Study Design:
This is a single-center prospective, open-label, non-blinded, non-randomized, pilot study designed to evaluate the safety of deep brain stimulation (DBS) of the subgenual cingulate (SGC) in subjects diagnosed with apathetic behavioral variant frontotemporal dementia (abvFTD). In addition, the physiological and clinical effects of DBS will be assessed by neuroimaging and neuropsychological testing.
Investigators hypothesize that:
1. Bilateral subgenual cingulate deep brain stimulator implantation will be well-tolerated in apathetic behavioral variant frontotemporal dementia patients. In AIM 1 investigators will assess the safety of SGC DBS, by monitoring intraoperative and postoperative adverse events related to surgery and stimulation in abvFTD patients.
2. Bilateral subgenual cingulate deep brain stimulation will modulate brain circuits that are dysfunctional in patients with apathetic behavioral variant frontotemporal dementia. In AIM 2 investigators will determine the physiological impact and mechanisms of action of SGC DBS in abvFTD, by assessing cerebral metabolism with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET scans, functional connectivity with magnetoencephalography and resting state functional magnetic resonance imaging, cerebral atrophy with volumetric MRI, and plasma and cerebrospinal fluid biomarkers of neurodegeneration (glial fibrillar acidic protein and neurofilament light chain) and neuroinflammation (Olink inflammation panels I and II) in abvFTD patients.
3. Bilateral subgenual deep brain stimulation may improve some of the six core clinical features of behavioral variant frontotemporal dementia. In AIM 3 investigators will assess the clinical consequences of SGC DBS abvFTD, by performing the following neuropsychological tests: Neuropsychiatric index (NPI) and Apathy Evaluation Scale - Clinician version (AES-C) for apathy, NPI for disinhibition, compulsivity and hyperorality; Interpersonal reactivity index (IRI) for loss of empathy; National Institutes of Health - Executive Abilities: Measures and Instruments for Neurobehavioral Evaluation and Research (NIHEXAMINER) and Trail making test - A and B (TMT) for executive function; Social Cognition and Emotional Assessment (SEA)/Mini-SEA), and Frontotemporal lobar degeneration-modified Clinical Dementia Rating-I (FTLD CDR-I) for cognitive impairment.
Experimental Approach:
Investigators propose a 3-year open-label, single-arm, phase I study of subgenual cingulate deep brain stimulation for apathetic behavioral variant frontotemporal dementia. In years 1-2 investigators will screen frontotemporal dementia patients and enrol a total of 6 subjects who meet the study inclusion criteria. Prior to SGC DBS surgery, the subjects will undergo baseline neuroimaging (FDG PET, rsfMRI, MEG, vMRI and tractography), measurement of plasma and neuroinflammation (multiplex proximity extension assay (PEA) technology using Olink Explore Inflammation I and II panels), optional lumbar puncture (according to patient preference) for CSF biomarkers of neurodegeneration (GFAP) and NfL assays), and neuropsychological testing (NPI, AES-C, IRI, NIH-EXAMINER, TMT, SEA/mini-SEA and FTLD CDR-I). At 2 weeks after surgery, the DBS device will be turned on, with subsequent programming sessions at 4 weeks, 6 weeks, 8 weeks, 10 weeks, 3 months, 6 months, 9 months, 12 months and 24 months post-DBS surgery to optimize therapy. During programming, the DBS stimulation parameters will be titrated with the patient's apathy score, measured by AES-C, which is a validated 18-item apathy scale that can be easily administered in 10-20 minutes during the programming session. Full neuropsychological testing (NPI, AES-C, IRI, NIH-EXAMINER, TMT, SEA/mini-SEA and FTLD CDR-I ) will be performed at baseline before DBS surgery, and at 3-months, 6-months, 12-months and 24-months post-DBS surgery. Measurement of plasma neuroinflammatory biomarkers (Olink inflammation panels I and II) will be done at baseline before DBS surgery, and at 3-months, 6-months, 9-months, 12-months and 24-months post-DBS surgery. Lumbar puncture to obtain CSF for biomarkers of neurodegeneration (GFAP and NfL) will be optional and will be offered at baseline before DBS surgery and at 12-months and 24-months post-DBS surgery. Neuroimaging studies (FDG PET, rsfMRI, MEG, and vMRI) will be done at baseline before DBS surgery, and at 6-months, 12-months and 24-months post-DBS surgery. The baseline assessments and postoperative follow up will take place at Toronto Western Hospital. Investigators anticipate to complete patient follow-up by the end of year 3. However, it is possible that the 24-month follow up of a few patients may extend into year 4, depending on when their DBS surgery is performed.
