It is one or the other: No overlap between healthy individuals perceiving thermal grill illusion or paradoxical heat sensation.

Paradoxical heat sensation (PHS) and the thermal grill illusion (TGI) are both related to the perception of warmth or heat from innocuous cold stimuli. Despite being described as similar perceptual phenomena, recent findings suggested that PHS is common in neuropathy and related to sensory loss, while TGI is more frequently observed in healthy individuals. To clarify the relationship between these two phenomena, we conducted a study in a cohort of healthy individuals to investigate the association between PHS and TGI. We examined the somatosensory profiles of 60 healthy participants (34 females, median age 25 years) using the quantitative sensory testing (QST) protocol from the German Research Network on Neuropathic Pain. The number of PHS was measured using a modified thermal sensory limen (TSL) procedure where the skin was transiently pre-warmed, or pre-cooled before the PHS measure. This procedure also included a control condition with a pre-temperature of 32 °C. The number of TGI responses was quantified during simultaneous application of warm and cold innocuous stimuli. All participants had normal thermal and mechanical thresholds compared to the reference values from the QST protocol. Only two participants experienced PHS during the QST procedure. In the modified TSL procedure, we found no statistically significant differences in the number of participants reporting PHS in the control condition (N = 6) vs. pre-warming (N = 3; min = 35.7 °C, max = 43.5 °C) and pre-cooling (N = 4, min = 15.0 °C, max = 28.8 °C) conditions. Fourteen participants experienced TGI, and only one participant reported both TGI and PHS. Individuals with TGI had normal or even increased thermal sensation compared to individuals without TGI. Our findings demonstrate a clear distinction between individuals experiencing PHS or TGI, as there was no overlap observed when using identical warm and cold temperatures that were alternated either temporally or spatially. While PHS was previously related to sensory loss, our study revealed that TGI is associated with normal thermal sensitivity. This suggests that an efficient thermal sensory function is essential in generating the illusory sensation of pain of the TGI.

Perioperative factors associated with persistent postsurgical pain after hysterectomy, cesarean section, prostatectomy, and donor nephrectomy: a systematic review and meta-analysis.

ABSTRACT: Persistent postsurgical pain (PPSP) is a common and often disabling postoperative morbidity, but many questions remain about factors associated with PPSP. This systematic review and meta-analysis aimed to identify preoperative, intraoperative, and postoperative factors associated with PPSP after gynecological surgeries, namely, hysterectomy and cesarean section, and urological surgeries, namely, prostatectomy and donor nephrectomy. Overall, 18 gynecological surgery studies, 4 prostatectomy studies, and 2 donor nephrectomy studies met the review criteria, providing data that could be meta-analyzed. The average (±SD) PPSP occurrence after gynecological surgery was 20 ± 11%; factors associated with increased risk of PPSP included smoking, preoperative abdominal or pelvic pain, preoperative pain elsewhere in the body, longer duration of surgery, more intense acute postoperative pain, and surgical wound infection. The use of neuraxial anesthesia was associated with decreased PPSP risk. The average PPSP occurrence was 20 ± 9% after prostatectomy and 15 ± 2% after donor nephrectomy. For urological procedures, the existing data did not allow for identification of significant factors associated with PPSP, except for laparoscopic and hand-assisted laparoscopic approaches that were associated with lower incidence of PPSP for donor nephrectomy, and the use of neuraxial anesthesia which was associated with lower incidence of PPSP after prostatectomy. Persistent postsurgical pain after gynecological and urological surgeries is common. This systematic review identified important factors associated with cesarean section and hysterectomy that can help identify women who are at high risk of PPSP. More high-quality studies with consistent methodology are needed to understand the factors associated with PPSP risk, particularly for surgeries such as prostatectomy and nephrectomy.

No association of polymorphisms in the serotonin transporter gene with thermal pain sensation in healthy individuals.

BACKGROUND: Recent studies have suggested an association between genotypes affecting the expression of the serotonin transporter and thermal pain perception and the thermal grill. The aim of this study was to investigate differences in thermal and mechanical pain perception and the thermal grill in two groups of healthy volunteers according to their genotype, associated with either high (n = 40) or low (n = 40) expression of the serotonin transporter and according to gender. Cold and warm detection and pain thresholds, pressure pain threshold and cold, warm and pain sensations to single or alternating stimuli with cold (20°C) and warm (40°C) temperatures (known as the thermal grill) were determined. In addition, intensity of ongoing pain and area and intensity of pinprick hyperalgesia in the secondary hyperalgesic area following topical application of capsaicin and vehicle control (ethanol) were determined. RESULTS: No significant differences in detection and pain thresholds for cold and warm temperatures, presence of paradoxical heat sensation, pressure pain threshold and pain responses to suprathreshold thermal stimuli were observed. There was also no difference in capsaicin-evoked ongoing pain and secondary hyperalgesia between the two genotype groups (p >0.4), also when subdivided by gender (p >0.17). In addition, there were no significant differences in the perception of the thermal grill between the two genotypes (p >0.5), also when subdivided by gender. CONCLUSIONS: Genotypes associated with high or low expression of the serotonin transporter were not associated with thermal pain thresholds, pressure pain threshold, pain after capsaicin application or responses to the thermal grill.The present results do not support that the investigated genotypes play a major role in thermal pain perception among healthy individuals.