serology for HIV, and venereal disease research laboratory test was non-reactive.
A cranial magnetic resonance imaging (MRI) [Figure 1] revealed multiple, coalescing, predominantly T1 and T2 hypointense lesions with ring enhancement located in left capsuloganglionic region, thalamus, brainstem and cortico-medullary junctions, also lesions involving left basal ganglia showed a characteristic peripheral thin rim of T1 hyperintensity with blooming on gradient-sequences and hyperdensity on plain-computed tomography (CT) scans indicative of bleed. Magnetic resonance spectroscopy (MRS) [Figure 2] from the lesions revealed elevated lactate and choline peaks. Fluid attenuated inversion recovery images sequences revealed sulcal hyperintensities with contrast enhancement, suggestive of leptomeningitis. The left caudate head and lentiform nuclei showed features suggestive of acute infarct, corresponding to recurrent artery of Huebner territory.
Based on MRI features, possibility of a hemorrhagic meningoencephalitis either of viral or fungal origin was suspected. He succumbed to his illness on the second day of admission. A complete autopsy was performed following informed consent from close relatives of the deceased. At autopsy, the brain was diffusely edematous and revealed large necrotizing lesions with yellowish center surrounded by zones of hemorrhage involving parietooccipital lobes bilaterally, left orbitofrontal and inferior occipital regions [Figure 3]. On coronal slicing, multiple hemorrhagic, necrotic lesions were seen along the cortical ribbon mostly located in the crown of gyrus/depth of sulcus in left middle and inferior frontal lobe. At the level of optic chiasm, the left insular cortex showed large nodular confluent coalescing necrotic lesion [Figure 3] with central zones of yellowish xanthomatous areas with peripheral rim of hemorrhage [Figure 3a], extending along the sylvian fissure following the gyral pattern and superiorly into the left putamen compressing the ipsilateral ventricle. The surrounding white matter was edematous. Distinct pale necrotic lesions were seen in the left head of caudate, left uncus, left anterior hippocampus and anterior thalamic nucleus. The cingulate gyrus on the right also showed a hemorrhagic lesion involving the cortical ribbon.
The brainstem showed a nodular, hemorrhagic, necrotic circumscribed lesion in the upper pons on left side. No lesions were seen in mid-brain or cerebellum. Histologically these lesions revealed florid meningoencephalitis with mixed infiltrate of lymphocytes and histiocytes flooding the subarachnoid space. The larger leptomeningeal vessels were thrombosed with dense inflammation [Figure 3b]. The inflammatory infiltrates were seen invading the underlying cortex. The smaller parenchymal venules entrapped in the inflammation were ruptured forming small pools of fresh hemorrhage. Parenchymal necrosis and hemorrhage was prominent with venulitis. Foci showed ill-formed granulomas with histiocytic aggregates and multinucleate giant cells. Special stains for fungal hyphae and acid fast bacilli were negative. Periodic acid Schiff stain highlighted several large trohphozoite form of amoeba surrounding penetrating venules and filling the Virchow Robin spaces in continuity with subarachnoid space [Figure 3c]. In addition scattered cysts morphologically resembling Acanthamoeba were detected perivascularly by silver stains [Figure 3d]. The trophozoites were large (25 microns to 40 microns), with thick cell wall and prominent nucleoli. The cysts were multinucleate with thick cell walls. Trophozoites and cysts were also found in necrotizing lesions in pons. The posterior half of eye ball with optic nerves removed at autopsy revealed dense inflammation expanding the subarachnoid space surrounding the optic nerve, particularly on the left side with scattered trophozoites detectable in the perioptic space and within the substance of the optic nerve.
The lungs were boggy, subcrepitant and revealed bilateral consolidation with evidence of bronchopneumonia on histology. No trophozoites were detectable. The liver and spleen were enlarged and revealed multiple small abscesses and necrotizing granulomas with scattered trophozoite forms of acanthamoeba. Cysts were not detectable in the organs. Dot polymerase chain reaction for acanthamoeba was positive in serum and in vitreous of the left eye and brain tissue [Figure 4] but negative in Cerebro spinal fluid. Dot blot is the simplification of conventional method, a mixture containing the molecule to be detected is applied directly on a membrane as a dot and is then spotted through circulate templates on to the membrane. No electrophoresis is applied and hence saves time, it confirms the presence of the biomolecules which can be detected by DNA probes or antibody. The principle is that a single oligoprobe can hybridize to a second DNA molecule that contains the target sequence. So, it is speculated that, following primary parasitemia secondary to poor host defenses, the parasite might have seeded the choroid of the left eye, spread through the lamina cribrosa into the peri-optic subarachnoid space, and extended along the subarachnoid space into basal cisterns, along sylvian fissure and into the parenchyma. We were handicapped with the absence of history and a very brief stay of the patient at our hospital, it is likely that he harboured the organism as a normal commensal probably in his nasal mucosa. Parasitemia would have occurred following breakdown of the local barriers secondary to viral infection.