Neuroschistosomiasis, cerebellar acute schistosomal encephalopathy infected by Schistosoma japonicum
Further questioning disclosed that the patient was a native, while he has moved to Jinmen City, a highly endemic area for S japonicum (1), over 6 years ago. A flood, caused by the extraordinary rainstorm on July 19th 2016, hit the current residence of the patient. The embankment overflowed with water, the houses and fields were flooded.
Schistosomiasis (bilharzia), a helminthic infection caused by blood flukes (trematode worms) of the genus Schistosoma, is prevalent in tropical and subtropical areas (2). Three major species, including Schistosoma mansoni, Schistosoma haematobium and Schistosoma japonicum, are known to cause severe disease in humans. S japonicum is primarily distributed in China, Indonesia, the Philippines. S haematobium and S mansoni have a wider spread involving Africa and the Middle East, whereas only S mansoni is present in the Americas (3).
Neuroschistosomiasis, referring to schistosome involvement of the central nervous system (CNS), is a granulomatous host immune response induced by schistosome eggs. Neuroschistosomiasis is rare, even in the endemic areas. S mansoni and S haematobium usually affect the spinal cord, whereas S japonicum causes mostly encephalic disease. Neurological forms of neuroschistosomiasis consist of acute schistosomal encephalopathy (ASE) and pseudotumoral encephalic schistosomiasis (PES). S japonicum is the most frequent cause of ASE, which are more common in travellers or immigrants to schistosome-endemic regions who are exposed to schistosome antigens for the first time. PES occurs most frequently in people from endemic areas without any other symptoms of schistosomiasis. On CT and MRI, ASE shows edema and multifocal, small, contrast-enhanced lesions in the frontal, parietal, occipital lobes and brainstem; PES shows a tumor-like lesion surrounded by edema, associated with mass effect and heterogeneous contrast enhancement. The cerebrospinal fluid can be normal non-specific findings. The eosinophil count in blood is usually very high, but can be normal. Eggs in stool samples or urine may not be detected. Because ASE usually develops in non-immune people, antibody detection in serum samples is useful for ASE (4).
On histology, neuroschistosomiasis are characterized by inflammations of the giant cell and epithelioid cell granulomas with a necrotic center containing the eggs and an outer layer of plasma cells, eosinophils, and fibroblasts. Although the degenerating eggs may crenate and distort, making species classification difficult, the characteristics of the well-preserved eggs are identified by microscopy. The shell of eggs is brown in color with a slight birefringent, compared to that in paragonimiasis eggs, which mimic schistosome eggs and are capable of involving the CNS, with a bright birefringent. Among the three species of Schistosoma, S haematobium and S mansoni are similar in size, whereas the former with a terminal spine and the latter with a lateral spine; S japonicum is the smallest and has no really visible spine. In addition, Ziehl-Neelsen staining is helpful for differentiating the fresh eggs: S mansoni and S japonicum shells retain carbol fuchsin, while those of S haematobium do not (5, 6).
In our opinion, the patient should be considered as a non-immune people, who migrated from non-endemic area to endemic area (1); the flood, containing the infected waters, might increase the risks of exposure. Although no eggs were detected in the stool-samples, serological examination for S japonicum was positive after the operation. The patient was treated with praziquantel, remaining well at follow up.
Contributed by Dai-Zhong Wang, Li Yao, Tao Zhang, Tie-Yan Wang, Rui-Juan Zhu, Xue-Qiang Chen, Xian-Bin Tang