Adaptive neuroplasticity in the default mode network contributing to absence of central sensitization in primary dysmenorrhea

Introduction

Primary dysmenorrhea (PDM), the most prevalent gynecological problem among women of reproductive age, presents as a regular pattern of cyclic menstrual pain. The presence or absence of central sensitization (i.e., pain hypersensitivity) in cases of PDM is a contentious issue. Among Caucasians, the presence of dysmenorrhea is associated with pain hypersensitivity throughout the menstrual cycle, indicating pain amplification mediated by the central nervous system. We previously reported on the absence of central sensitization to thermal pain among Asian PDM females. In this study, functional magnetic resonance imaging was used to reveal mechanisms underlying pain processing with the aim of explaining the absence of central sensitization in this population.

Methods

Brain responses to noxious heat applied to the left inner forearm of 31 Asian PDM females and 32 controls during their menstrual and periovulatory phases were analyzed.

Results and discussion

Among PDM females experiencing acute menstrual pain, we observed a blunted evoked response and de-coupling of the default mode network from the noxious heat stimulus. The fact that a similar response was not observed in the non-painful periovulatory phase indicates an adaptive mechanism aimed at reducing the impact of menstrual pain on the brain with an inhibitory effect on central sensitization. Here we propose that adaptive pain responses in the default mode network may contribute to the absence of central sensitization among Asian PDM females. Variations in clinical manifestations among different PDM populations can be attributed to differences in central pain processing.

Thermal quantitative sensory testing in healthy Dutch children and adolescents standardized test paradigm and Dutch reference values

Background

Quantitative sensory testing (QST) is often used to measure children’s and adults’ detection- and pain thresholds in a quantitative manner. In children especially the Thermal Sensory Analyzer (TSA-II) is often applied to determine thermal detection and pain thresholds. As comparisons between studies are hampered by the different testing protocols used, we aimed to present a standard protocol and reference values for thermal detection- and pain thresholds in children.

Methods

Our standard testing protocol includes reaction time dependent and independent tests and takes about 14–18 min to complete. Reference values were obtained from a sample of 69 healthy term born children and adolescents with a median age of 11.2 years (range 8.2 to 17.9 years old). Seventy-one children were recruited and data of 28 males and 41 females was obtained correctly. We studied possible age and sex differences.

Results

This study provides Dutch reference values and presents a standard quantitative sensory testing protocol for children with an age from 8 years onwards. This protocol appeared to be feasible, since only two out of 71 participants were not able to correctly complete the protocol due to attention deficits and were therefore excluded. We found some significant age and sex differences: females were statistically significantly more sensitive for both cold and heat pain compared to males, and the youngest children (8–9 years old) were less sensitive to detect a warm stimulus. The youngest children tend to be more sensitive to heat pain in comparison to older participants, although the difference was not statistically significant.

Conclusions

We present a feasible thermal quantitative sensory testing protocol for children and reference values that are easy to interpret and may serve as normative values for future studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-017-0827-7) contains supplementary material, which is available to authorized users.

Neuroimaging, Pain Sensitivity, and Neuropsychological Functioning in School-Age Neonatal Extracorporeal Membrane Oxygenation Survivors Exposed to Opioids and Sedatives

OBJECTIVES

Animal studies found negative long-term effects of exposure to sedatives and opioids in early life, especially when administered in the absence of pain. Around the world, children who require extracorporeal membrane oxygenation receive opioids and sedatives for extended periods, generally in the absence of major pain as extracorporeal membrane oxygenation cannulation is considered minor surgery. Therefore, our objective was to determine the long-term effects of extracorporeal membrane oxygenation treatment with respect to pain sensitivity, brain functioning during pain, brain morphology, and neuropsychological functioning in humans.

DESIGN

Prospective follow-up study.

SETTING

Level III university hospital.

SUBJECTS

Thirty-six extracorporeal membrane oxygenation survivors (8.1-15.5 yr) and 64 healthy controls (8.2-15.3 yr).

MEASUREMENTS AND MAIN RESULTS

We measured detection and pain thresholds, brain activity during pain (functional MRI), brain morphology (high-resolution structural MRI), and neuropsychological functioning and collected information regarding the subject's experience of chronic pain. We found a significant difference in the detection threshold for cold measured in a reaction time-dependent fashion (extracorporeal membrane oxygenation group, 29.9°C [SD, 1.4]; control group, 30.6°C [SD, 0.8]; p < 0.01), but no differences in other modalities or in pain sensitivity between groups. Furthermore, no differences in brain activation during pain, brain morphology, or in the occurrence of chronic pain were observed. However, extracorporeal membrane oxygenation survivors performed significantly worse on a verbal memory test compared with controls (p = 0.001).

CONCLUSIONS

While the most critically ill newborns receive extracorporeal membrane oxygenation and, relatedly, large doses of opioids and sedatives for extended periods, global measures of pain sensitivity and neurobiological and neuropsychological development appear to have minor long-term consequences. Possible memory deficits in extracorporeal membrane oxygenation survivors require additional study, but neonatal extracorporeal membrane oxygenation treatment and associated exposure to opioids and sedatives seem less harmful to humans than expected from animal studies.

Intersession reliability of fMRI activation for heat pain and motor tasks

As the practice of conducting longitudinal fMRI studies to assess mechanisms of pain-reducing interventions becomes more common, there is a great need to assess the test–retest reliability of the pain-related BOLD fMRI signal across repeated sessions. This study quantitatively evaluated the reliability of heat pain-related BOLD fMRI brain responses in healthy volunteers across 3 sessions conducted on separate days using two measures: (1) intraclass correlation coefficients (ICC) calculated based on signal amplitude and (2) spatial overlap. The ICC analysis of pain-related BOLD fMRI responses showed fair-to-moderate intersession reliability in brain areas regarded as part of the cortical pain network. Areas with the highest intersession reliability based on the ICC analysis included the anterior midcingulate cortex, anterior insula, and second somatosensory cortex. Areas with the lowest intersession reliability based on the ICC analysis also showed low spatial reliability; these regions included pregenual anterior cingulate cortex, primary somatosensory cortex, and posterior insula. Thus, this study found regional differences in pain-related BOLD fMRI response reliability, which may provide useful information to guide longitudinal pain studies. A simple motor task (finger-thumb opposition) was performed by the same subjects in the same sessions as the painful heat stimuli were delivered. Intersession reliability of fMRI activation in cortical motor areas was comparable to previously published findings for both spatial overlap and ICC measures, providing support for the validity of the analytical approach used to assess intersession reliability of pain-related fMRI activation. A secondary finding of this study is that the use of standard ICC alone as a measure of reliability may not be sufficient, as the underlying variance structure of an fMRI dataset can result in inappropriately high ICC values; a method to eliminate these false positive results was used in this study and is recommended for future studies of test–retest reliability.

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Intersession reliability of pain-related fMRI responses was fair-to-moderate

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Intersession reliability of pain-related fMRI responses varied by brain region

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Intersession reliability is comparable for fixed temperature and fixed perception stimuli

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Standard methods of assessing intersession reliability can lead to false positives

Pain insensitivity syndrome misinterpreted as inflicted burns

We present a case study of a 10-year-old child with severe burns that were misinterpreted as inflicted burns. Because of multiple injuries since early life, the family was under suspicion of child abuse and therefore under supervision of the Child Care Board for 2 years before the boy was burned. Because the boy incurred the burns without feeling pain, we conducted a thorough medical examination and laboratory testing, evaluated detection and pain thresholds, and used MRI to study brain morphology and brain activation patterns during pain between this patient and 3 healthy age- and gender-matched controls. We found elevated detection and pain thresholds and lower brain activation during pain in the patient compared with the healthy controls and reference values. The patient received the diagnosis of hereditary sensory and autonomic neuropathy type IV on the basis of clinical findings and the laboratory testing, complemented with the altered pain and detection thresholds and MRI findings. Hereditary sensory and autonomic neuropathy IV is a very rare congenital pain insensitivity syndrome characterized by the absence of pain and temperature sensation combined with oral mutilation due to unawareness, fractures, and anhidrosis caused by abnormalities in the peripheral nerves. Health care workers should be aware of the potential presence of this disease to prevent false accusations of child abuse.