Maria da Graça Lopes Tarragó

Motor Cortex Excitability and BDNF Levels in Chronic Musculoskeletal Pain According to Structural Pathology.

The central sensitization syndrome (CSS) encompasses disorders with overlapping symptoms in a structural pathology spectrum ranging from persistent nociception [e.g., osteoarthritis (OA)] to an absence of tissue injuries such as the one presented in fibromyalgia (FM) and myofascial pain syndrome (MPS). First, we hypothesized that these syndromes present differences in their cortical excitability parameters assessed by transcranial magnetic stimulation (TMS), namely motor evoked potential (MEP), cortical silent period (CSP), short intracortical inhibition (SICI) and short intracortical facilitation (SICF). Second, considering that the presence of tissue injury could be detected by serum neurotrophins, we hypothesized that the spectrum of structural pathology (i.e., from persistent nociception like in OA, to the absence of tissue injury like in FM and MPS), could be detected by differential efficiency of their descending pain inhibitory system, as assessed by the conditioned pain modulation (CPM) paradigm. Third, we explored whether brain-derived neurotrophic factor (BDNF) had an influence on the relationship between motor cortex excitability and structural pathology. This cross-sectional study pooled baseline data from three randomized clinical trials. We included females (n = 114), aged 19–65 years old with disability by chronic pain syndromes (CPS): FM (n = 19), MPS (n = 54), OA (n = 27) and healthy subjects (n = 14). We assessed the serum BDNF, the motor cortex excitability by parameters the TMS measures and the change on numerical pain scale [NPS (0–10)] during CPM-task. The adjusted mean (SD) on the SICI observed in the absence of tissue injury was 56.36% lower than with persistent nociceptive input [0.31(0.18) vs. 0.55 (0.32)], respectively. The BDNF was inversely correlated with the SICI and with the change on NPS (0–10)during CPM-task. These findings suggest greater disinhibition in the motor cortex and the descending pain inhibitory system in FM and MPS than in OA and healthy subjects. Likewise, the inter-hemispheric disinhibition as well as the dysfunction in the descending pain modulatory system is higher in chronic pain without tissue injury compared to a structural lesion. In addition, they suggest that a greater level of serum BDNF may be involved in the processes that mediate the disinhibition of motor cortex excitability, as well as the function of descending inhibitory pain modulation system, independently of the physiopathology mechanism of musculoskeletal pain syndromes.

The Relationship Between Cortical Excitability and Pain Catastrophizing in Myofascial Pain

UNLABELLED Pain catastrophizing regularly occurs in chronic pain patients. It has been suggested that pain catastrophizing is a stable, person-based construct. These findings highlight the importance of investigating catastrophizing in conceptualizing specific approaches for pain management. One important area of investigation is the mechanism underlying pain catastrophizing. Therefore, this study explored the relationship between a neurophysiological marker of cortical excitability, as assessed by transcranial magnetic stimulation, and catastrophizing, as assessed by the Brazilian Portuguese Pain Catastrophizing Scale, in patients with chronic myofascial pain syndrome. The Pain Catastrophizing Scale is a robust questionnaire used to examine rumination, magnification and helplessness that are associated with the experience of pain. We include 24 women with myofascial pain syndrome. The Brazilian Portuguese Pain Catastrophizing Scale and cortical excitability were assessed. Functional and behavioral aspects of pain were evaluated with a version of the Profile of Chronic Pain scale and by multiple pain measurements (eg, pain intensity, pressure pain threshold, and other quantitative sensory measurements). Intracortical facilitation was found to be significantly associated with pain catastrophizing (β = .63, P = .001). Our results did not suggest that these findings were influenced by other factors, such as age or medication use. Furthermore, short intracortical inhibition showed a significant association with pressure pain threshold (β = .44, P = .04). This study elaborates on previous findings indicating a relationship between cortical excitability and catastrophizing. The present findings suggest that glutamatergic activity may be associated with mechanisms underlying pain catastrophizing; thus, the results highlight the need to further investigate the neurophysiological mechanisms associated with pain and catastrophizing. PERSPECTIVE This study highlights the relationship between cortical excitability and catastrophizing. Cortical measures may illuminate how catastrophizing responses may be related to neurophysiological mechanisms associated with chronic pain.

Clinical Value of Serum Neuroplasticity Mediators in Identifying the Central Sensitivity Syndrome in Patients With Chronic Pain With and Without Structural Pathology.

Background and Objectives:Central sensitivity syndrome (CSS) encompasses disorders with overlapping symptoms in a spectrum of structural pathology from persistent somatic nociception (eg, osteoarthritis) to absence of tissue injury such as in fibromyalgia, chronic tension-type headache, and myofascial pain syndrome. Likewise, the spectrum of the neuroplasticity mediators associated with CSS might present a pattern of clinical utility. Methods:We studied the brain-derived neurotrophic factor (BDNF), tumor necrosis factor-&agr; (TNF-&agr;), and interleukins 6 (IL-6) and IL-10 in female patients with CSS absent of structural pathology (chronic tension-type headache [n=30], myofascial pain syndrome [n=29], fibromyalgia [n=22]); with CSS due to persistent somatic/visceral nociception (osteoarthritis [n=27] and endometriosis [n=32]); and in pain-free controls (n=37). Results:Patients with CSS absent of structural pathology presented higher serum TNF-&agr; (28.61±12.74 pg/mL) and BDNF (49.87±31.86 ng/mL) than those with persistent somatic/visceral nociception (TNF-&agr;=17.35±7.38 pg/mL; BDNF=20.44±8.30 ng/mL) and controls (TNF-&agr;=21.41±5.74 pg/mL, BDNF=14.09±11.80 ng/mL). Moreover, CSS patients absent of structural pathology presented lower IL levels. Receiver operator characteristics analysis showed the ability of BDNF to screen CSS (irrespective of the presence of structural pathology) from controls (cutoff=13.31 ng/mL, area under the curve [AUC]=0.86, sensitivity=95.06%, specificity=56.76%); and its ability to identify persistent nociception in CSS patients when experiencing moderate-severe depressive symptoms (AUC=0.81; cutoff=42.83 ng/mL, sensitivity=56.80%, specificity=100%). When the level of pain measured on the visual analog scale was <5 and moderate-severe depressive symptoms were observed TNF-&agr; discriminated structural pathology in the chronic pain conditions (AUC=0.97; cutoff=22.11 pg/mL, sensitivity=90%, specificity=91.3%). Conclusion:Neuroplasticity mediators could play a role as screening tools for pain clinicians, and as validation of the complex and diffuse symptoms of these patients.

Descending Control of Nociceptive Processing in Knee Osteoarthritis Is Associated With Intracortical Disinhibition: An Exploratory Study.

AbstractBased on the hypothesis that an imbalance in excitatory and inhibitory input is a central mechanism of knee osteoarthritis chronic pain (KOACP), this exploratory study had the following aims: to compare whether the function of the descending inhibitory pain pathway is associated with the state of inhibition in the corticospinal system indexed by the motor-evoked potential (MEP) and the cortical salient period (CSP) in patients with severe osteoarthritis (OA) and healthy controls; and to determine if there is correlation between the measures of intracortical inhibition (CSP, MEP) with changes on the numerical pain scale (NPS [0–10]) in KOACP during a conditioned pain modulation (CPM)-task considering the effect of self-reported function assessed by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and analgesic use.In a cross-sectional study, we included females (n = 21), with disability by pain or stiffness due to KOACP and healthy controls (n = 10), aged 19 to 75 years. The motor cortex excitability parameters (MEP and CSP) were assessed using the transcranial magnetic stimulation. We assessed the pain and disability by the WOMAC, and change on NPS (0–10) during CPM-task.A Multivariate analysis of covariance revealed that the adjusted mean (SD) on the MEP amplitude was 13.53% higher in the OA than in healthy subjects (1.33 [0.49] vs 1.15 [0.13]), respectively (P = 0.16). The adjusted mean (SD) on the CSP observed in OA patients was 23.43% lower than in healthy subjects (54.54 [16.10] vs 70.94 [22.87]), respectively (P = 0.01). The function of the descending pain modulatory system assessed by change on NPS (0–10) during a CPM-task was negatively correlated with the cortical excitability parameter indexed by the CSP (P = 0.001). Also, the CSP was negatively correlated with the pain and disability assessed by the WOMAC index.These findings support the hypothesis that the change in cortical plasticity in KOACP is associated with less intracortical inhibition, as measured by the CSP. These results show that the neural change in the motor cortex in KOACP is associated with pain and disability levels, and also with decreased activation of the endogenous pain-modulating system by a CPM-task.