Different brain effects during chronic and acute sacral neuromodulation in urge incontinent patients with implanted neurostimulators

OBJECTIVE: To compare changes in regional cerebral blood flow (rCBF), using positron emission tomography (PET), during chronic and acute sacral neuromodulation (SN). SN is an effective long-term treatment for chronic urge incontinence due to urinary bladder hyperactivity, as sensory nerves, spinal and supraspinal structures are probably responsible for the action of SN. It is not known which brain areas are involved, and the optimum benefit of SN is not immediate, suggesting that induced plasticity of the brain is necessary. PATIENTS AND METHODS: Brain activity was measured in two groups: 12 urge incontinent patients (11 women and one man; mean age 52 years) in whom an implanted unilateral S3 nerve neurostimulator had been effective for >6 months (mean time after implantation 4.5 years); and eight urge incontinent patients (seven women and one man; mean age 49 years) in whom the neurostimulator was activated for the first time in the PET scanner. RESULTS: During SN in chronically implanted patients, there were significant decreases in rCBF in the middle part of the cingulate gyrus, the ventromedial orbitofrontal cortex, midbrain and adjacent midline thalamus, and rCBF increases in the dorsolateral prefrontal cortex. During acute SN in newly implanted patients, there were significant decreases in rCBF the medial cerebellum, and increases in the right postcentral gyrus cortex, the right insular cortex and the ventromedial orbitofrontal cortex. Group analysis between chronic and newly implanted patients showed significant differences in the associative sensory cortex, premotor cortex and the cerebellum, all three involved in learning behaviour. CONCLUSIONS: These findings suggests that chronic SN influences, presumably via the spinal cord, brain areas previously implicated in detrusor hyperactivity, awareness of bladder filling, the urge to void and the timing of micturition. Furthermore, SN affects areas involved in alertness and awareness. Acute SN modulates predominantly areas involved in sensorimotor learning, which might become less active during the course of chronic SN.