Abstracts

Rationale: Hot water epilepsy (HWE) is a reflex epilepsy precipitated by hot water bath. While the semiology is similar to temporal complex partial seizures, with aura of fearfulness, dazed look with irrelevant speech, occasional visual and auditory hallucinations1, HWE is distinct in its evolution from reflex to spontaneous when left untreated. Hubs occupy a central position in networks and therefore are likely to help establish the crucial regions in the networks that differentiate the various pathological states. In this study, we attempt to unravel the pathological hubs defining reflex hot water epilepsy.  Methods: Ninety two patients with HWE (M: F:: 64: 28) and 60 age and gender matched healthy controls were recruited with the approval of institutional ethics committee. Fifty four patients had only reflex (R) seizures and 37 in addition had both reflex and spontaneous seizures (R+S). DTI (b value: 1000s/mm2, directions: 20) were obtained using 3.0 Tesla SIEMENS MAGNETOM Skyra MR™. Whole brain inter ROI tractography was calculated using AAL cortical atlas (N=90). The connectivity matrix was built using the number of tracts between ROIs. Betweenness centrality(BC), clustering coefficient (CC) and local efficiency (LE) were derived using Brain Connectivity Toolbox2. Hubs were defined as the top 20% of the nodes in the network that showed an increase in BC, decreased CC and increased LE in spontaneous compared to reflex. A Hierarchical Hub score was calculated based on the graph measure showing the abnormality3. An FDR corrected P value  < 0.05 was considered significant. Results: R+S group differed from R in sensory integration areas with a Hub score 3 in bilateral (BL) primary sensory areas, left (L) superior parietal lobule along with right (R) prefrontal areas, R insular region and R occipital regions. A hub score of 1 was noticed in peripheral areas of BL hippocampus-parahippocampus, R cingulum, R cuneus, precuneus R temporal lobe along with L precentral, caudate and pallidum, R thalamus, BL olfactory, the changes noted in the insula, cingulate, temporal and the hippocampal networks most associated with the clouding/loss of consciousness during hot water stimulation.  Conclusions: While involvement of temporal lobe seems to be a common network in both reflex and spontaneous HWE, the integration of parietal sensory networks with temporal lobe during a hot water bath is likely to be responsible for the reflex component of the seizures. Clouding/loss of consciousness in HWE, can be due to involvement of the lateral fronto-parietal networks and insula-cingular salience network.1Satishchandra, P. Hot-Water Epilepsy. Epilepsia (2003) 44, 29–32.2Rubinov, M. & Sporns, O. Complex network measures of brain connectivity: Uses and interpretations. NeuroImage (2010) 52, 1059–1069.3van den Heuvel, Martijn P., et al. "Aberrant frontal and temporal complex network structure in schizophrenia: a graph theoretical analysis." J Neurosci 30.47 (2010): 15915-15926. Funding: Nil