ABSTRACT
Clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) has been recently proposed as a clinical-radiological syndrome. Several causes of MERS have been reported including infectious diseases. We present herein on a case of MERS induced by dengue fever in a Japanese traveler. A 48-year-old male returning from Thailand and Cambodia was admitted for an unknown fever. Following admission, the dengue virus was diagnosed with a positive RT-PCR result. On day 5 of the illness, regardless of reduced fever, weakness suddenly developed in both upper limbs. A cerebral MRI showed hyperintensities in the splenium of the corpus callosum on T2-weighted and diffusion-weighted images. The symptoms resolved completely within two days of onset. The patient was diagnosed as having MERS due to the MRI features and the mild clinical course. Although only a few cases of MERS caused by dengue fever have been reported, the condition is possibly underdiagnosed. It is hypothesized that dengue fever can induce MERS as dengue fever can cause increased endothelium permeability and hypo-sodium which have been proposed in the pathogenesis of MERS. However, there is currently limited evidence for this. Further research is recommended to demonstrate a causal association between dengue fever and MERS.