Abstract
We recently reported on the efficacy of a personalized transcranial direct current stimulation (tDCS) treatment in reducing multiple sclerosis (MS) fatigue. The result supports the notion that interventions targeted at modifying abnormal excitability within the sensorimotor network could represent valid non-pharmacological treatments. The present work aimed at assessing whether the mentioned intervention also induces changes in the excitability of sensorimotor cortical areas. Two separate groups of fatigued MS patients were given a 5-day tDCS treatments targeting, respectively, the whole body somatosensory areas (S1wb) and the hand sensorimotor areas (SM1hand). The study had a double blind, sham-controlled, randomized, cross-over (Real vs. Sham) design. Before and after each treatment, we measured fatigue levels (by the modified fatigue impact scale, mFIS), motor evoked potentials (MEPs) in response to transcranial magnetic stimulation and somatosensory evoked potentials (SEPs) in response to median nerve stimulation. We took MEPs and SEPs as measures of the excitability of the primary motor area (M1) and the primary somatosensory area (S1), respectively. The Real S1wb treatment produced a 27% reduction of the mFIS baseline level, while the SM1hand treatment showed no difference between Real and Sham stimulations. M1 excitability increased on average 6% of the baseline in the S1wb group and 40% in the SM1hand group. Observed SEP changes were not significant and we found no association between M1 excitability changes and mFIS decrease. The tDCS treatment was more effective against MS fatigue when the electrode was focused on the bilateral whole body somatosensory area. Changes in S1 and M1 excitability did not correlate with symptoms amelioration. The neuromodulation treatment that proved effective against MS fatigue induced only minor variations of the motor cortex excitability, not enough to explain the beneficial effects of the intervention.
Highlights
Fatigue is defined as “a feeling of insufficient physical and/or mental energies interfering with the usual and desired activities” [1]
We identified the “hot-spot” of the right opponens pollicis (OP) muscle and the corresponding resting motor threshold (RMT) [27, 28]
Fatigue Levels Whole Body S1 Stimulation (S1wb) Analyses of variance indicated that modified fatigue impact scale (mFIS) changes were related to the type of stimulation (Real or Sham) when the bilateral personalized S1wb electrode was used [Stimulation × Treatment interaction F(1,8) = 9.692, p = 0.014, [6], Table 2]
Summary
Fatigue is defined as “a feeling of insufficient physical and/or mental energies interfering with the usual and desired activities” [1]. It is a common and highly disabling symptom in patients affected by multiple sclerosis (MS) even when other symptoms remain mild [2]. Involvement of the Motor Control System in MS Fatigue To date, there is no clear evidence pointing at a single factor causing MS fatigue and fatigue complaints appear completely unrelated to both clinical variables, such as type of MS, level of disability, or disease duration, and demographic ones, such as age, gender, and education level [3] Peripheral conditions, such as muscle weakness, may play a role, there are clear indications that much of MS fatigue has a central origin, most likely being the consequence of a failing central motor transmission to spinal alpha motor neurons [4]. We submitted the first subgroup to Cogiamanian’s same treatment only replacing the original mono-hemispheric with a bihemispheric stimulation (we will call this treatment SM1hand)
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