Overactive Bladder (OAB) is associated with elevated urgency and urinary incontinence. These lower urinary tract symptoms (LUTS) seems to be paralleled by structural white matter (WM) hypointensities in the brain [1]. 
We aimed to investigate the role of global and local WM tract function in women with OAB using traditional and novel structural imaging markers.

13 female OAB patients (37.3±8.6 years) and eighteen healthy female controls (HC, 32.6±9.5 years) were included in this study. All participants were assed using the female LUTS (FLUTS) questionnaire. Diffusion Tensor Imaging (DTI) was recorded on a 3-Tesla Philips Ingenia scanner. To analyze DTI data in a voxel-wise fashion, Tract-Based Spatial Statistics (TBSS) was used to minimize multi-subject registration errors (FSL, http://www.fmrib.ox.ac.uk/fsl). The four primary quantitative DTI measures, fractional anisotropy (FA), mean (MD), axial (AD), and radial diffusivity (RD) as well as fiber density (FD, a novel non-tensor-derived diffusion marker) are then derived voxel-wise. Correlations with urological scores within the OAB group were only explored in regions with significant differences from HC. Statistical analysis, comparing OAB to HC, was performed using FSL randomise tool and results were corrected for multiple comparisons (p<0.05) [2].

Using a whole brain (voxel-to-voxel) approach, FA (Fig. 1) and FD (Fig. 2) was reduced in patients with OAB compared to HC in the corpus callosum (genu and splenium), corona radiata (anterior and posterior), and superior longitudinal fasciculus (SLF). Using a tract-based approach, we found lower FD in the left thalamic radiation, corpus callosum forceps minor, inferior fronto-occipital fasciculus, inferior longitudinal fasciculus (ILF), SLF, and arcuate fasciculus. 

OAB patients showed a positive correlation between “Female LUTS” scores and FD (all p < 0.019, r = 0.64-0.67) of the left ILF, SLF and arcuate fasciculus as well as between the “LUTS Quality of life” scores and FA in corpus callosum forceps major and FD of the left arcuate fasciculus, ILF, and SLF (all p < 0.044, r = 0.61-0.81).

Our results demonstrate regional and global WM alterations in patients with OAB, as seen by lacking commissure pathways connecting bilateral frontal and thalamic regions as well as parietal and premotor cortex..
Using FD, we claim that OAB patients showed an altered fiber weighting in certain intra-axonal compartments such as SLF and ILF, i.e. in important associations fibers regulating attention, motor behavior and memory processing.
The positive correlation of FA and LUTS scores could index an overuse of particular WM regions, which do normally show higher values in HC (as sign of intact neuronal integrity).

We conclude that the described  white matter alterations in OAB patients contribute to their deminished capability of LUT control. These neuroimaging findings help to improve our understanding of OAB aetiology and the involved supraspinal attribute.

Tadic SD, Griffiths D, Murrin A, Schaefer W, Aizenstein HJ, Resnick NM. Brain activity during bladder filling is related to white matter structural changes in older women with urinary incontinence. Neuroimage. 2010 Jul 15;51(4):1294-302.
Smith SM, Nichols TE. Threshold-free cluster enhancement: addressing problems of smoothing, threshold dependence and localisation in cluster inference. Neuroimage. 2009 Jan 1;44(1):83-98.