Restoration of mammillothalamic functional connectivity through thiamine replacement therapy in Wernicke's encephalopathy

Resting-state functional MRI (fMRI) is now providing further understanding of neuropsychiatric illnesses. However, its practical applicability in the clinical realms is still questionable. Here we report three consecutive followed-up resting-state fMRI data in a single case with Wernicke encephalopathy before and after high-dose thiamine replacement therapy ranging over 20 months. We measured the mammillothalamic functional connectivity strength between the first ROI (mammillary body) and a voxel which showed the highest co-activation among voxels within the anterior thalamus (the second ROI) to enhance the specificity of the functional connectivity data. We found that the time-series changes in the mammillothalamic functional connectivity generally paralleled to the changes in delayed verbal and nonverbal recall memory scores in the left and right hemisphere, respectively. Among these, the left-side connectivity and delayed verbal recall score seemed to be related to the overall clinical status change. Modified directed transfer function (dDTF) analysis also identified significant information flows with mammillary-to-thalamic direction except at the acute illness state. Our findings, though preliminary in nature, suggest the practical applicability of resting-state fMRI to trace an effect of thiamine replacement therapy on the memory tract function in Wernicke encephalopathy at single-patient level.