Cortical Lesions in Patients With Multiple Sclerosis

Overview

Multiple sclerosis (MS) is an autoimmune disease, leading to inflammation and degeneration of neurons in the entire central nervous system (CNS). Not only does MS attack CNS white matter, the wiring of the brain, but it also affects so called grey matter, involved in communication between brain cells. Some studies have shown that grey matter damage and lesions to the outermost layer of the brain, the cortex, might serve as a better diagnostic and prognostic tool for MS patients. The issue is that cortical lesions only to a limited extent can be visualized by conventional magnetic resonance imaging (MRI) at 3 tesla. The new generation of ultra-high field MR scanners with a field strength of 7 tesla, has a higher sensitivity towards detecting these cortical lesions. We therefore wish to use the improved sensitivity of ultra-high field MRI to improve detection of cortical lesions, and to elucidate the detrimental effects of single lesions to the cortex, thereby improving both diagnosis and prognosis of the disease. By implementing newly developed ultra-high-resolution MR-sequences the amount and extent of cortical lesions to the area of the brain responsible of the sensory and motor function of the hand (sensorimotor hand area - SM1-HAND) will be investigated in patients with relapsing remitting and secondary progressive MS. We will also assess how these lesions affect manual dexterity and sensory function and how cortical lesions affect communication within brain areas. It is hypothesized that the amount and size of cortical lesions is highly involved in brain communication and manual function, a major problem in MS, and that this project will shed new light on how the disease damages this important brain area.

BACKGROUND. In recent years, several lines of research have shown that multiple sclerosis (MS) affects cortical grey matter and that the degree of cortical grey matter involvement is associated with cognitive and physical disability, but the specific impact of a cortical lesion on regional function remains to be clarified. High-field Magnetic Resonance Imaging (MRI) at 3T has been used to detect cortical lesions in MS, but histological examinations have shown that only 'the tip of the iceberg' is detected. Ultra-high field 7T MRI has a higher diagnostic sensitivity than 3T MRI. Although not every cortical lesion is detected even at 7T, a recent post-mortem verification study concluded that ultra-high field MRI "more than doubles detection of cortical MS lesions, compared to 3T MRI". Implementing 7T MRI in detection of cortical lesions and elucidating the behavioural and neurophysiological impact of cortical lesions is therefore a good candidate in aiding to resolve the clinico-radiological paradox reported in MS. AIMS and HYPOTHESES. This study is designed to clarify the occurence of cortical lesions within the primary sensory-motor hand area (SM1-HAND) and their impact on manual motor and sensory function, as well as regional cortical connectivity. The SM1-HAND is well suited to address this question, because functional integration in SM1-HAND can be studied in detail with transcranial magnetic stimulation (TMS) and high-resolution fMRI. Exploiting the increased sensitivity of 7T MRI to detect cortical lesions, the number, size and regional distribution of cortical lesions in SM1-HAND will be assessed and lesion load in SM1-HAND will be related to MRI-based, electrophysiological, and behavioral correlates of hand function. Specifically the following parameters will be assessed: 1. The extent that the primary sensorimotor cortex is affected by cortical lesions in patients with relapsing remitting and secondary progressive multiple sclerosis (MS). 2. The impact of a single cortical MS lesion in the sensorimotor cortex on upper extremity sensorimotor function. 3. The impact of a single cortical MS lesion in the sensorimotor cortex on regional intra-cortical connectivity. Hypotheses: 1\) The extent of cortical damage to the primary sensorimotor cortex is unknown, but based on clinical symptoms of motor function it is expected that up to 40% of patients show focal cortical lesions in this area and that this will include all subtypes of cortical lesions. 2a) It is hypothesized that unimanual motor function correlates negatively with the total cortical lesion load within the contralateral sensorimotor cortex, independent of age, gender, handedness, white matter lesion volume, axonal integrity of the cortico-spinal tract, central motor conduction time and cortical thickness of the sensorimotor cortex. 2b) It is hypothesized that the amount and size of cortical lesions within the primary sensorimotor cortex correlates positively with motor fatigue. 2c) It is hypothesized that unimanual sensory acuity correlates negatively with the total cortical lesion load within the contralateral sensorimotor cortex. 3a) It is expected cortical lesions to cause a shift in the digit representation, measured as the task related BOLD signal of the contralateral somatosensory cortex, away from the lesion. 3b) It is hypothesized that cortical lesions within the primary sensorimotor cortex affects the regional intra-cortical excitatory/inhibitory balance. 4\) It is further expected that the functional impact of regional cortical lesions are independent of age, gender, handedness, white matter lesion volume, axonal integrity of the cortico-spinal tract, central motor conduction time and cortical thickness of the sensorimotor cortex and scales with lesion type, number and volume. 3\. RESEARCH PLAN. Part 1. Whole-brain 7T MRI study to identify cortical lesions. Participants: The project is planned to involve 80 mildly to moderately affected patients (Expanded Disability Status Scale of \<5.5) with relapsing-remitting MS (RR-MS, n=40) or secondary progressive MS (SP-MS, n=40) who had no clinical relapse within the last three months and 20 healthy age-matched controls (age range: 18-70 years). Ultra-high field MRI. All participants will be studied with whole-brain ultra-high field MRI at 7T, using a research-only 7T Achieva MR system (Philips, Best, The Netherlands) located at Hvidovre Hospital. Whole-brain MR scanning will be performed with a dual transmit, 32-channel receive head coil (Nova Medical Products), including 3-dimensional (3-D), magnetization-prepared rapid acquisition of gradient echoes (MPRAGE) imaging at 0.65-mm isotropic resolution and 3-D, magnetization-prepared, fluid attenuated inversion recovery (MPFLAIR) imaging at 0.7-mm isotropic resolution (5). Whole-brain semi-quantitative (MP2RAGE), as well as a quantitative T2\* sequence will also be conducted. Additional examinations. Outside the MR scanner, physical impairment (EDSS), fatigue (Fatigue Scale for Motor and Cognitive Functions, FSMC), cognition (Symbol Digit Modalities Test, SMDT \& Paced Auditory Serial Addition Test, PASAT), depression (Beck Depression Inventory, BDI II) as well as sensorimotor hand function (9HPT, Jebsen Taylor Hand Function Test (JTT), Finger tapping, Grating Orientation Discrimination Test (GODT)) will be assessed. Part 2. Selected 7T MRI of the SM1-HAND. Participants: A sub-group of individuals who participated in part 1 will be asked to participate in part 2: It is expected that at least 20 patients will show at least one cortical lesion in the right or left SM1-HAND on 7T MRI. The lesion-positive patients (n\>20), an age- and EDSS- matched lesion-negative MS group (n\>20), and an age-matched healthy control group (n=20) will be studied. Recruitment will be done continuously to minimize the delay between part 1 \& 2. Participants will be scanned again with the 7T Achieva MR system using a reduced coronal field-of-view, covering the right and left SM1-HAND and the corticospinal tract. Structural imaging will include a 0.7 mm isotropic FLAIR sequence, and an ultra-high resolution MP2RAGE (0.5 mm isotropic) sequence as well as whole brain diffusion weighted imaging (DWI). Proton-Magnetic Resonance Spectroscopy (MRS) will be performed to measure regional N-acetyl-aspartate (NAA), GABA and glutamate concentration in right and left SM1-HAND. Lastly high-spatial resolution functional Blood Oxygen Level Dependent (BOLD) (fMRI) will be used to map the somatotopy of sensory and motor representations in SM1-HAND. Activation maps will be superimposed to individual lesion maps. TMS. The corticospinal conduction will be quantified with transcranial magnetic stimulation (TMS). A novel neuronavigated TMS mapping method developed by this group, which is sensitive to changes in cortico-motor representations of intrinsic hand muscles will also be implemented. Finally, aspects of intracortical inhibition in both SM1-HAND with established single-pulse and double-pulse TMS paradigms will be carried out. Conduction in the afferent somatosensory pathway will be assessed by recording somatosensory evoked potentials (SSEP).