Human Studies

Healthy women have generally been found to have increased experimental pain perception and chronic pain has a higher prevalence in female as compared to male patients. However, no study has investigated whether pain intensity and pain perception thresholds are distinct or similar between sexes within various chronic pain entities. We investigated whether average pain intensities and pain thresholds assessed using quantitative sensory testing (QST) differed between women and men suffering from three distinct chronic pain conditions: Complex Regional Pain Syndrome (CRPS type I), peripheral nerve injury (PNI) or polyneuropathy (PNP), as compared to paired healthy volunteers.

To assess differences in tactile spatial acuity and in sensory-motor control between patients with chronic nonspecific neck pain (CNSNP) with and without neuropathic features (NF), as well as asymptomatic.

Limited information on the prevalence and risk factors for chronic pain is available for developing countries. Therefore, we investigated the prevalence of chronic pain, and the association between this pain and various personal and sociodemographic factors by including questions in the South Africa Demographic and Household Survey 2016. The survey was conducted by face-to-face interviews with a nationally representative sample of the adult population (ages 15 and older, n = 10336). Chronic pain was defined as pain or discomfort that had been experienced all the time or on and off for three months or more. The prevalence of chronic pain was 18.3% [95% CI: 17.0, 19.7]. Women were more likely than were men to have chronic pain (Men = 15.8% [95% CI: 13.9, 17.8]; Woman = 20.1% [95% CI: 18.4, 21.8]), and the prevalence of chronic pain increased from 11.3% [95% CI: 9.6, 13.3] for the age range 15-24 years to 34.4% [95% CI: 30.6, 38.4] for the age range over 65 years. The body sites affected most frequently were the limbs (43.6% [95% CI: 40.4, 46.9]), followed by the back (30.5% [95% CI: 27.7, 33.6]). This article presents the prevalence of chronic pain in the general population of a middle-income African country. These data give much needed insights into the burden of, and risk factors for, chronic pain in low-resource settings, and identify priority groups for intervention.

Mechanisms underpinning ongoing symptoms in chronic whiplash associated-disorder (WAD) are not well understood. People with chronic WAD can exhibit sensory dysfunction consistent with small nerve fibre pathology, including thermal hypoaesthesia and hyperalgesia. This study investigated small fibre structure and function in chronic WAD.

Prevalence of functional somatic syndromes (FSS) in the general population varies with observed overlap between syndromes. However, studies including a range of FSS are sparse. We investigated prevalence and characteristics of various FSS and the unifying diagnostic construct bodily distress syndrome (BDS), and identified mutual overlap of the FSS and their overlap with BDS. We included a stratified subsample of 1590 adults from a randomly selected Danish general population sample (n = 7493). Telephonic diagnostic interviews performed by three trained physicians were used to identify individuals with FSS and BDS. Prevalence of overall FSS was 9.3%; 3.8% for irritable bowel, 2.2% for chronic widespread pain, 6.1% for chronic fatigue, 1.5% for whiplash associated disorders, and 0.9% for multiple chemical sensitivity. Prevalence of BDS was 10.7% where 2.0% had the multi-organ type. FSS were highly overlapping with low likelihood of having a "pure" type. Diagnostic agreement of FSS and BDS was 92.0%. Multi-syndromatic FSS and multi-organ BDS were associated with female sex, poor health, physical limitations, and comorbidity. FSS are highly prevalent and overlapping, and multi-syndromatic cases are most affected. BDS captured the majority of FSS and may improve clinical management, making the distinction between multi- and mono-syndromatic patients easier.

Whether, how, and which cognitive factors modulate the development of secondary hypersensitivity/hyperalgesia following central sensitization is not fully understood. Here we tested, in three subsequent experiments, whether being engaged in non-pain related cognitive demanding tasks: i) lessens the amount of hypersensitivity developed after an experimental procedure sensitizing nociceptive pathways; ii) modulates cortical responses to somatosensory stimuli (measured by electroencephalography, EEG). In the first experiment we validated a novel model in humans using low frequency stimulation (LFS) of the skin and demonstrated that it was able to successfully induce hypersensitivity to mechanical pinprick stimuli in the area surrounding the sensitized site. In the second and third experiments we engaged participants in tasks of increasing difficulty (the Eriksen Flanker Task in experiment 2, and a modified N-back task in experiment 3). We observed that hypersensitivity to mechanical stimuli still developed in experiment 2, i.e. the pinprick stimuli applied on the sensitized arm were perceived as more intense after LFS. In contrast, no statistically significant enhancement of mechanical hypersensitivity was observed in experiment 3, indicating that, at the group level, being engaged in a difficult N-back task may interfere with the development of mechanical hypersensitivity. Contrary to previous studies, which have used different methods to induce sensitization, we did not observe any increase in the cortical response to somatosensory stimuli applied on the sensitized arm. We conclude that i) the development of pinprick hypersensitivity is modulated by the concomitant execution of a difficult N-back task, and ii) the enhancement of cortical responses to somatosensory stimuli is related to the method used to induce central sensitization.