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A 71 year old man was transferred to our hospital with a two week history of gait disturbance and disorientation. He had no apparent history of malnutrition, surgery of digestive tract, or alcoholism. Eye movements were limited vertically. Deep tendon reflexes were absent in the lower limbs. Vibration sensation was absent at ankles. His score on the Mini Mental State Examination was 14. Diffusion weighted magnetic resonance imaging (DW-MRI) revealed hyperintense lesions in periaqueductal region of the midbrain and medial thalami (fig 1(A)). Signal of these regions was also intensified on T2 weighted imaging (fig 1 (B)), but less markedly.
The MRI findings in Wernicke's encephalopathy in the acute phase reportedly include hyperintense areas around the third ventricle and aqueduct on T2 weighted and FLAIR imaging.1,2 Characteristic topographical distribution of abnormal signal intensity on DW imaging in the setting of disorientation and polyneuropathy suggested that our patient had Wernicke's encephalopathy. Plasma vitamin B1 level was later revealed to be reduced to 8 μg/ml (20 to 50 μg/ml).
The diagnosis of Wernicke's encephalopathy can be difficult in the absence of apparent history of chronic alcohol intake or malnutrition. Detection of reduced plasma thiamine level may be crucial, however, it takes time to obtain the value. Magnetic resonance imaging is convenient measure to detect the characteristic topographic distribution. Of particular interest, our patient showed the hyperintense on DW imaging in these locations. Because the apparent diffusion coefficient of the lesion is not reduced as was reported by Oka et al,3 the hyperintense appears to be derived from T2 shine through effect and may represent vasogenic oedema. Diffusion weighted magnetic resonance imaging can be obtained sooner than T2 weighted or FLAIR imaging. Thus, we emphasise that DW-MRI is superior to conventional MRI in depicting the lesion of acute Wernicke's encephalopathy, which enables early diagnosis of the disease.
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