Volume 4, Issue 1

Background Neuropathic pain remains a significant challenge with unsatisfactory therapeutic options. Its pathogenesis may involve the neuropathic triad of neuronal, glial and immune cells. Communication between these cells is possibly perpetuated by mitogen-activated protein kinase (MAPK)-signaling. For several years, we successfully treated a rectal cancer patient with the epithelial growth factor receptor (EGFR)-inhibitor cetuximab, for debilitating neuropathic pain due to progressive malignant invasion of the sacral plexus. Here, we report the effect of treatment with various EGFR-inhibitors in five additional patients with severe and long-standing, therapy-resistant neuropathic pain. Methods All patients had well-documented neuropathic pain syndromes with the following etiologies: inflammatory polyneuropathy, complex regional pain syndrome type 1, radiculopathy after failed back surgery, malignant invasion of the sacral plexus by bladder cancer, and phantom limb pain. All patients were given intravenous (extracellular) EGFR-inhibitors (cetuximab, panitumumab) initially, and switched to oral (intracellular) agents (gefitinib, erlotinib) after an analgesic effect was obtained. Results Four of the five patients responded, all within 24h of intravenous administration, with a mean decrease in worst pain from 9 to 1 on a 10-point scale. All four EGFR-inhibitors were effective. The clinical courses, including patient-reported pain relief, are prospectively documented with 78–219 days follow-up for those who responded to treatment. Toxicities were transient and manageable. Conclusions/implications EGFR-inhibition resulted in dramatic relief of neuropathic pain. A plausible biological explanation involves the interruption of MAPK-signaling. The role of EGFR-inhibition as a target for the treatment of neuropathic pain appears promising and warrants investigation.

Background and purpose Conditioned pain modulation (CPM) is a testing paradigm representing features of diffuse noxious inhibitory control. There is large diversity in the paradigms applied to induce CPM, and the consistency in CPM responses assessed by different paradigms is largely unknown. We aimed to characterize and explore the associations between the CPM responses assessed by different paradigms in the same cohort. Methods Thirty-three healthy middle-aged subjects underwent six CPM paradigms. The ‘test-stimuli’, consisted of thermal and mechanical modalities, using pain thresholds, suprathreshold pain and temporal summation types of measurements. The ‘conditioning-stimulus’ consisted of a contact heat stimulus applied to the thener of the left hand for 60s at an intensity of 46.5°C. Results Large variability was observed among the responses to the different CPM paradigms. Surprisingly, no correlations were found between the various CPM responses. Conclusions The variability in the CPM responses may suggest that the capacity of pain modulation is a multifaceted trait, whose expression varies with the application of different CPM paradigms. Implications Considering that CPM responses may represent different processes when assessed by different paradigms, we encourage the use of more than one CPM paradigm.

Aim To evaluate the analgesic efficacy of AZD1940, a novel peripherally acting cannabinoid CB 1 /CB 2 receptor agonist, in patients undergoing third molar surgical removal. Methods This was a randomized, double-blind, placebo-controlled study in patients scheduled for surgical removal of an impacted lower third molar. Patients received a single oral dose of 800 μg AZD1940, 500 mg naproxen or placebo 1.5 h before surgery. The dose of 800 μg AZD1940 was selected based on earlier data from a single dose study in man, in which it was identified as the highest well tolerated dose. Ongoing post-operative pain (primary variable) and pain on jaw movement were assessed on a visual analog scale (VAS, 0-100 mm) from 0 to 8h postoperatively, deriving the area under the curve of ongoing pain (VAS AUC 0–8h ), and of pain on jaw movement (VAS JM AUC 0–8h ). The time to requesting rescue medication (acetaminophen) was recorded. Subjective cannabinoid effects were assessed by the visual analog mood scale (VAMS). Results In total, 151 patients were randomized to AZD1940 ( n = 61), placebo ( n = 59) or naproxen ( n = 31). There was no statistically significant difference in pain VAS AUC 0–8h or in VAS JM AUC 0–8h between AZD1940 and placebo. Naproxen significantly reduced both pain VAS AUC 0–8h and VAS JM AUC 0–8h as compared with placebo ( p < 0.0001 for both). Significantly fewer patients on naproxen requested rescue medication and the duration of time to rescue was greater, as compared with placebo, whereas there were no significant differences between AZD1940 and placebo in these outcome variables. Statistically significant increases in VAMS items “sedated” and “high” were observed after AZD1940 compared with placebo. The increases in VAMS were numerically small compared with previous findings with a centrally acting cannabinoid. The most commonly observed adverse events (AE) on treatment with AZD1940 were postural dizziness (80% of subjects), nausea (26%), hypotension (21%) and headache (13%), most AE being mild to moderate. Conclusion The CB 1 /CB 2 receptor agonist AZD1940 did not reduce post-operative pain after lower third molar surgical removal at doses exerting subjective cannabinoid effects. Implications Activation of peripheral CB 1 /CB 2 receptors per se is probably of less clinical relevance for the treatment of acute nociceptive pain in man.

Background and aim Physicians’ attitudes predict clinical decision making and treatment choices, but the association between attitudes and behaviour is complex. Treatment guidelines for non-specific low back pain (LBP) include recommendations of early assessment of psychosocial risk factors forchronic pain, patient education and reassurance. Implication of these principles is demanding, and many patients are not referred for appropriate treatments due to a lack of systematic screening of psychosocial risk factors for chronic pain. Even though health care providers recognise the need for psychosocial assessment in LBP, psychosocial issues are seldom raised in acute settings. The aim of this study is to evaluate how physicians’ attitudes towards assessing psychological issues of LBP patients are associated with their treatment practice, and to assess if their clinical actions follow current treatment guidelines. Methods The study was amixed methods study of primary care physicians ( n = 55) in Finland. Physicians’ attitudes were measured with a psychological subscale of attitudes to back pain scales for musculoskeletal practitioners (ABS-mp). Treatment practice of LBP was evaluated by as king physicians to describe a typical LBP treatment process and by asking them to solve a LBP patient case. Members of the research team individually evaluated the degree to which psychosocial issues were taken into account in the treatment process and in the patient case answer. Qualitative and quantitative data were combined to examine the role of attitudes in the treatment of LBP. Results The attitudes of physicians were generally psychologically oriented. Physicians who addressed to psychosocial issues in their treatment practice were more psychologically oriented in their attitudes than physicians who did not consider psychosocial issues. Only 20% of physicians mentioned psychosocial issues as being a part of the LBP patient’s typical treatment process, while 87% of physicians paid attention to psychosocial issues in the LBP patient case. On the level of the treatment process, radiological investigations were over-represented and pain assessment, patient information and reassurance infrequently performed when compared to LBP guidelines. Conclusions Although primary care physicians were generally psychosocially oriented in their attitudes on LBP, psychological issues were inconsistently brought up in their reported clinical behaviour. Physicians recognised the need to assess psychosocial factors. Those who were psychologically oriented in their attitudes were more inclined to take psychosocial issues into account. However on a process level, evaluation and treatment of LBP featured biomechanical principles. LBP guidelines were only partially followed. Implications Clinical behaviour of physicians in the treatment of LBP is complex and only partly explained by attitudes.

Aims Pain in response to innocuous cold stimulation (cold allodynia) is a common symptom in patients with neuropathic pain. Cold allodynia is difficult to treat and its mechanisms are poorly understood. Several transient receptor potential (TRP) channels have been shown to be the molecular sensors for cold stimulation in a temperature-dependent manner, but the contribution of various TRP channels in mediating cold allodynia in neuropathic pain is unclear. We have previously shown that spinally injured rats developed neuropathic pain-like behaviors, including marked cold allodynia. We now assessed the role of TRP channels in mediating cold allodynia in rats after ischemic spinal cord injury. Methods Methods: Spinal cord injury was produced using a photochemical method. The mechanical allodynia was assessed by examining the vocalization thresholds to graded mechanical touch/pressure applied with von Frey hairs. Temperature controlled cold stimulation was produced by a Peltier thermode (active surface 25 mm × 50 mm) connected to a MSA Thermal Simulator (Somedic, Sweden) with baseline temperature of 32 °C. The rate of temperature change was 0.5 °C/s. The temperature required to elicit cold allodynia was examined. The responses of the rats to topical application of icilin or menthol, agonists of transient receptor potential melastain 8 (TRPM8), were also studied. Results Normal rats did not exhibit nociceptive responses to cooling stimulation to the trunk and back area (minimal temperature +6°C) and they also did not react aversively to topical application of icilin or menthol. After spinal cord injury, the rats developed mechanical allodynia at the trunk and back just rostral to the dermatome of the injured spinal segments. In the same area, rats exhibited significant nociceptive responses to cooling from day 1 after injury, lasting for at least 70 days which is the longest time of observation. For the first two weeks after injury, the majority of spinally injured rats had a nociceptive response to cooling above 17°C. At day 70, about 50% of rats responded to cooling above 17 °C. Topical application of 400 μM icilin or 4mM menthol also elicited pain-like responses in spinally injured rats and these two cold mimetics also significantly exacerbated existing mechanical allodynia. Conclusion Our results showed that activation of the TRPM8 channel by menthol or icilin triggers allodynia in spinally injured rats and increases, rather than decreases, mechanical allodynia. TRPM8 channels which respond to cooling above 17 ° C may be involved at least in part in mediating cold allodynia in the rat model of neuropathic spinal cord injury pain. Implications The work introduced a method of quantitative testings of responses of rats to cold stimulation and may contribute to the understanding of mechanisms of cold allodynia after injury to the nervous system.

Background and purpose The UV-B model is an established pain model of different types of hyperalgesia in animal and human pain research. Beside the skin region of the sunburn in human volunteers pinprick hyperalgesia has been described in a large zone of non-inflamed skin adjacent to the sunburn. However, there are opposing results on the existence of pinprick hyperalgesia and most notably a controversial discussion is still on-going whether this mechanical hyperalgesia in the undamaged tissue adjacent to and at some distance from the site of inflammation is of peripheral or central origin. We therefore addressed this in our study by hypothesising that pinprick hyperalgesia around a circular spot of UV-B inflamed skin is not reduced by a superficial local anaesthetic block and therefore underlies centrally mediated mechanisms. Methods This exploratory study was conducted in a prospective, controlled, randomised, single-blinded fashion in relation to the study hypothesis in 12 healthy volunteers. Before circular irradiation with UV-B light (3-times the individual minimal erythema dose at both thighs), a strip of continuous intradermal local anaesthetic block with lidocaine 2% was established via two single plasmaphoresis hollow fibres. These were positioned perpendicular to one thigh overlapping on the midline of the leg at the distal part of the planned irradiation site, and compared with the contralateral control side without anaesthetic block. The local anaesthetic block was established and then maintained via a syringe pump. The area of pinprick hyperalgesia was measured by pricking on a large skin surface including 360° around the circular irradiation site. This was done with a slightly painful pin (256 mN) until 8h after irradiation. Primary outcome was the area of pinprick hyperalgesia in the skin adjacent to the sunburn at 8h. Results Large areas of mechanical hyperalgesia to pinprick surrounding the adjacent skin of the sunburn developed on both sides after 8h without any significant difference between the side of the anaesthetic strip showing an area of 72.6±39.7 cm 2 (mean±SD) and the control side (59.1±20.1 cm 2 ); p = 0.24. Moreover, mechanical hyperalgesia to various pin stimuli of different strength was unchanged by the anaesthetic block. Conclusion This trial provides evidence that the development of mechanical hyperalgesia surrounding an experimental sunburn was not influenced by continuous peripheral afferent blockade with local anaesthetic at 8h after UV-B irradiation. Our data support the hypothesis that in the UV-B model peripheral nociceptive afferent input of inflamed skin may enhance central hypersensitivity of mechanosensitive nociceptors in a larger receptive field far beyond the inflamed skin. Furthermore, these findings are in line with other pain models demonstrating comparable central hypersensitivity around the site of injury. Implications As for other pain models this finding provides further evidence that the UV-B model offers secondary mechanical hyperalgesia in addition to its known primary hyperalgesia. Consequently, this is a further validation for the utilisation of the UV-B model in human pain research.

Background and aims NXN-188 is a combined neuronal nitric oxide synthase (nNOS) inhibitor and 5HT-1B/1D receptor agonist which has previously shown efficacy in the acute treatment of migraine. Nitric oxide (NO) is involved in the pathogenesis of migraine pain and is formed after cortical spreading depression. Therefore NXN-188 could perhaps prevent the development of the headache phase in migraine with aura if taken during the aura. The aims of the present study were to evaluate the efficacy and safety of 600mg NXN-188 in the acute treatment of migraine when dosed during the aura. Methods A single-centre, randomized, double-blind, placebo-controlled, two-way crossover trial. The study medication was taken during the aura and the patients kept a study diary for 48h post-dose. Results Of 615 patients screened, 50 patients were included in the study and randomized. Only 18 patients completed both treatments in compliance with the study procedures. 22% of patients reported freedom of headache at 2h after intake of NXN-188 compared with only 11% of patients after placebo. Conclusions The dual-action drug NXN-188 with 5HT-1B/1D agonism and nNOS inhibition, taken orally during the aura phase did not have a statistically substantial effect on migraine headache in this study. This study was limited by a high drop-out rate and small sample of included patients who were able to complete the cross-over protocol. Therefore, efficacy of the treatment cannot be refuted with certainty. Implications This study illustrates the difficulties of doing well controlled studies in migraine patients with aura. nNOS inhibition is expected to be effective mostly in the aura phase, i.e. the oral administration may have had too slow pharmacokinetics to have effect. Parenteral administration may overcome this obstacle. 5HT-1B/1D agonism is not effective when dosed during migraine aura. Repeated dosing of the NXN-188 during and immediately following the aura may have exploited more the dualaction. The high drop-out rate may be reduced in future studies by having the patients familiarize themselves with the study procedure by filling out the attack report form while treating one attack with their own medication before entering the trial. A parallel group comparison may be a more effective trial design for treatment during an aura.