Comparing cortico-motor hotspot identification methods in the lower extremities post-stroke: MEP amplitude vs. latency.

Transcranial magnetic stimulation (TMS) is a technique used to probe and measure cortico-motor responses of the nervous system. However, lower extremity (LE) specific methodology has been slow to develop. In this retrospective analysis, we investigated what motor evoked potential metric, amplitude (MEPamp) or latency (MEPlat), best distinguished the motor-cortical target, i.e. hotspot, of the tibialis anterior and soleus post-stroke. Twenty-three participants with stroke were included in this investigation. Neuronavigation was used to map hotspots, derived via MEPamp and MEPlat, over a 3cm × 5cm grid. Distances between points with the greatest response within a session and between days were compared. Both criterion, amplitude and latency, provided poor identification of locations between trials within a session, and between multiple visits. Identified hotspots were similar only 15 % and 8% of the time between two assessments within the same session, for amplitude and latency respectively. However, MEPamp was more consistent in identifying hotspots, evidenced by locations being less spatially distant from each other (Amplitude: 1.4 cm (SD 0.10) Latency: 1.7 (SD 1.04), P = 0.008) within a session and between days (Amplitude: 1.3 cm (SD 0.95), Latency 1.9 cm (SD 1.14), P = 0.004). While more work is needed to develop LE specific methodology for TMS, especially as it applies to investigating gait impairments, MEPamp appears to be a more consistent criterion for hotspot identification when compared to MEPlat. It is recommended that future works continue to use MEPamp when identifying tibialis anterior and soleus hotspots using neuronavigation.

Glucose uptake of the spinal cord in patients with multiple sclerosis detected by ¹8F-fluorodeoxyglucose PET/CT after walking.

STUDY DESIGN: Case report. OBJECTIVES: To determine [(18)F]-fluorodeoxyglucose ([(18)F]-FDG) uptake in the spinal cord of patients with multiple sclerosis (MS) was compared with healthy controls after treadmill walking. SETTING: Colorado Translational Research Imaging Center, University of Colorado School of Medicine, Aurora, CO, USA. METHODS: Eight mildly disabled patients with MS and eight healthy subjects performed 15 min of treadmill walking at a self-selected pace. Two minutes after walking began, each participant was injected with ≈8 mCi of [(18)F]-FDG into a catheter inserted into an antecubital vein. Immediately after walking positron emission tomography/computed tomography (PET/CT) imaging was performed on each participant. Images were analyzed to determine [(18)F]-FDG uptake within the spinal cord. RESULTS: Total spinal cord [(18)F]-FDG uptake was lower in patients with MS (1.48±0.36 and 1.55±0.33, P=0.04), specifically within the thoracic (1.32±0.27 and 1.41±0.24, P<0.01) and the lumbar (1.58±0.40 and 1.89±0.43, P=0.04) spinal cord regions. CONCLUSION: This is the first report of [(18)F]-FDG uptake in the spinal cord of patients with MS. The decreased [(18)F]-FDG uptake within the thoracic and lumbar spinal cord regions could be associated with autonomic nervous system and walking/motor dysfunctions that are often seen in patients with MS. PET/CT imaging with [(18)F]-FDG is highly useful for the demonstration of impaired glucose metabolism in the spinal cord of patients with MS.

Asymmetric glucose uptake in leg muscles of patients with Multiple Sclerosis during walking detected by [18F]-FDG PET/CT.

BACKGROUND: In patients with Multiple Sclerosis (MS), comparative leg muscle strength asymmetries are common and typically accompanied by walking difficulties. Underlying mechanisms for these asymmetries are not completely known, but altered muscle energetics may play a role. OBJECTIVE: To investigate glucose uptake asymmetries in leg muscles of patients with mild MS during walking. METHODS: Eight MS and 8 healthy control (CON) participants performed a 15-min treadmill walking test at self-selected speed. They were injected with a glucose tracer (18F-FDG) two minutes into the test and immediately upon completion, underwent Positron Emission Tomography/Computed Tomography (PET/CT) imaging. RESULTS: MS group walked at a lower speed than the healthy control group (P < 0.01), however it was found that: 1) ([18F]-FDG) uptake in knee and hip flexors was higher compared to the CON group (P = 0.02); 2) the MS group exhibited asymmetrical strength of the knee flexors (P = 0.03); 3) [18F]-FDG uptake was significantly lower in the weaker knee flexors of patients with MS (P < 0.01). CONCLUSIONS: [18F]-FDG uptake and strength asymmetries in the legs of patients with MS indicate greater metabolic costs during activity, which may play a major role in premature muscle fatigability and subsequent impaired walking capacity.