title: A Framework for Understanding the Relationship between Descending Pain Modulation, Motor Corticospinal, and Neuroplasticity Regulation Systems in Chronic Myofascial Pain.
abstract: Myofascial pain syndrome (MPS) is a leading cause of chronic musculoskeletal pain. However, its neurobiological mechanisms are not entirely elucidated. Given the complex interaction between the networks involved in pain process, our approach, to providing insights into the neural mechanisms of pain, was to investigate the relationship between neurophysiological, neurochemical and clinical outcomes such as corticospinal excitability. Recent evidence has demonstrated that three neural systems are affected in chronic pain: (i) motor corticospinal system; (ii) internal descending pain modulation system; and (iii) the system regulating neuroplasticity. In this cross-sectional study, we aimed to examine the relationship between these three central systems in patients with chronic MPS of whom do/do not respond to the Conditioned Pain Modulation Task (CPM-task). The CPM-task was to immerse her non-dominant hand in cold water (0-1°C) to produce a heterotopic nociceptive stimulus. Corticospinal excitability was the primary outcome; specifically, the motor evoked potential (MEP) and intracortical facilitation (ICF) as assessed by transcranial magnetic stimulation (TMS). Secondary outcomes were the cortical excitability parameters [current silent period (CSP) and short intracortical inhibition (SICI)], serum brain-derived neurotrophic factor (BDNF), heat pain threshold (HPT), and the disability related to pain (DRP). We included 33 women, (18-65 years old). The MANCOVA model using Bonferroni's Multiple Comparison Test revealed that non-responders (n = 10) compared to responders (n = 23) presented increased intracortical facilitation (ICF; mean ± SD) 1.43 (0.3) vs. 1.11 (0.12), greater motor-evoked potential amplitude (μV) 1.93 (0.54) vs. 1.40 (0.27), as well a higher serum BDNF (pg/Ml) 32.56 (9.95) vs. 25.59 (10.24), (P < 0.05 for all). Also, non-responders presented a higher level of DRP and decreased HPT (P < 0.05 for all). These findings suggest that the loss of net descending pain inhibition was associated with an increase in ICF, serum BDNF levels, and DRP. We propose a framework to explain the relationship and potential directionality of these factors. In this framework we hypothesize that increased central sensitization leads to a loss of descending pain inhibition that triggers compensatory mechanisms as shown by increased motor cortical excitability.
authors.affiliation: Post-Graduate Program in Medical Sciences, School of Medicine, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil; Pain and Palliative Care Service at Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil; Laboratory of Pain and Neuromodulation, Hospital de Clínicas de Porto AlegrePorto Alegre, Brazil.
authors.forename: Leonardo M
authors.initials: LM
authors.lastname: Botelho
authors.affiliation: Laboratory of Neuromodulation of Spaulding Rehabilitation of Harvard Medical School Boston, MA, USA.
authors.forename: Leon
authors.initials: L
authors.lastname: Morales-Quezada
authors.affiliation: Post-Graduate Program in Medical Sciences, School of Medicine, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil; Laboratory of Pain and Neuromodulation, Hospital de Clínicas de Porto AlegrePorto Alegre, Brazil.
authors.forename: Joanna R
authors.initials: JR
authors.lastname: Rozisky
authors.affiliation: Post-Graduate Program in Medical Sciences, School of Medicine, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil; Laboratory of Pain and Neuromodulation, Hospital de Clínicas de Porto AlegrePorto Alegre, Brazil.
authors.forename: Aline P
authors.initials: AP
authors.lastname: Brietzke
authors.affiliation: Post-Graduate Program in Medical Sciences, School of Medicine, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil; Pharmacology Department, Institute of Basic Health Sciences, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil.
authors.forename: Iraci L S
authors.initials: IL
authors.lastname: Torres
authors.affiliation: Post-Graduate Program in Medical Sciences, School of Medicine, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil; Laboratory of Pain and Neuromodulation, Hospital de Clínicas de Porto AlegrePorto Alegre, Brazil.
authors.forename: Alicia
authors.initials: A
authors.lastname: Deitos
authors.affiliation: Laboratory of Neuromodulation of Spaulding Rehabilitation of Harvard Medical SchoolBoston, MA, USA; Department of Physical Medicine and Rehabilitation, Harvard Medical SchoolBoston, MA, USA.
authors.forename: Felipe
authors.initials: F
authors.lastname: Fregni
authors.affiliation: Post-Graduate Program in Medical Sciences, School of Medicine, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil; Pain and Palliative Care Service at Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil; Laboratory of Pain and Neuromodulation, Hospital de Clínicas de Porto AlegrePorto Alegre, Brazil; Surgery Department, School of Medicine, Universidade Federal do Rio Grande do SulPorto Alegre, Brazil.
authors.forename: Wolnei
authors.initials: W
authors.lastname: Caumo
keywords: BNDF; CPM; MEP; QST; TMS; chronic pain; cortical excitability