Automatic Detection of Brain Abnormalities of the Medial Temporal Lobe(s) Suggestive of Autoimmune Limbic Encephalitis

Rationale:Diagnostic criteria for possible or definite autoimmune limbic encefalitis include brain abnormalities of the medial temporal lobe(s) in MRI's (Lancet Neurol. 2016 Apr;15(4):391–404). Although some objective measures to identify those abnormalities, i.e. swelling of amygdala/hippocampus or increased signal in the fluid attenuated inversion recovery (FLAIR) scans are reported (e.g. Epilepsia. 2013 Sep;54(9):1679-87), a visual inspection of the MRI is still clinical standard. In this research, a open and free to download software is developed (analyseMRI), for autonomous and complete objective volumetric and intensity analysis of the hippocampus, amygdala and cerebral cortex simultaneously.Methods:Based on the FreeSurfer package (http://surfer.nmr.mgh.harvard.edu) a freeware software has been developed using Matlab (http://mathworks.com) to analyse segmented 3D T1-weighted and coregisterd 3D FLAIR series. From the masked structural scan, after specifying the isotropic voxel dimension, the volume of the structure is determined. From the masked FLAIR scan a voxel intensity analysis is performed. First, the intensities are normalized. From here, statistical information such as intensity mean, mode, variance and standard deviation are reported. For universality, also the relative volumes and intensity parameters are determined, relative to the corresponding hemisphere’s cerebral white matter parameter. A limbic encephalitis suspicion is formed as follows: presence of significant volumetric increase in combination with hyperintensity indicated the onset of limbic encephalitis, a following significant volumetric decrease indicates atrophy.From 20 healthy controls a scans were taken previously. The software compares the patient’s parameters to this control average and reports the comparison results. Additionally, if a patient’s volume deviates at least two standard deviations from the control average, this is reported as a significant volume deviation. Next, the software reports the absolute volumes of the structures. Finally, the software checks whether there is clear one-sided hyperintensity in the hippocampi of amygdalae, by comparing the relative intensity mode and standard deviations. A one-sided hyperintensity is characterized by an increased relative intensity mode and simultaneously decreased intensity standard deviation on a structure, compared to the other hemisphere’s corresponding structure.Results:In general, (relative) volumetric increases combined with hyperintensity of the hippocampi and amygdalae, as well as volumetric decreases of the cerebral cortex as a whole, were detected in 5 patients diagnosed with definite limbic encephalitis. In addition, 21 potential limbic encephalitis patients were analyzed. Significant volumetric deviations were found in 48%, one-sided hyperintensities in the FLAIR-signal were found in 76%.Conclusions:To objectify inspection of T1-weighted and FLAIR MRI scans in patients with potential autoimmune limbic encephalitis, a software (analyseMRI) was developed to yield a fast, automatic analysis of MRI scans. As a result, this software produces per patient a waring for a suspicion of limbic encephalitis