title: Association of anxiety with intracortical inhibition and descending pain modulation in chronic myofascial pain syndrome.
abstract: BACKGROUND
  This study aimed to answer three questions related to chronic myofascial pain syndrome (MPS): 1) Is the motor cortex excitability, as assessed by transcranial magnetic stimulation parameters (TMS), related to state-trait anxiety? 2) Does anxiety modulate corticospinal excitability changes after evoked pain by Quantitative Sensory Testing (QST)? 3) Does the state-trait anxiety predict the response to pain evoked by QST if simultaneously receiving a heterotopic stimulus [Conditional Pain Modulation (CPM)]? We included females with chronic MPS (n = 47) and healthy controls (n = 11), aged 19 to 65 years. Motor cortex excitability was assessed by TMS, and anxiety was assessed based on the State-Trait Anxiety Inventory. The disability related to pain (DRP) was assessed by the Profile of Chronic Pain scale for the Brazilian population (B:PCP:S), and the psychophysical pain measurements were measured by the QST and CPM.
  
  
  RESULTS
  In patients, trait-anxiety was positively correlated to intracortical facilitation (ICF) at baseline and after QST evoked pain (β = 0.05 and β = 0.04, respectively) and negatively correlated to the cortical silent period (CSP) (β = -1.17 and β = -1.23, respectively) (P <0.05 for all comparisons). After QST evoked pain, the DRP was positively correlated to ICF (β = 0.02) (P < 0.05). Pain scores during CPM were positively correlated with trait-anxiety when it was concurrently with high DRP (β = 0.39; P = 0.02). Controls' cortical excitability remained unchanged after QST.
  
  
  CONCLUSIONS
  These findings suggest that, in chronic MPS, the imbalance between excitatory and inhibitory descending systems of the corticospinal tract is associated with higher trait-anxiety concurrent with higher DRP.
authors.forename: Liliane Pinto
authors.initials: LP
authors.lastname: Vidor
authors.affiliation: Post-Graduate Program in Medical Sciences, School of Medicine, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil. iracitorres@gmail.com.
authors.forename: Iraci L S
authors.initials: IL
authors.lastname: Torres
authors.forename: Liciane Fernandes
authors.initials: LF
authors.lastname: Medeiros
authors.forename: Jairo Alberto
authors.initials: JA
authors.lastname: Dussán-Sarria
authors.forename: Letizzia
authors.initials: L
authors.lastname: Dall'agnol
authors.forename: Alicia
authors.initials: A
authors.lastname: Deitos
authors.forename: Aline
authors.initials: A
authors.lastname: Brietzke
authors.forename: Gabriela
authors.initials: G
authors.lastname: Laste
authors.forename: Joanna R
authors.initials: JR
authors.lastname: Rozisky
authors.forename: Felipe
authors.initials: F
authors.lastname: Fregni
authors.forename: Wolnei
authors.initials: W
authors.lastname: Caumo
mesh_terms: D000328:Adult; D000368:Aged; D058443:Catastrophization / Q000503:physiopathology*; D002540:Cerebral Cortex / Q000503:physiopathology*; D059350:Chronic Pain / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009209:Myofascial Pain Syndromes / Q000503:physiopathology*; D009433:Neural Inhibition; D017288:Pain Threshold; D050781:Transcranial Magnetic Stimulation