Abstracts

Interictal psychosis can be observed in about 4-10% of patients with epilepsy and is more commonly associated with temporal lobe epilepsy (TLE). Pathophysiological mechansisms of interictal psychosis are poorly understood. We aimed to examine neuropathological abnormalities in vivo in patients with interictal psychosis using Magnetization Transfer Imaging (MTI), a technique known to be more sensitive than conventional MRI in detecting subtle neuropathological changes. MTI was performed in 20 TLE patients and interictal psychosis with either unilateral hippocampal sclerosis (HS [ndash] left HS: 6; right HS: 4) or no focal lesions on conventional MRI (normal MRI [ndash] 10 patients). Twenty age- matched patients without psychosis (6 left HS, 4 right HS, 10 normal MRI) were investigated for comparisons. Magnetization Transfer Ratio (MTR) maps were created for each subject. These maps were then stereotactically normalised using a MTR template and compared as groups using SPM 2. In addition, each subject was tested neuropsychologically and test-scores were used for correlational analysis with MTR maps. Group analysis of the MTR maps revealed no significant differences comparing psychotic and non psychotic patients. We found significant reductions of MTR in the left middle temporal gyrus when comparing psychotic and non-psychotic patients with normal MRI. These abnormalities could not be attributed to volume reductions.Neuropsychological testing revealed significant differences in executive functions and semantic memory functions between the psychotic and the non psychotic patient groups. Correlation of test-scores with MTR in the psychotic group showed decreases of MTR in the left temporal lobe correlating with semantic memory functions. Our findings suggest that there may be subtle neuropathological abnormalities in the left temporal cortex of patients with interictal psychosis that are undetectable on conventional MRI. These abnormalities appear to be functionally relevant as they are associated with impaired semantic memory functions (Supported by National Lottery, National Society for Epilepsy)