Tandem deep brain stimulation--challenging new structural targets for Parkinson's disease

Deep brain stimulation (DBS) targets for Parkinson's disease have been limited to neuronal regions wherein lesions have produced beneficial effects. Improvements in imaging allow placement in small and novel targets. Additionally, due to the ability of impulse generators to accommodate multiple electrodes, simultaneous stimulation in multiple neuronal regions is possible. Given that the two most disabling clinical features of Parkinson's disease, namely postural instability and dementia, have evaded effective treatment, consideration for new structural targets is warranted. Characteristics of dementia in parkinsonism include progressive deficits in attention and executive function. Additionally, many patients experience pronounced variability in cognition with profound fluctuations/variability in attention and alertness. Anecdotal and initial trial reports concerning DBS to the fornix/hypothalamus have been associated with improvement in memory function and reductions in expected cognitive decline in patients with early Alzheimer's disease. The fornix constitutes the major inflow and output pathway from the hippocampus and medial temporal lobe. I hypothesize that tandem DBS, targeting the STN/GPi and fornix/hypothalamus and/or hippocampus may have a positive impact on improving cognitive function and/or reducing risk for subsequent dementia with Lewy bodies/Parkinson dementia. Such targets also pose potential negative ramifications. Nevertheless, given the tremendous disability produced by dementia, new structural targets require systematic study.