Carpal tunnel syndrome: just a peripheral neuropathy?

Predictors of pain intensity in carpal tunnel syndrome: Development and validation of a model

OBJECTIVE

Pain often accompanies carpal tunnel syndrome and affects patients' health-related quality of life. The aim was to develop and validate a predictive model for the pain intensity of carpal tunnel syndrome using demographic, clinical, electrophysiological, and ultrasound findings.

METHODS

We conducted a secondary analysis of data from a large sample of patients (May 2017 to December 2022) with carpal tunnel syndrome. A total of 520 (53.0 %) mild, 276 (28.1 %) moderate, and 186 (18.9 %) severe syndromes were included in the complete data set of 982 hands (61.1 % female). The mean age was 57.8 (10.7) years and the median duration [interquartile range] of the symptoms was 4 [2,10] months. A regression model was developed and validated to predict pain intensity on a numerical rating scale using a tree-based machine learning algorithm.

RESULTS

The validation of the regression model showed good performance with a root mean squared error, R-squared, and mean absolute error of 1.35, 0.42, and 1.05, respectively. Overall, the top significant predictors of pain intensity were compound motor nerve action potential latency, nocturnal pain, and thenar weakness. These were followed by the cross-sectional area of the median nerve, sensory nerve action potential, bowing of the flexor retinaculum, disease duration, and body mass index. We did not find strong associations between the median nerve transcarpal latency, age, sex, and diabetes with the pain intensity of carpal tunnel syndrome.

CONCLUSION

Our model showed good performance in predicting the subjective pain intensity of carpal tunnel syndrome, even in the context of non-linear relations.

Psychological factors are associated with pain extent in patients with carpal tunnel syndrome

INTRODUCTION

Widespread pain may be related to psychosocial aspects in several musculoskeletal conditions, but the literature on carpal tunnel syndrome (CTS) is scarce.

OBJECTIVE

To determine the relationship between pain extent and psychological factors (catastrophizing, kinesiophobia, anxiety symptoms, and depression) in people with CTS.

METHODS

A cross-sectional study was conducted. The independent variables were: pain intensity, disability (QuickDASH), duration of symptoms, anxiety and depressive symptoms, catastrophizing, and kinesiophobia. The main outcome was: pain extent (% of total area and categories "pain within the median nerve-innervated territory" versus "extra-median nerve pain"). Correlation analysis was performed using Spearman's correlation coefficient. A linear regression model and binary logistic regression (both with forward selection) were performed to determine the main predictors of pain extent.

RESULTS

Forty-eight participants were included. A moderate positive correlation was found between catastrophizing (r = 0.455; p = 0.024) and disability (r = 0.448; p = 0.024) with total pain extent area. Regression models indicated that catastrophizing explained 22% of the variance in the pain extent (β = 0.003; 95% CI: 0.002-0.005), while kinesiophobia was the variable that best explained the distribution of pain in the extra-median territory (R2 Nagelkerke = 0.182). Null or weak correlations were found for the rest of the associations.

CONCLUSION

Catastrophizing and kinesiophobia were the main indicators of pain extent in people with CTS. Clinicians are advised to use specific questionnaires to check for the presence of catastrophizing or kinesiophobia in people with CTS and wider pain extension.

Central Sensitization in Patients with Chronic Pain Secondary to Carpal Tunnel Syndrome and Determinants

Purpose

Central sensitization (CS) is commonly seen in chronic pain disorders, including neuropathic pain. However, there exist inconsistencies concerning the presence of CS in chronic pain secondary to carpal tunnel syndrome (CTS). CS and neuropathic pain manifestations in CTS remain not well established. Therefore, this study aims to investigate the CS and pain profiles in patients with CTS and to explore the potential determinants associated with CS.

Patients and Methods

Patients with suspected CTS symptoms lasting 3 months or above and healthy controls were enrolled. History, physical examinations, and nerve conduction studies were employed to confirm the diagnosis and severity of median nerve dysfunction. The central sensitization inventory (CSI) was used to screen CS. Other outcomes included neuropathic pain, CTS-specific symptom severity and functions, emotion, and health-related quality of life. Between-group comparisons were conducted in terms of the CS presence. Logistic regression analysis was performed to identify determinants associated with CS.

Results

Over 60% of participants with CTS were found with clinical CS, significantly higher than that in the control group. More than 70% of the CTS participants were identified to have possible or very likely neuropathic pain components. In addition, one-fourth of CTS cases had depression or anxiety. Anxiety was associated with an increased risk of developing CS in CTS (adjusted OR=1.31, 95% CI 1.08-1.59), whereas higher self-perceived general health rating was negatively associated with the presence of CS (adjusted OR=0.92, 95% CI 0.88-0.97) in the multivariate adjusted regression model.

Conclusion

CS is prevalent in patients with CTS. Predominant neuropathic pain characteristics were uncovered in CTS patients as well as comorbid psychological distress. Significant association was found between anxiety and CS presence. Self-perceived general health was inversely related to CS. Further research is warranted to explore the mechanisms of anxiety and central pain processing in painful entrapment neuropathy.

Carpal Tunnel Syndrome: Neuropathic Pain Associated or Not with a Nociplastic Condition

Carpal tunnel syndrome (CTS) has been traditionally classified as primarily a neuropathic condition with or without pain. Precision medicine refers to an evidence-based method of grouping patients based on their susceptibility to biology, prognosis of a particular disease, or in their response to a specific treatment, and tailoring specific treatments accordingly. In 2021, the International Association for the Study of Pain (IASP) proposed a grading system for classifying patients into nociceptive, neuropathic, or nociplastic phenotypes. This position paper presents data supporting the possibility of subgrouping individuals with specific CTS related-pain into nociceptive, neuropathic, nociplastic or mixed-type phenotypes. Carpal tunnel syndrome is a neuropathic condition but can also be comorbid with a nociplastic pain condition. The presence of extra-median symptoms and the development of facilitated pain processing seem to be signs suggesting that specific CTS cases can be classified as the nociplastic pain phenotype. The clinical responses of therapeutic approaches for the management of CTS are inconclusive. Accordingly, the ability to identify the predominant pain phenotype in patients with CTS could likely be problematic for producing efficient treatment outcomes. In fact, the presence of a nociplastic or mixed-type pain phenotype would explain the lack of clinical effect of treatment interventions targeting the carpal tunnel area selectively. We propose a clinical decision tree by using the 2021 IASP classification criteria for identifying the predominant pain phenotype in people with CTS-related pain, albeit CTS being a priori a neuropathic pain condition. The identification of a nociplastic-associated condition requires a more nuanced multimodal treatment approach to achieve better treatment outcomes.

Phenotyping Post-COVID Pain as a Nociceptive, Neuropathic, or Nociplastic Pain Condition

Pain after an acute Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019 (COVID-19) condition (post-COVID pain) is becoming a new healthcare emergency. Precision medicine refers to an evidence-based method of grouping patients based on their diagnostic/symptom presentation and then tailoring specific treatments accordingly. Evidence suggests that post-COVID pain can be categorized as nociceptive (i.e., pain attributable to the activation of the peripheral receptive terminals of primary afferent neurons in response to noxious chemical, mechanical, or thermal stimuli), neuropathic (i.e., pain associated with a lesion or disease of the somatosensory nervous system and limited to a “neuroanatomically plausible” distribution of the system), nociplastic (i.e., pain arising from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain), or mixed type (when two pain phenotypes co-exist). Each of these pain phenotypes may require a different treatment approach to maximize treatment effectiveness. Accordingly, the ability to classify post-COVID pain patients into one of these phenotypes would likely be critical for producing successful treatment outcomes. The 2021 International Association for the Study of Pain (IASP) clinical criteria and grading system provide a framework for classifying pain within a precision pain medicine approach. Here we present data supporting the possibility of grouping patients with post-COVID pain into pain phenotypes, using the 2021 IASP classification criteria, with a specific focus on nociplastic pain, which is probably the primary mechanism involved in post-COVID pain. Nociplastic pain, which is usually associated with comorbid symptomology (e.g., poor sleep quality, fatigue, cognitive–emotional disturbances, etc.) and is considered to be more difficult to treat than other pain types, may require a more nuanced multimodal treatment approach to achieve better treatment outcomes.

Do Short-Term Effects Predict Long-Term Improvements in Women Who Receive Manual Therapy or Surgery for Carpal Tunnel Syndrome? A Bayesian Network Analysis of a Randomized Clinical Trial

OBJECTIVE

The purpose of this study was to develop a data-driven Bayesian network approach to understand the potential multivariate pathways of the effect of manual physical therapy in women with carpal tunnel syndrome (CTS).

METHODS

Data from a randomized clinical trial (n = 104) were analyzed comparing manual therapy including desensitization maneuvers of the central nervous system versus surgery in women with CTS. All variables included in the original trial were included in a Bayesian network to explore its multivariate relationship. The model was used to quantify the direct and indirect pathways of the effect of physical therapy and surgery on short-term, mid-term, and long-term changes in the clinical variables of pain, related function, and symptom severity.

RESULTS

Manual physical therapy improved function in women with CTS (between-groups difference: 0.09; 95% CI = 0.07 to 0.11). The Bayesian network showed that early improvements (at 1 month) in function and symptom severity led to long-term (at 12 months) changes in related disability both directly and via complex pathways involving baseline pain intensity and depression levels. Additionally, women with moderate CTS had 0.14-point (95% CI = 0.11 to 0.17 point) poorer function at 12 months than those with mild CTS and 0.12-point (95% CI = 0.09 to 0.15 point) poorer function at 12 months than those with severe CTS.

CONCLUSION

Current findings suggest that short-term benefits in function and symptom severity observed after manual therapy/surgery were associated with long-term improvements in function, but mechanisms driving these effects interact with depression levels and severity as assessed using electromyography. Nevertheless, it should be noted that between-group differences depending on severity determined using electromyography were small, and the clinical relevance is elusive. Further data-driven analyses involving a broad range of biopsychosocial variables are recommended to fully understand the pathways underpinning CTS treatment effects.

IMPACT

Short-term effects of physical manual therapy seem to be clinically relevant for obtaining long-term effects in women with CTS.

Understanding the Psychophysiological Mechanisms Related to Widespread Pressure Pain Hyperalgesia Underpinning Carpal Tunnel Syndrome: A Network Analysis Approach

OBJECTIVE

Current evidence suggests that carpal tunnel syndrome (CTS) involves widespread pressure pain sensitivity as manifestion of central sensitization. This study aimed to quantify mechanisms driving widespread pressure pain hyperalgesia in CTS by using network analysis.

DESIGN

Cross-sectional.

SETTING

Urban hospital.

SUBJECTS

120 women with CTS who participated in a previous randomized clinical trial.

METHODS

Pain intensity, related-function, symptom's severity, depressive levels, and pressure pain threshold (PPTs) over median, radial and ulnar nerves, the cervical spine, the carpal tunnel, and the tibialis anterior were collected. Network analysis was used to quantify the adjusted correlations between the modelled variables, and to determine the centrality indices of each variable (i.e., the degree of connection with other symptoms in the network).

RESULTS

The estimated network showed several local associations between clinical variables and the psychophysical outcomes separately. The edges with the strongest weights were between PPT over the median and radial nerves (ρ: 0.34), function and depressive levels (ρ: 0.30), and PPT over the carpal tunnel and tibialis anterior (ρ: 0.29). The most central variables were PPT over the tibialis anterior (the highest Strength centrality), and PPT over the carpal tunnel (the highest Closeness and Betweenness centrality).

CONCLUSIONS

This is the first study to apply network analysis to understand the multivariate mechanisms of individuals with CTS. Our findings support a model where clinical, depression, and widespread pressure pain sensitivity are connected, albeit within separate clusters. Clinical implications of current findings, such as developing treatments targeting these mechanisms, are also discussed.

Spectral Clustering Reveals Different Profiles of Central Sensitization in Women with Carpal Tunnel Syndrome

Identification of subgroups of patients with chronic pain provides meaningful insights into the characteristics of a specific population, helping to identify individuals at risk of chronification and to determine appropriate therapeutic strategies. This paper proposes the use of spectral clustering (SC) to distinguish subgroups (clusters) of individuals with carpal tunnel syndrome (CTS), making use of the obtained patient profiling to argue about potential management implications. SC is a powerful algorithm that builds a similarity graph among the data points (the patients), and tries to find the subsets of points that are strongly connected among themselves, but weakly connected to others. It was chosen due to its advantages with respect to other simpler clustering techniques, such as k-means, and the fact that it has been successfully applied to similar problems. Clinical (age, duration of symptoms, pain intensity, function, and symptom severity), psycho-physical (pressure pain thresholds—PPTs—over the three main nerve trunks of the upper extremity, cervical spine, carpal tunnel, and tibialis anterior), psychological (depressive levels), and motor (pinch tip grip force) variables were collected in 208 women with clinical/electromyographic diagnosis of CTS, whose symptoms usually started unilaterally but eventually evolved into bilateral symmetry. SC was used to identify clusters of patients without any previous assumptions, yielding three clusters. Patients in cluster 1 exhibited worse clinical features, higher widespread pressure pain hyperalgesia, higher depressive levels, and lower pinch tip grip force than the other two. Patients in cluster 2 showed higher generalized thermal pain hyperalgesia than the other two. Cluster 0 showed less hypersensitivity to pressure and thermal pain, less severe clinical features, and more normal motor output (tip grip force). The presence of subgroups of individuals with different altered nociceptive processing (one group being more sensitive to pressure pain and another group more sensitive to thermal pain) could lead to different therapeutic programs.

Applications of Marine Organism-Derived Polydeoxyribonucleotide: Its Potential in Biomedical Engineering

Polydeoxyribonucleotides (PDRNs) are a family of DNA-derived drugs with a molecular weight ranging from 50 to 1500 kDa, which are mainly extracted from the sperm cells of salmon trout or chum salmon. Many pre-clinical and clinical studies have demonstrated the wound healing and anti-inflammatory properties of PDRN, which are mediated by the activation of adenosine A2A receptor and salvage pathways, in addition to promoting osteoblast activity, collagen synthesis, and angiogenesis. In fact, PDRN is already marketed due to its therapeutic properties against various wound healing- and inflammation-related diseases. Therefore, this review assessed the most recent trends in marine organism-derived PDRN using the Google Scholar search engine. Further, we summarized the current applications and pharmacological properties of PDRN to serve as a reference for the development of novel PDRN-based technologies.

Manual Therapy Versus Surgery for Carpal Tunnel Syndrome: 4-Year Follow-Up From a Randomized Controlled Trial

OBJECTIVE

No study to our knowledge has investigated the effects longer than 1 year of manual therapy in carpal tunnel syndrome (CTS). The purpose of this study was to investigate the effects of manual therapy versus surgery at 4-year follow-up and to compare the post-study surgery rate in CTS.

METHODS

This randomized controlled trial was conducted in a tertiary public hospital and included 120 women with CTS who were randomly allocated to manual therapy or surgery. The participants received 3 sessions of physical therapy, including desensitization maneuvers of the central nervous system or carpal tunnel release combined with a tendon/nerve gliding exercise program at home. Primary outcome was pain intensity (mean and the worst pain). Secondary outcomes included functional status, symptom severity, and self-perceived improvement measured using a global rating of change scale. Outcomes for this analysis were assessed at baseline, 1 year, and 4 years. The rate of surgical intervention received by each group was assessed throughout the study.

RESULTS

At 4 years, 97 (81%) women completed the study. Between-group changes for all outcomes were not significantly different at 1 year (mean pain: mean difference [MD] = -0.3, 95% CI = -0.9 to 0.3; worst pain: MD = -1.2, 95% CI = -3.6 to 1.2; function: MD = -0.1, 95% CI = -0.4 to 0.2; symptom severity: MD = -0.1, 95% CI = -0.3 to 0.1) and 4 years (mean pain: MD = 0.1, 95% CI = -0.2 to 0.4; worst pain: MD = 0.2, 95% CI = -0.8 to 1.2; function: MD = 0.1, 95% CI = -0.1 to 0.3; symptom severity: MD = 0.2, 95% CI = -0.2 to 0.6). Self-perceived improvement was also similar in both groups. No between-group differences (15% physical therapy vs 13% surgery) in surgery rate were observed during the 4 years.

CONCLUSIONS

In the long term, manual therapy, including desensitization maneuvers of the central nervous system, resulted in similar outcomes and similar surgery rates compared with surgery in women with CTS. Both interventions were combined with a tendon/nerve gliding exercise program at home.

IMPACT

This is the first study to our knowledge to report clinical outcomes and surgical rates during a 4-year follow-up and will inform decisions regarding surgical versus conservative management of CTS.

LAY SUMMARY

Women with CTS may receive similar benefit from a more conservative treatment-manual therapy-as they would from surgery.

Mathematical Modeling for Neuropathic Pain: Bayesian Linear Regression and Self-Organizing Maps Applied to Carpal Tunnel Syndrome

A better understanding of the connection between risk factors associated with pain and function may assist therapists in optimizing therapeutic programs. This study applied mathematical modeling to analyze the relationship of psychological, psychophysical, and motor variables with pain, function, and symptom severity using Bayesian linear regressions (BLR) and self-organizing maps (SOMs) in carpal tunnel syndrome (CTS). The novelty of this work was a transfer of the symmetry mathematical background to a neuropathic pain condition, whose symptoms can be either unilateral or bilateral. Duration of symptoms, pain intensity, function, symptom severity, depressive levels, pinch tip grip force, and pressure pain thresholds (PPTs) over the ulnar, radial, and median nerve trunks, the cervical spine, the carpal tunnel, and the tibialis anterior were collected in 208 women suffering from CTS. The first BLR model revealed that symptom severity, PPTs over the radial nerve, and function had significant correlations with pain intensity. The second BLR showed that symptom severity, depressive levels, pain intensity, and years with pain were associated with function. The third model demonstrated that pain intensity and function were associated with symptom severity. The SOMs visualized these correlations among variables, i.e., clinical, psychophysical, and physical, and identified a subgroup of women with CTS exhibiting worse clinical features, higher pressure sensitivity, and lower pinch tip grip force. Therefore, the application of mathematical modeling identified some interactions among the intensity of pain, function, and symptom severity in women with CTS.

Understanding central sensitization for advances in management of carpal tunnel syndrome

Carpal tunnel syndrome is the most common nerve compression disorder of the upper extremity, and it is traditionally considered a peripheral neuropathy associated with a localized compression of the median nerve just at the level of the carpal tunnel. Surgery and physiotherapy are treatment approaches commonly used for this condition; however, conflicting clinical outcomes suggest that carpal tunnel syndrome may be more complex. There is evidence supporting the role of peripheral nociception from the median nerve in carpal tunnel syndrome; however, emerging evidence also suggests a potential role of central sensitization. The presence of spreading pain symptoms (e.g. proximal pain), widespread sensory changes, or bilateral motor control impairments in people presenting with strictly unilateral sensory symptoms supports the presence of spinal cord changes. Interestingly, bilateral sensory and motor changes are not directly associated with electrodiagnostic findings. Other studies have also reported that patients presenting with carpal tunnel syndrome exhibit neuroplastic brainstem change supporting central sensitization. Current data would support the presence of a central sensitization process, mediated by the peripheral drive originating in the compression of the median nerve, in people with carpal tunnel syndrome. The presence of altered nociceptive gain processing should be considered in the treatment of carpal tunnel syndrome by integrating therapeutic approaches aiming to modulate long-lasting nociceptive barrage into the central nervous system (peripheral drive) and strategies aiming to activate endogenous pain networks (central drive).