Effect of ketamine on endogenous pain modulation in healthy volunteers

Inhibitory and facilitatory descending pathways, originating at higher central nervous system sites, modulate activity of dorsal horn nociceptive neurons, and thereby influence pain perception. Dysfunction of inhibitory pain pathways or a shift in the balance between pain facilitation and pain inhibition has been associated with the development of chronic pain. The N-methyl-d-aspartate receptor antagonist ketamine has a prolonged analgesic effect in chronic pain patients. This effect is due to desensitization of sensitized N-methyl-d-aspartate receptors. Additionally, ketamine may modulate or enhance endogenous inhibitory control of pain perception. Diffuse noxious inhibitory control (DNIC) and offset analgesia (OA) are 2 mechanisms involved in descending inhibition. The present study investigates the effect of a ketamine infusion on subsequent DNIC and OA responses to determine whether ketamine has an influence on descending pain control. Ten healthy subjects (4 men/6 women) received a 1-hour placebo or S(+)-ketamine (40 mg per 70 kg) infusion on 2 separate occasions in random order. Upon the termination of the infusion, DNIC and OA responses were obtained. After placebo treatment, significant descending inhibition of pain responses was present for DNIC and OA. In contrast, after ketamine infusion, no DNIC was observed, but rather a significant facilitatory pain response (P < 0.01); the OA response remained unchanged. These findings suggest that the balance between pain inhibition and pain facilitation was shifted by ketamine towards pain facilitation. The absence of an effect of ketamine on OA indicates differences in the mechanisms and neurotransmitter influences between OA and DNIC.     

TRPV1 antagonistic analgesic effect: A randomized study of AZD1386 in pain after third molar extraction

The effects of a TRPV1 antagonist (AZD1386) were investigated in patients with acute pain. After removal of a mandibular third molar and at request of analgesia 103 patients randomly received 95 mg AZD1386 (n = 40), placebo (n = 40) or 500 mg naproxen (n = 23) in a double-blind manner. Plasma samples were drawn, and pain intensity and body temperature were measured during 8 h after drug administration. The pain intensity difference from drug intake was calculated as a percentage (PID%) and as a weighted sum over the 8 h (SPID%_0–8h). The time to first perceptible and first meaningful pain relief was recorded. SPID%_0–8h showed no significant difference between AZD1386 and placebo (P = .132) but between naproxen and placebo (P = .038). AZD1386 had a rapid short-lasting analgesia and compared to placebo, PID% was significantly higher (P ? .026) at 0.25, 0.50, 0.75 and 1.00 h after drug administration. Correspondingly, for naproxen significantly higher PID% (P ? .021) was seen at 2.5, 3, 4, 5, 6, 7 and 8 h. The frequency of patients obtaining perceptible and meaningful pain relief was about 85% and 48% after AZD1386 and about 53% and 25% after placebo. The occurrence of perceptible and meaningful pain relief was significantly faster (P = .002 and P = .031) for AZD1386 compared to placebo. Adverse events were similar to placebo with the exception of 2 patients reporting chills. The highest individual body temperature after AZD1386 was 38.1°C, recorded in 2 patients. In summary, AZD1386 was well tolerated with a rapid analgesia that was short lasting despite sustained plasma concentration.     

An enriched-enrolment,randomized withdrawal,flexible-dose,double-blind,placebo-controlled,parallel assignment efficacy study of nabilone as adjuvant in the treatment of diabetic peripheral neuropathic pain

Cannabinoids are emerging as potential options for neuropathic pain treatment. This study evaluated an oral cannabinoid, nabilone, in the treatment of refractory human diabetic peripheral neuropathic pain (DPN). We performed a single-center, randomized, double-blind, placebo-controlled, flexible-dose study with an enriched enrolment randomized withdrawal design. DPN subjects with a pain score ?4 (0-10 scale) continued regular pain medications and were administered single-blinded adjuvant nabilone for 4 weeks. Subjects achieving ?30% pain relief (26/37) were then randomized and treated with either flexible-dose nabilone 1-4 mg/day (n = 13) or placebo (n = 13) in a further 5-week double-blind treatment period, with 30% (11/37) of subjects deemed run-in-phase nabilone nonresponders. For nabilone run-in-phase responders, there was an improvement in the change in mean end-point neuropathic pain vs placebo (mean treatment reduction of 1.27; 95% confidence interval 2.29-0.25, P = 0.02), with an average nabilone dose at end point of 2.9 ± 1.1 mg/day, and improvements from baseline for the anxiety subscale of the Hospital Anxiety and Depression Scale, the Medical Outcomes Study sleep scale problems index, and the European Quality of Life-5-Domains index score (each P < 0.05). Nabilone run-in-phase responders reported greater global end-point improvement with nabilone than with placebo (100% vs 31%; P < 0.05). Medication-related confusion led to discontinuation in 2/37 subjects during single-blind nabilone treatment. Potential unmasking occurred in 62% of both groups. Flexible-dose nabilone 1-4 mg/day was effective in relieving DPN symptoms, improving disturbed sleep, quality of life, and overall patient status. Nabilone was well tolerated and successful as adjuvant in patients with DPN.     

Low-dose amitriptyline for treatment of persistent arm pain due to repetitive use

Amitriptyline is sometimes used to treat arm pain related to repetitive use, but rigorous evidence of its benefit is lacking. This randomized controlled trial investigated whether amitriptyline provided greater pain relief or improved arm function than a placebo pill in adults with arm pain associated with repetitive use that had persisted for at least 3 months. Participants (N = 118) were randomly assigned to receive 25 mg of amitriptyline or a placebo pill for 6 weeks. The primary outcome was intensity of pain (10-point numerical rating scale) and secondary outcomes were arm symptoms, arm function, grip strength, mood, and sleep. Assessments were done at baseline, 3 and 6 weeks of treatment, and 1 month after the treatment ended. Changes in arm pain were not statistically significant. However, the amitriptyline group improved more than the placebo group in arm function (p = 0.023) and sense of well being (p = 0.034). In a longitudinal analysis, the amitriptyline group’s arm function score improved 0.45 points per week faster than placebo after adjusting for subject characteristics (p = 0.015). At the treatment’s midpoint, the amitriptyline group reported more “troublesome side-effects” than the placebo group (52.5% vs. 27.1%, p = 0.005), but this difference decreased by the end of the treatment (30.5% vs. 22.0%, p = 0.30). The most frequent side effect was drowsiness. In conclusion, this study found that low-dose amitriptyline did not significantly decrease arm pain among these participants but did significantly improve arm function and well being. Future research is needed to explore the effects of higher doses and longer duration of treatment.     

Peripheral opioid receptor blockade increases postoperative morphine demands—A randomized,double-blind,placebo-controlled trial

Experimental studies suggest that a large proportion of opioid analgesia can be mediated by peripheral opioid receptors. This trial examined the contribution of such receptors to clinical analgesia induced by intravenous morphine. We hypothesized that the selective blockade of peripheral opioid receptors by methylnaltrexone (MNX) would increase the patients’ demand for morphine to achieve satisfactory postoperative pain relief. In a double-blind, placebo-controlled, sequential 2-center trial, 50 patients undergoing knee replacement surgery were randomized (1:1) to receive either subcutaneous MNX (0.9 mg/kg) (hospital I: n = 14; hospital II: n = 11) or saline (hospital I: n = 13; hospital II: n = 12) at the end of surgery. The primary endpoint was the cumulative amount of intravenous morphine administered during the first 8 hours. Secondary endpoints were pain scores at rest and during movement (by numerical rating scale and McGill Questionnaire), vital signs, adverse side effects, and withdrawal symptoms. After MNX, demands for morphine were strongly (by about 40%) increased (hospital I: 35.31 ± 12.99 mg vs 25.51 ± 7.92 mg, P = 0.03; hospital II: 35.42 ± 11.73 mg vs 24.80 ± 7.84 mg, P = 0.02; pooled data: P < .001; means ± SD). Secondary endpoints were similar in all groups (P > .05). Thus, a significant proportion of analgesia produced by systemically administered morphine is mediated by peripheral opioid receptors. Drugs that selectively activate such receptors should have the potential to produce powerful clinical pain relief.     

Duloxetine in patients with central neuropathic pain caused by spinal cord injury or stroke: a randomized, double-blind, placebo-controlled trial

The mechanisms underlying central neuropathic pain are poorly understood. Pain inhibitory mechanisms including sertononergic and norepinephrine systems may be dysfunctional. In this randomized, double-blinded, placebo-controlled trial we evaluated the effects of duloxetine on pain relief (spontaneous pain and evoked pain), tolerability, health status, and quality of life in patients with central pain related to cerebrovascular lesions or spinal cord lesions. At baseline and eight weeks following start of treatment subjects were evaluated with standard measures of efficacy: pain intensity (primary efficacy variable), quantitative sensory testing, health status and quality of life (secondary efficacy variables). Forty-eight patients received escalating doses of either duloxetine (60 and 120 mg/day) or matching placebo capsules. In both groups, patients started with 1 capsule per day. If pain relief was insufficient, patients were titrated to a higher dose. A trend towards a decrease in mean pain score after eight weeks was observed for duloxetine treatment (p = 0.056). Duloxetine alleviated dynamic (p = 0.035) and cold allodynia (p < 0.001) significantly better than placebo. Tactile pain and pressure pain thresholds did not improve significantly. The duloxetine group showed a significant improvement for the bodily pain domain of the SF36 (p = 0.035). No significant differences were observed in the other domains of the SF36, the Pain Disability Index, and the EQ-5D. While this trial showed no significant effect on pain intensity, duloxetine revealed a biologic effect. It would be worthwhile to suspend our judgement and to perform more studies to evaluate the role of duloxetine in modulation of the symptoms of central neuropathic pain.     

Morphine consumption is not modified in patients with severe pain and classified by the DN4 score as neuropathic

Neuropathic pain has been poorly investigated in the emergency department, although it is known to be less sensitive to opioids than other forms of pain. We tested the hypothesis that morphine requirements are increased in patients having severe pain classified as neuropathic using the DN4 score. We included adult patients with acute severe pain (visual analog scale ≥ 70), assessed using the DN4 score, and treated with intravenous morphine titration (bolus of 2 or 3 mg [body weight > 60 kg] with 5-minute intervals between each bolus). Pain relief was defined as a visual analog scale 30 or less. Patients were divided into 2 groups: control group (DN4 score < 4) and neuropathic pain group (DN4 score ≥ 4). The main outcome was the total dose of morphine administered. Data are mean ± SD or median (interquartile range). Among the 239 patients included (mean age, 43 + 14 years), 35 patients (15%) had a DN4 score 4 or more. The main characteristics of the 2 groups were comparable. There were no significant differences between the 2 groups in morphine dose (0.16 + 0.09 vs 0.17 + 0.11 mg/kg, P = .32), number of boluses administered (3.5 [3-5] vs 3 [3-6], P = .97), proportion of patients with pain relief (75 vs 83%, P = .39), or morphine-related adverse effects (11% vs 3%, P = .14). In conclusion, morphine consumption was not significantly modified in patients having severe pain classified as neuropathic using the DN4 score as compared with a control group, suggesting that specific detection of neuropathic pain may not be useful in the emergency department.     

Safety and efficacy of pregabalin in patients with central post-stroke pain

Pregabalin has demonstrated efficacy in several forms of neuropathic pain, but its long-term efficacy in central post-stroke pain (CPSP) is unproven. We evaluated the efficacy and safety of pregabalin versus placebo in patients with CPSP. A 13-week, randomized, double-blind, multicenter, placebo-controlled, parallel group study of 150 to 600 mg/day pregabalin was conducted in patients aged ?18 years with CPSP. The primary efficacy endpoint was the mean pain score on the Daily Pain Rating Scale over the last 7 days on study drug up to week 12 or early termination visit. Secondary endpoints included other pain parameters and patient-reported sleep and health-related quality-of-life measures. A total of 219 patients were treated (pregabalin n = 110; placebo n = 109). A mean pain score at baseline of 6.5 in the pregabalin group and 6.3 in the placebo group reduced at endpoint to 4.9 in the pregabalin group and 5.0 in the placebo group (LS mean difference = -0.2; 95% CI = -0.7, 0.4; P = 0.578). Treatment with pregabalin resulted in significant improvements, compared with placebo, on secondary endpoints including MOS-sleep, HADS-A anxiety, and clinician global impression of change (CGIC) P < 0.05. Adverse events were more frequent with pregabalin than with placebo and caused discontinuation in 9 (8.2%) of pregabalin patients versus 4 (3.7%) of placebo patients. Although pain reductions at endpoint did not differ significantly between pregabalin and placebo, improvements in sleep, anxiety, and CGIC suggest some utility of pregabalin in the management of CPSP.     

Efficacy,safety, and tolerability of fulranumab,an anti-nerve growth factor antibody,in the treatment of patients with moderate to severe osteoarthritis pain

Nerve growth factor (NGF) is increased in chronic pain conditions. This study examined analgesic efficacy and safety of fulranumab, a fully human monoclonal anti-NGF antibody, in adults with chronic osteoarthritis pain. Patients (n = 466, intent-to-treat) were randomized to receive, in addition to their current pain therapy, subcutaneous injections in 1 of 6 parallel treatment groups: placebo (n = 78), fulranumab 1 mg (n = 77) or 3 mg (n = 79) every 4 weeks (Q4wk), 3 mg (n = 76), 6 mg (n = 78), or 10 mg (n = 78) every 8 weeks (Q8wk). Primary efficacy results showed that fulranumab significantly reduced the average pain intensity score (P ? 0.030) from baseline to week 12 compared with placebo in the 3mgQ4wk, 6mgQ8wk, and 10mgQ8wk groups. Secondary efficacy outcomes indicated that significant improvement occurred compared with placebo at week 12 on the Western Ontario and McMaster Universities Osteoarthritis Index subscales of pain, stiffness, and physical function (P < 0.040) across all fulranumab groups except 1mgQ4wk, on the Brief Pain Inventory–Short Form subscales of pain intensity (P ? 0.016) and pain interference (P ? 0.030) in the 3mgQ4wk and 10mgQ8wk groups, and on the Patient Global Assessment score (P ? 0.040) in the 3mgQ4wk, 6mgQ8wk, and 10mgQ8wk groups. The most common (?5% of patients) treatment-emergent adverse events in overall fulranumab groups during the first 12 weeks included paresthesia (7%), headache (5%), and nasopharyngitis (5%). Most neurologic-related treatment-emergent adverse events were mild or moderate and resolved at the end of week 12. Serious adverse events occurred in 3 patients, but they were not neurologically related and resolved before study completion. Fulranumab treatment resulted in statistically significant efficacy in pain measures and physical function versus placebo and was generally well tolerated.     

Effect of lingual nerve block on burning mouth syndrome (stomatodynia): A randomized crossover trial

Burning mouth syndrome (stomatodynia) is associated with changes of a neuropathic nature the main location of which, peripheral or central, remains unknown. A randomised, double-blind crossover design was used to investigate the effects of lingual nerve block on spontaneous burning pain and a possible correlation with the effects of topical clonazepam, the patient’s response to a psychological questionnaire, and the taste and heat thresholds. The spontaneous burning was measured with a visual analogue scale (VAS) just before and 15 min after injection. The decreases in VAS score after lidocaine or saline injection were not significantly different (2.7 ± 3.9 and 2.0 ± 2.6, respectively; n = 20). However, two groups of patients could be identified: in a “peripheral group” (n = 10) the VAS decrease due to lingual nerve injection was 4.3 ± 3.1 cm after lidocaine and 0.9 ± 0.3 cm after saline (p = 0.02). In a “central group” (n = 7), there were an increase in pain intensity score (−0.8 ± 2.6 cm) after lidocaine and a decrease (1.5 ± 3.0 cm) after saline (p = 0.15). An increase in the hospital anxiety and depression (HAD) score and a decreased taste sensitivity and heat pain threshold of painful oral area were seen in patients compared with age-and-sex-matched controls (p < 0.05). Topical clonazepam treatment tended to be more effective (p = 0.07) and HAD score lower (p < 0.03) in the peripheral than in the central group. These results suggest that the neuropathic disorder associated with stomatodynia may be predominantly peripheral, central or mixed depending on the individual. Topical application of clonazepam and HAD may serve as indicators of which mechanism is dominating.     

High-frequency,high-intensity transcutaneous electrical nerve stimulation as treatment of pain after surgical abortion

The aim of the study was to compare the pain-relieving effect and the time spent in the recovery ward after treatment with high-frequency, high-intensity transcutaneous electrical nerve stimulation (TENS) or intravenous (IV) conventional pharmacological treatment after surgical abortion. Two-hundred women who underwent surgical abortion and postoperatively reported a visual analogue scale (VAS) pain score ? 3 were included. The patients were randomised to TENS or conventional pharmacological treatment for their postoperative pain. The TENS treatment was given with a stimulus intensity between 20 and 60 mA during 1 min and repeated once if insufficient pain relief (VAS ? 3). In the conventional pharmacological treatment group, a maximum dose of 100 μg fentanyl was given IV. There was no difference between the groups with regard to pain relief according to the VAS pain score (TENS = VAS 1.3 vs. IV opioids = VAS 1.6; p = 0.09) upon discharge from the recovery ward. However, the patients in the TENS group spent shorter time (44 min) in the recovery ward than the conventional pharmacological treatment group (62 min; p < 0.0001). The number of patients who needed additional analgesics in the recovery ward was comparable in both groups, as was the reported VAS pain score upon leaving the hospital (TENS = 2.0 vs. conventional pharmacological treatment = 1.8, NS). These results suggest that the pain-relieving effect of TENS seems to be comparable to conventional pharmacological treatment with IV opioids. Hence, TENS may be a suitable alternative to conventional pain management with IV opioids after surgical abortion.     

Altered experimental pain perception after cerebellar infarction

Animal studies have suggested that the cerebellum, in addition to its motor functions, also has a role in pain processing and modulation, possibly because of its extensive connections with the prefrontal cortex and with brainstem regions involved in descending pain control. Consistently, human imaging studies have shown cerebellar activation in response to painful stimulation. However, it is presently not clear whether cerebellar lesions affect pain perception in humans. In the present study, we used experimental pain testing to compare acute pain perception and endogenous pain inhibition in 30 patients 1 to 11 years after cerebellar infarction and in 30 sex- and age-matched healthy control subjects. Compared to controls, patients exhibited a significantly increased pain perception in response to acute heat stimuli (44°C–48°C, average pain intensity rating for patients 3.4 ± 2.8 and for controls 1.5 ± 1.7 [on a numeric rating scale of 0–10], P < .01) and to repeated 256 mN pinprick stimuli (1.3 ± 1.9 vs 0.6 ± 1.0 [0–10], P < .05). Heat hyperalgesia in patients was more pronounced on the body side ipsilateral to the infarction. In addition, patients showed reduced offset analgesia (change in pain intensity rating: 0.0% ± 15.8% vs −16.9% ± 36.3%, P < .05) and reduced placebo analgesia (change in pain intensity rating: −1.0 ± 1.1 vs −1.8 ± 1.3 [0–10], P < .05) compared to controls. In contrast, heat and pressure pain thresholds were not significantly different between groups. These results show that, after cerebellar infarction, patients perceive heat and repeated mechanical stimuli as more painful than do healthy control subjects and have deficient activation of endogenous pain inhibitory mechanisms (offset and placebo analgesia). This suggests that the cerebellum has a previously underestimated role in human pain perception and modulation.     

Population pharmacokinetic—pharmacodynamic modeling of ketamine‐induced pain relief of chronic pain

Aims: Pharmacological treatment of chronic (neuropathic) pain is often disappointing. In order to enhance our insight in the complex interaction between analgesic drug and chronic pain relief, we performed a pharmacokinetic—pharmacodynamic (PK—PD) modeling study on the effect of S(+)‐ketamine on pain scores in Complex Regional Pain Syndrome type 1 (CRPS‐1) patients. Methods: Sixty CRPS‐1 patients were randomly allocated to received a 100‐h infusion of S(+)‐ketamine or placebo. The drug infusion rate was slowly increased from 5 mg/h (per 70 kg) to 20 mg/h based upon the effect/side effect profile. Pain scores and drug blood samples were obtained during the treatment phase and pain scores were further obtained weekly for another 11 weeks. A population PK—PD model was developed to analyze the S(+)‐ketamine‐pain data. Results: Plasma concentrations of S(+)‐ketamine and its metabolite decreased rapidly upon the termination of S(+)‐ketamine infusion. The chance for an analgesic effect from ketamine and placebo treatment was 67±10% and 23±9% (population value±SE), respectively. The pain data were well described by the PK—PD model with parameters C₅₀=10.5±4.8 ng/ml (95% ci 4.37–21.2 ng/ml) and t½ for onset/offset=10.9±4.0 days (5.3–20.5 days). Discussion: Long‐term S(+)‐ketamine treatment is effective in causing pain relief in CRPS‐1 patients with analgesia outlasting the treatment period by 50 days. These data suggest that ketamine initiated a cascade of events, including desensitization of excitatory receptor systems in the central nervous system, which persisted but slowly abated when ketamine molecules were no longer present.     

Analgesia with ibuprofen arginate versus conventional ibuprofen for patients with dysmenorrhea: a crossover trial

Background: Dysmenorrhea produces painful abdominal cramps that can disrupt the personal lives and productivity of women.Objective: The aim of this study was to compare the analgesic efficacy, including onset and duration of pain relief, peak effect, and total effect, and tolerability of ibuprofen arginate with those of conventional ibuprofen in patients with moderate to severe pain associated with primary dysmenorrhea.Methods: Patients were administered a single dose of ibuprofen arginate (200 or 400 mg), conventional ibuprofen (200 or 400 mg), or placebo during each of 5 menstrual cycles in a single-center, double-blind, randomized, double-dummy, 5-cycle, crossover study. Patients recorded their pain intensity and pain relief at regularly scheduled intervals (10, 20, 30, 40, 50, 60, and 90 minutes and 2, 3, 4, 5, and 6 hours) after taking the study medication, and all study observations were recorded in a patient diary. Pain intensity was rated using the following 4-point categoric rating scale: 0 = none, 1 = mild, 2 = moderate, and 3 = severe. Pain relief was rated on a 5-point scale as 0 = none, 1 = a little, 2 = some, 3 = a lot, and 4 = complete relief. Tolerability of ibuprofen arginate was based on a comparison of the incidence of spontaneously reported adverse events in each of the treatment groups.Results: One hundred four patients entered the study. Of these, 81.7% were white; the mean (SD) age was 27.5 (5.0) years. A total of 65.4% of patients reported moderate pain from dysmenorrhea, and the remaining 34.6% reported severe pain; 20.2% of patients did not complete the study. The median time to achieve meaningful pain relief was ∼30 minutes faster with ibuprofen arginate 400 mg than with either dose of conventional ibuprofen. Tolerability was similar across all treatments.Conclusions: In this study population of patients experiencing acute pain as a result of primary dysmenorrhea, ibuprofen arginate was associated with effective, tolerable analgesia and a more rapid onset of action than conventional ibuprofen. The faster onset of analgesia may have a role in clinical practice in treating women with dysmenorrhea. A faster onset of action may be important to women whose personal relationships, productivity, or ability to sleep is being adversely affected by pain.     

Onset of action of a lozenge containing flurbiprofen 8.75 mg: A randomized,double-blind,placebo-controlled trial with a new method for measuring onset of analgesic activity

A new onset-of-action model was utilized to distinguish the pharmacologic activity of flurbiprofen 8.75 mg delivered in a lozenge from the demulcent effect of the lozenge base. In a randomized, double-blind, placebo-controlled trial, patients with sore throat rated pain on a Sore Throat Pain Intensity Scale before taking one flurbiprofen or placebo lozenge and at frequent (2-minute) intervals over the first hour after treatment. Further ratings of the Sore Throat Pain Intensity Scale and other patient-reported outcomes (difficulty swallowing, swollen throat, pain relief) were obtained at varying intervals over 6 hours. Onset of pharmacologic activity was defined as the median time of first perceived pain reduction if a patient reported clinically meaningful (at least moderate) relief. The conventional method of comparing mean treatment responses at each time point was also implemented. Demulcent action was detected at the first 2-minute assessment. By the new method, 102 flurbiprofen-treated patients were identified as first perceiving pain relief at 12 minutes, compared with >120 minutes by 102 patients using placebo (P < 0.001). By the conventional method, mean percentage pain reduction for flurbiprofen 8.75 mg was first significantly differentiated from placebo at 26 minutes (P < 0.05). Efficacy of flurbiprofen lozenge was demonstrated for 3.5-4 hours on the 4 patient-reported outcomes (all P < 0.05 compared with placebo). There were no serious adverse events. This patient-centered onset-of-action model identifies the initiation of pain relief in patients who are definite drug responders, here demonstrating that a flurbiprofen 8.75-mg lozenge provides early relief of sore throat.     

Pain in chemotherapy-induced neuropathy – More than neuropathic?

Chemotherapy-induced neuropathy (CIN) is an adverse effect of chemotherapy. Pain in CIN might comprise neuropathic and nonneuropathic (ie, musculoskeletal) pain components, which might be characterized by pain patterns, electrophysiology, and somatosensory profiling. Included were 146 patients (100 female, 46 male; aged 56 ± 0.8 years) with CIN arising from different chemotherapy regimens. Patients were characterized clinically through nerve conduction studies (NCS) and quantitative sensory testing (QST). Questionnaires for pain (McGill) and anxiety/depression (Hospital Anxiety and Depression Scale) were supplied. Patients were followed-up after 17 days. Large- (61%) and mixed- (35%) fibre neuropathies were more frequent than small-fibre neuropathy (1.4%). The 5 major chemotherapeutic regimens impacted differently on large- but not on small-fibre function and did not predict painfulness. Chronic pain associated with CIN was reported in 41.7%. Painless and painful CIN did not differ in QST profiles or electrophysiological findings, but different somatosensory patterns were found in CIN subgroups (pain at rest [RestP], n = 25; movement-associated pain [MovP], n = 15; both pain characteristics [MovP+RestP], n = 21; or no pain [NonP], n = 85): small-fibre function (cold-detection threshold, CDT: z score: −1.46 ± 0.21, P < 0.01) was most impaired in RestP; mechanical hyperalgesia was exclusively found in MovP (z score: +0.81 ± 0.30, P < 0.05). “Anxiety” discriminated between painful and painless CIN; “CDT” and “anxiety” discriminated between patients with ongoing (RestP) and movement-associated pain (MovP) or pain components (MovP+RestP). The detrimental effect of chemotherapy on large fibres failed to differentiate painful from painless CIN. Patients stratified for musculoskeletal or neuropathic pain, however, differed in psychological and somatosensory parameters. This stratification might allow for the application of a more specific therapy.     

Pain reduction of acupoint electrical stimulation for patients with spinal surgery: a placebo-controlled study

Background

Acupoint electrical stimulation (AES) is commonly used for pain management. However, its true or placebo effect to achieve pain relief needs to be verified.

Objective

This study aimed to examine the true effect of AES to reduce postoperative pain in patients with spinal surgery receiving patient-controlled analgesia (PCA).

Method

A placebo- and sham-controlled study was conducted. Participants were randomly assigned to intervention with AES at true acupoints (the AES group, n = 30), AES at sham acupoints (the sham group, n = 30), or no intervention with AES (the control group, n = 30). Outcomes were assessed according to the amount of pain experienced and analgesics used.

Results

There were significant differences among the three groups in pain relief across time, and the occurrence of PCA button pushed and amount of analgesics used. The beneficial effects of AES were discernible when compared to the sham and the control.

Conclusions

AES at the true acupoints effectively reduced postoperative pain and analgesic usage. AES has now been implemented into healthcare and it is recommended that nurses be provided with the opportunity to earn their AES skills. More studies evaluating the effects of AES over a longer period and on pain after different surgical procedures are suggested.     

Comparison of cooling and EMLA to reduce the burning pain during capsaicin 8% patch application: A randomized,double-blind,placebo-controlled study

Topical capsaicin 8% was developed for the treatment of peripheral neuropathic pain. The pain reduction is associated with a reversible reduction of epidermal nerve fiber density (ENFD). During its application, topical capsaicin 8% provokes distinct pain. In a randomized, double-blind study analyzed with a block factorial analysis of variance, we tested whether cooling the skin would result in reliable prevention of the application pain without inhibiting reduction of ENFD. A capsaicin 8% patch was cut into 4 quarters and 2 each were applied for 1 hour on the anterior thighs of 12 healthy volunteers. A randomization scheme provided for 1 of the application sites of each thigh to be pretreated with EMLA and the other with placebo, whereas both application sites of 1 thigh, also randomly selected, were cooled by cool packs, resulting in a site temperature of 20°C during the entire treatment period. The maximum pain level given for the cooled sites (visual analogue scale [VAS] 1.3 ± 1.4) proved to be significantly lower than for the non-cooled sites (VAS 7.5 ± 1.9) (P < .0001). In contrast, there was no significant difference in application pain between the sites pretreated with EMLA or with placebo (VAS 4.1 ± 3.6 vs 4.8 ± 3.5, P = .1084). At all application sites, ENFD was significantly reduced by 8.0 ± 2.8 (ENF/mm ± SD, P < .0001), that is, 70%, with no significant differences between the sites with the different experimental conditions. In conclusion, cooling the skin to 20°C reliably prevents the pain from capsaicin 8% patch application, whereas EMLA does not. ENFD reduction is not inhibited by cooling.