Abstract
Background: Central neuropathic pain represents one of the most common symptoms in multiple sclerosis (MS) and it seriously affects quality of life. Spinal mechanisms may contribute to the pathogenesis of neuropathic pain in MS. Converging evidence from animal models and neurophysiological and clinical studies in humans suggests a potential effect of transcranial direct current stimulation (tc-DCS) on neuropathic pain. Spinal application of DCS, i.e., transcutaneous spinal DCS (ts-DCS), may modulate nociception through inhibition of spinal reflexes. Therefore, ts-DCS could represents an effective, safe and well-tolerated treatment for neuropathic pain in MS, a largely unexplored topic. This study is a pilot randomized double-blind sham-controlled trial to evaluate the efficacy of ts-DCS on central neuropathic pain in MS patients.Methods: Thirty-three MS patients with central neuropathic pain were enrolled and randomly assigned to two groups in a double-blind sham-controlled design: anodal ts-DCS group (n = 19, 10 daily 20-min sessions, 2 mA) or sham ts-DCS group (n = 14, 10 daily 20-min sessions, 0 mA). The following clinical outcomes were evaluated before ts-DCS treatment (T0), after 10 days of treatment (T1) and 1 month after the end of treatment (T2): neuropathic pain symptoms inventory (NPSI), Ashworth Scale (AS) for spasticity and Fatigue Severity Scale (FSS). A subgroup of patients treated with anodal ts-DCS (n = 12) and sham ts-DCS (n = 11) also underwent a parallel neurophysiological study of the nociceptive withdrawal reflex (NWR) and the NWR temporal summation threshold (TST), two objective markers of pain processing at spinal level.Results: Anodal ts-DCS group showed a significant improvement in NPSI at T1, which persisted at T2, while we did not detect any significant change in AS and FSS. Sham ts-DCS group did not show any significant change in clinical scales. We observed a non-significant trend towards an inhibition of NWR responses in the anodal ts-DCS group at T1 and T2 when compared to baseline.Conclusions: Anodal ts-DCS seems to have an early and persisting (i.e., 1 month after treatment) clinical efficacy on central neuropathic pain in MS patients, probably through modulation of spinal nociception.Clinical Trial Registration: www.ClinicalTrials.gov, identifier #NCT02331654.
Highlights
Pain represents one of the most disabling symptoms of multiple sclerosis (MS), in that it adversely affects most aspects of healthrelated quality of life and is often neglected and undertreated
In the active transcutaneous spinal DCS (ts-DCS) group, we found a significant reduction in Neuropathic Pain Symptoms Inventory (NPSI) mean values (F(2,17) = 5.175; p = 0.013) at both T1 (Bonferroni’s corrected paired t-test: p = 0.023) and T2 (p = 0.008) when compared to T0 (Table 2; Figure 1)
The intergroup analysis showed a significant improvement in the NPSI score in the active ts-DCS group compared to the sham ts-DCS group at both T1 (F(1,31) 4.194; p = 0.049) and T2 (F(1,31) 6.637; p = 0.015; Figure 1)
Summary
Pain represents one of the most disabling symptoms of multiple sclerosis (MS), in that it adversely affects most aspects of healthrelated quality of life and is often neglected and undertreated. Central neuropathic extremity pain is described as a continuous burning, tingling or aching pain, unilateral or bilateral in distribution, affecting legs and feet, even in the early stages of the disease This type of pain is thought to be caused by lesions in brain and spinal cord nociceptive pathways leading to a dysregulation in inhibitory and/or excitatory pain mechanisms, including GABA-ergic interneurons and NMDA receptors (Olechowski et al, 2013). This type of MS-related pain has a prevalence ranging from 16 to 26% (Foley et al, 2013; Solaro et al, 2018) and its treatment remains a significant challenge as available therapies are scarcely effective or poorly tolerated (O’Connor et al, 2008; Paolucci et al, 2016). This study is a pilot randomized double-blind sham-controlled trial to evaluate the efficacy of ts-DCS on central neuropathic pain in MS patients
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