Abstract
Common symptoms of multiple sclerosis (MS) include motor impairments of the lower extremities, particularly gait disturbances. Loss of balance and muscle weakness, representing some peripheral effects, have been shown to influence these symptoms, however, the individual role of cortical and subcortical structures in the central nervous system is still to be understood. Assessing [18F]fluorodeoxyglucose (FDG) uptake in the CNS can assess brain activity and is directly associated with regional neuronal activity. One potential modality to increase cortical excitability and improve motor function in patients with MS (PwMS) is transcranial direct current stimulation (tDCS). However, tDCS group outcomes may not mirror individual subject responses, which impedes our knowledge of the pathophysiology and management of diseases like MS. Three PwMS randomly received both 3 mA tDCS and SHAM targeting the motor cortex (M1) that controls the more-affected leg for 20 min on separate days before walking on a treadmill. The radiotracer, FDG, was injected at minute two of the 20 min walk and the subjects underwent a Positron emission tomography (PET) scan immediately after the task. Differences in relative regional metabolism of areas under the tDCS anode and the basal ganglia were calculated and investigated. The results indicated diverse and individualized responses in regions under the anode and consistent increases in some basal ganglia areas (e.g., caudate nucleus). Thus, anodal tDCS targeting the M1 that controls the more-affected leg of PwMS might be capable of affecting remote subcortical regions and modulating the activity (motor, cognitive, and behavioral functions) of the circuitry connected to these regions.
Highlights
Positron emission tomography (PET) imaging with the glucose analog [18F]fluorodeoxyglucose (FDG) can effectively measure cerebral glucose uptake and metabolism (Rudroff et al, 2020)
Subject 1 had been diagnosed with multiple sclerosis (MS) for 12 years, reported a score of 0 on the Patient Determined Disease Scale (PDDS), a score of 1.78 on the Fatigue Severity Scale (FSS), and was not physically active according to the stated guidelines
The rt caudate nucleus displayed an 8.68% increase, the lt substantia nigra, rt putamen, and lt putamen all had >4% increase in activity, and the rt substantia nigra was the only area that showed a decrease in activity (−7.38%) in active compared to SHAM (Table 1 and Figure 2). This case report indicated that transcranial direct current stimulation (tDCS) over the left M1 was capable of affecting remote, subcortical regions, like the caudate nucleus, in patients with MS (PwMS) during walking
Summary
Positron emission tomography (PET) imaging with the glucose analog [18F]fluorodeoxyglucose (FDG) can effectively measure cerebral glucose (the primary substrate used for ATP genesis) uptake and metabolism (Rudroff et al, 2020). The tracer can be injected during a relevant activity and the resulting distribution of FDG can be measured after a known temporal delay. Using this methodology, FDG-PET images can represent a “brain metabolic signature” associated with physical performances (Rudroff et al, 2020). Applying FDG-PET at rest, Roelcke et al (1997) and Bakshi et al (1998) found reduced glucose metabolism within the brain of patients with MS (PwMS). The results of Kindred et al (2015) suggested a decoupling of brain glucose utilization and motor task performance
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