Blood monoamines as potential biomarkers for conditioned pain modulation efficacy: An exploratory study in paediatrics

Clusters of facilitatory and inhibitory conditioned pain modulation responses in a large sample of children, adolescents, and young adults with chronic pain

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Findings from the current study add to the literature by describing different clinical phenotypes of central pain mechanisms of youth with chronic pain.

Introduction:

When investigating the role of facilitatory and inhibitory pain mechanisms such as conditioned pain modulation (CPM) and temporal summation of pain (TSP), it is important to take both into consideration in a single experimental model to provide the most information on subgroups of patients. Therefore, the objective of this study was to identify subgroups in a large population of pediatric patients with chronic pain based on their facilitatory and inhibitory pain mechanisms and compare them with control subjects.

Methods:

Five hundred twenty-one female subjects and 147 male subjects between 8 and 21 years old underwent a CPM assessment using a 2-minute tonic noxious heat stimulation as the test stimulus and a 2-minute cold-pressor task (CPT) (12°C) as the conditioning stimulus.

Results:

The best partition of clusters of patients was 3 clusters accounting for 27.15% of the total variation in the data. Cluster 1 (n = 271) was best characterized by high pain intensity during the CPT, lack of TSP during the test stimuli, and efficient inhibitory CPM. Cluster 2 (n = 186) was best characterized by low pain intensity during the CPT, lack of TSP during the test stimuli, and efficient inhibitory CPM. Cluster 3 (n = 151) was best characterized by high pain intensity during the CPT, presence of TSP during the test stimuli, and inefficient inhibitory CPM.

Discussion:

A single thermal CPM experimental design can identify combinations of facilitatory and inhibitory pain modulation responses. Findings from the current study add to the literature by describing different clinical phenotypes of central pain mechanisms of youth with chronic pain.

Toward Composite Pain Biomarkers of Neuropathic Pain—Focus on Peripheral Neuropathic Pain

Chronic pain affects ~10–20% of the U.S. population with an estimated annual cost of $600 billion, the most significant economic cost of any disease to-date. Neuropathic pain is a type of chronic pain that is particularly difficult to manage and leads to significant disability and poor quality of life. Pain biomarkers offer the possibility to develop objective pain-related indicators that may help diagnose, treat, and improve the understanding of neuropathic pain pathophysiology. We review neuropathic pain mechanisms related to opiates, inflammation, and endocannabinoids with the objective of identifying composite biomarkers of neuropathic pain. In the literature, pain biomarkers typically are divided into physiological non-imaging pain biomarkers and brain imaging pain biomarkers. We review both types of biomarker types with the goal of identifying composite pain biomarkers that may improve recognition and treatment of neuropathic pain.

Phenotyping Chronic Musculoskeletal Pain in Male and Female Adolescents: Psychosocial Profiles, Somatosensory Profiles and Pain Modulatory Profiles

Purpose

A major limitation in treatment outcomes for chronic pain is the heterogeneity of the population. Therefore, a personalized approach to the assessment and treatment of children and adolescents with chronic pain conditions is needed. The objective of the study was to subgroup pediatric patients with chronic MSK pain that will be phenotypically different from each other based on their psychosocial profile, somatosensory function, and pain modulation.

Patients and Methods

This observational cohort study recruited 302 adolescents (10–18 years) with chronic musculoskeletal pain and 80 age-matched controls. After validated self-report questionnaires on psychosocial factors were completed, quantitative sensory tests (QST) and conditioned pain modulation (CPM) were performed.

Results

Three psychosocial subgroups were identified: adaptive pain (n=125), high pain dysfunctional (n=115), high somatic symptoms (n=62). Based on QST, four somatosensory profiles were observed: normal QST (n=155), thermal hyperalgesia (n=98), mechanical hyperalgesia (n=34) and sensory loss (n=15). Based on CPM and temporal summation of pain (TSP), four distinct groups were formed, dysfunctional central processing group (n=27) had suboptimal CPM and present TSP, dysfunctional inhibition group (n=136) had suboptimal CPM and absent TSP, facilitation group (n=18) had optimal CPM and present TSP, and functional central processing (n=112) had optimal CPM and absent TSP. A significant association between the psychosocial and somatosensory profiles. However, no association was observed between the psychosocial or somatosensory profiles and pain modulatory profiles.

Conclusion

Our results provide evidence that adolescents with chronic musculoskeletal pain are a heterogenous population comprising subgroups that may reflect distinct mechanisms and may benefit from different treatment approaches. The combination of screening self-reported questionnaires, QST, and CPM facilitate subgrouping of adolescents with chronic MSK pain in the clinical context and may ultimately contribute to personalized therapy.

Psychosocial and psychophysical assessment in pediatric patients and young adults with chronic back pain: a cluster analysis

Background

Identifying subgroups with different clinical profiles may inform tailored management and improve outcomes. The objective of this study was to identify psychosocial and psychophysical profiles of children and adolescents with chronic back pain.

Methods

One hundred and ninety‐eight patients with chronic back pain were recruited for the study. Pain assessment was mainly conducted in the form of an interview and with the use of validated pain‐related questionnaires assessing their psychosocial factors and disability. All patients underwent mechanical and thermal quantitative sensory tests assessing detection and pain thresholds, and conditioned pain modulation efficacy.

Results

Hierarchal clustering partitioned our patients into three clusters accounting for 34.73% of the total variation of the data. The adaptive cluster represented 45.5% of the patients and was characterized to display high thermal and pressure pain thresholds. The high somatic symptoms cluster, representing 19.2% of patients, was characterized to use more sensory, affective, evaluative and temporal descriptors of pain, more likely to report their pain as neuropathic of nature, report a more functional disability, report symptoms of anxiety and depression and report poor sleep quality. The pain‐sensitive cluster, representing 35.4% of the cohort, displayed deep tissue sensitivity and thermal hyperalgesia.

Conclusions

This study identified clinical profiles of children and adolescents experiencing chronic back pain based on specific psychophysical and psychosocial characteristics highlighting that chronic pain treatment should address underlying nociceptive and non‐nociceptive mechanisms.

Significance

To our current knowledge, this study is the first to conduct cluster analysis with youth experiencing chronic back pain and displays clinical profiles based on specific physical and psychosocial characteristics. This study highlights that in a clinical context, chronic pain assessment should include multiple elements contributing to pain which can be assessed in a clinical context and addressed when pathoanatomical symptoms are unidentifiable.

Association of Peripheral Plasma Neurotransmitters with Cognitive Performance in Chronic High-altitude Exposure

Long-term living at high altitude causes significant impairment of cognitive function. Central neurotransmitters are potential mediators of cognitive performance. We aimed to determine whether there were significant associations between select peripheral plasma neurotransmitters and cognitive performance in humans with chronic high-altitude (HA) exposure and to determine the association between peripheral plasma neurotransmitters and brain neurotransmitters in rats after chronic hypobaric hypoxia (HH) exposure. We demonstrated that 3,4-dihydroxy-L-phenylalanine (DOPA), dopamine, serotonin, 5-hydroxyindole-3-acetic acid (5-HIAA) and GABA in the peripheral plasma were associated with cognitive performance in humans with HA exposure. Consistent with this result, peripheral plasma DOPA, dopamine, serotonin, 5-HIAA and glutamate were associated with brain neurotransmitter levels after chronic HH exposure in rats. These results provide experimental data indicating that neurotransmitter levels and cognitive performance are modified in chronic high-altitude exposure, with a possible causal effect.

Urinary Amine and Organic Acid Metabolites Evaluated as Markers for Childhood Aggression: The ACTION Biomarker Study

Biomarkers are of interest as potential diagnostic and predictive instruments in personalized medicine. We present the first urinary metabolomics biomarker study of childhood aggression. We aim to examine the association of urinary metabolites and neurotransmitter ratios involved in key metabolic and neurotransmitter pathways in a large cohort of twins (N = 1,347) and clinic-referred children (N = 183) with an average age of 9.7 years. This study is part of ACTION (Aggression in Children: Unraveling gene-environment interplay to inform Treatment and InterventiON strategies), in which we developed a standardized protocol for large-scale collection of urine samples in children. Our analytical design consisted of three phases: a discovery phase in twins scoring low or high on aggression (N = 783); a replication phase in twin pairs discordant for aggression (N = 378); and a validation phase in clinical cases and matched twin controls (N = 367). In the discovery phase, 6 biomarkers were significantly associated with childhood aggression, of which the association of O-phosphoserine (β = 0.36; SE = 0.09; p = 0.004), and gamma-L-glutamyl-L-alanine (β = 0.32; SE = 0.09; p = 0.01) remained significant after multiple testing. Although non-significant, the directions of effect were congruent between the discovery and replication analyses for six biomarkers and two neurotransmitter ratios and the concentrations of 6 amines differed between low and high aggressive twins. In the validation analyses, the top biomarkers and neurotransmitter ratios, with congruent directions of effect, showed no significant associations with childhood aggression. We find suggestive evidence for associations of childhood aggression with metabolic dysregulation of neurotransmission, oxidative stress, and energy metabolism. Although replication is required, our findings provide starting points to investigate causal and pleiotropic effects of these dysregulations on childhood aggression.