Abstracts

Limbic encephalitis is an autoimmune disorder characterised by onset after the 20th year of age, seizures of temporal semiology, and/or a charactheristic mesiotemporal neuropsychological deficit or psychiatric symptoms. Both paraneoplastic (sometimes associated to onconeuronal antibodies) or non-paraneoplastic (most commonly associated to Voltage-Gated Potassium-Channel Antibodies or antithyroideal antibodies) cases are described. MRI usually shows signal increase and sometimes minor swelling on anterior mesiotemporal structures. We conducted a VBM analysis to look for objective grey matter (GM) changes, and confirm its extension or limitation to the limbic structures., 8 consecutive in-patients fulfilled the criteria for the syndromal diagnosis. Standard brain MRIs of the patients were either normal or showed some swelling in the amygdala or hippocampus, but in no case the signs of hippocampal sclerosis was found. Patients who fulfilled the diagnosis criteria but had large lesions that could interfere with the VBM analysis were not recruited. A 3 Tesla 3D-T1 image was obtained on all patients, and processed using SPM5 (www.fil.ion.ac.uk). 73 normal subjects were used as control group. Final normalised and modulated-GM images were smoothed with a 10 mm isotropic gausssian kernel. A two-group t-test was used for the analysis, with age, gender and total brain volume as corregressors. Results were corrected for multiple comparisons using a false discovery rate approach (p=0.01), as no a priori assumption of expecting results in any region was made., The patient group showed a statistically significant greater GM-concentration bilaterally in the anterior mesiolimbic structures, especially on the right side, as compared to controls. Lowering the extend threshold down to 0 would not bring additional extralimbic clusters. There were no voxels showing higher GM concentration on the control group., VBM is a fully-automated objective test to detect structural differences. In this subgroup of patients, bilateral limbic system abnormalites, especially of the most ventral structure, the amygdala, were observed. It also showed how specifically affected is the limbic system, for there is only significant findings in those structures. An automated analysis using VBM can also be applied to individual cases and can help on the diagnosis of patients with seemingly normal MRI.
Acknowledgement: The authors would like to thank Prof. Angela Vincent, Oxford, for performing the VGKC antibody radioimmunoprecipitation assay.[figure1],