Brain stimulation | 2019
Transcranial direct current stimulation (tDCS) for the treatment of a Multiple Sclerosis symptom cluster
Abstract
People with Multiple Sclerosis (PwMS) have an over five-fold increased risk of experiencing and being treated for neuropathic pain. Interestingly, pain has been described as a potentially moderating factor of fatigue and depression [1]. Up to 92% of PwMS are affected by fatigue [2] and 24% suffer from depression [3]. Depressed PwMS aremore likely to have pain and there is a positive association between the interference of painful symptoms, and pain severity, with depression severity [4]. Pain, fatigue, and depression are interdependently associated and potentially modifiable [5]. Thus, improving pain symptoms may improve fatigue and depression, which would contribute to an improved quality of life. Conceptually, the study of this MS symptom cluster (pain, fatigue, depression) recognizes that symptoms occur concurrently and that co-occurring symptoms may provide an efficient target for assessment and management. The question at hand is what is the best treatment for this MS symptom cluster? One possible modality is transcranial direct current stimulation (tDCS). To date, no study has investigated the effects of tDCS to improve this MS symptom cluster. We conducted a double blind, sham-controlled, and randomized crossover pilot study. Six moderately disabled PwMS (relapsingremitting MS; 3 female; age 1⁄4 46.7 ± 14.1 yrs.) completed two randomly ordered blocks of stimulation (tDCS or sham). Each block involved five daily sessions. At the first visit, participants completed the, Fatigue Severity Scale (FSS), visual analog scale for pain (VAS), and Beck Depression Inventory (BDI) questionnaires. Isokinetic leg strength and fatigue testing were also performed. Leg strength was determined via five sets of one isokinetic maximal flexion and extension (60 /s) and objectively defined the more-affected leg. A tDCS device (Soterix Medical Inc., New York, NY) delivered a small direct current through two surface sponge electrodes (5 cm 7 cm, soaked with 15 mM NaCL). The anode was placed over the M1 representation of the more-affected leg and the cathode was placed over the contralateral supraorbit. The isokinetic fatigue test (FT) involved 40 continuous maximal contractions (concentric/concentric, 120 /s) of the knee extensors and flexors. The FT was performed using the weaker (more-affected) leg. The peak work of each repetitionwas used to calculate the fatigue index (FI-W) as follows: (total work performed in the last half/total work performed in the first half) * 100. The stimulation blocks (tDCS or sham) were performed in a randomized order. For tDCS, the participants received 2 mA of stimulation for 20 min while seated comfortably and quietly. The intensity started at 0 mA and incrementally increased to 2mA. At minute 20, the current was gradually reduced