Towards a pain treatment based on the identification of the pain-generating mechanisms?

[Specificities of orofacial neuropathic pain]

Head pain and notably orofacial pain differs from spinal pain on pathophysiological, clinical, therapeutic and prognostic levels. Its high prevalence, important impact on quality of life and significant socio-economical burden justify specific study of such type of pain. Among them, neuropathic orofacial pain resulting from disease or trauma of the trigeminal nervous system is among the most difficult types of pain to diagnose and to treat. Deciphering of underlying peripheral and central mechanisms has allowed numerous conceptual, clinical and therapeutic advances, notably the role of neural and non neural cell types, such as glia, immunocytes, vascular endothelial cells or the role of trigeminal sensory complex neural circuitry reconfiguration in the development of post-traumatic trigeminal neuropathic pain. Cellular interactions within the trigeminal ganglion, allowing a better understanding of several painful dental, ocular or cephalalgic comorbidities, are also described.

Orofacial Pain and Dentistry Management: Guidelines for a More Comprehensive Evidence-Based Approach

Orofacial pain represents one of the most common health problems that negatively affects the activities of daily living. However, the mechanisms underlying these conditions are still unclear, and their comprehensive management is often lacking. Moreover, even if pain is a common symptom in dentistry, differential diagnostic procedures are needed to exclude other pain origins. Misinterpretation of the pain origin, in fact, can lead to misdiagnosis and to subsequent mismanagement. Pain in the orofacial area is the most common reason for patients to visit the dentist, but this area is complex, and the pain could be associated with the hard and soft tissues of the head, face, oral cavity, or to a dysfunction of the nervous system. Considering that the origins of orofacial pain can be many and varied, a thorough assessment of the situation is necessary to enable the most appropriate diagnostic pathway to be followed to achieve optimal clinical and therapeutic management.

Methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system: a systematic review

ABSTRACT

Mechanism-based classification of pain has been advocated widely to aid tailoring of interventions for individuals experiencing persistent musculoskeletal pain. Three pain mechanism categories (PMCs) are defined by the International Association for the Study of Pain: nociceptive, neuropathic, and nociplastic pain. Discrimination between them remains challenging. This study aimed to build on a framework developed to converge the diverse literature of PMCs to systematically review methods purported to discriminate between them; synthesise and thematically analyse these methods to identify the convergence and divergence of opinion; and report validation, psychometric properties, and strengths/weaknesses of these methods. The search strategy identified articles discussing methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system. Studies that assessed the validity of methods to discriminate between categories were assessed for quality. Extraction and thematic analysis were undertaken on 184 articles. Data synthesis identified 200 methods in 5 themes: clinical examination, quantitative sensory testing, imaging, diagnostic and laboratory testing, and pain-type questionnaires. Few methods have been validated for discrimination between PMCs. There was general convergence but some disagreement regarding findings that discriminate between PMCs. A combination of features and methods, rather than a single method, was generally recommended to discriminate between PMCs. Two major limitations were identified: an overlap of findings of methods between categories due to mixed presentations and many methods considered discrimination between 2 PMCs but not others. The results of this review provide a foundation to refine methods to differentiate mechanisms for musculoskeletal pain.

Recent advances in our understanding of the organization of dorsal horn neuron populations and their contribution to cutaneous mechanical allodynia

The dorsal horns of the spinal cord and the trigeminal nuclei in the brainstem contain neuron populations that are critical to process sensory information. Neurons in these areas are highly heterogeneous in their morphology, molecular phenotype and intrinsic properties, making it difficult to identify functionally distinct cell populations, and to determine how these are engaged in pathophysiological conditions. There is a growing consensus concerning the classification of neuron populations, based on transcriptomic and transductomic analyses of the dorsal horn. These approaches have led to the discovery of several molecularly defined cell types that have been implicated in cutaneous mechanical allodynia, a highly prevalent and difficult-to-treat symptom of chronic pain, in which touch becomes painful. The main objective of this review is to provide a contemporary view of dorsal horn neuronal populations, and describe recent advances in our understanding of on how they participate in cutaneous mechanical allodynia.

Comparison of tramadol and lornoxicam in intravenous regional anesthesia: a randomized controlled trial

BACKGROUND AND OBJECTIVES

Tourniquet pain is one of the major obstacles for intravenous regional anesthesia. We aimed to compare tramadol and lornoxicam used in intravenous regional anesthesia as regards their effects on the quality of anesthesia, tourniquet pain and postoperative pain as well.

METHODS

After the ethics committee approval 51 patients of ASA physical status I-II aged 18-65 years were enrolled. The patients were divided into three groups. Group P (n = 17) received 3mg/kg 0.5% prilocaine; group PT (n = 17) 3mg/kg 0.5% prilocaine + 2 mL (100mg) tramadol and group PL (n = 17) 3mg/kg 0.5% prilocaine + 2 mL (8 mg) lornoxicam for intravenous regional anesthesia. Sensory and motor block onset and recovery times were noted, as well as tourniquet pains and postoperative analgesic consumptions.

RESULTS

Sensory block onset times in the groups PT and PL were shorter, whereas the corresponding recovery times were longer than those in the group P. Motor block onset times in the groups PT and PL were shorter than that in the group P, whereas recovery time in the group PL was longer than those in the groups P and PT. Tourniquet pain onset time was shortest in the group P and longest in the group PL. There was no difference regarding tourniquet pain among the groups. Group PL displayed the lowest analgesic consumption postoperatively.

CONCLUSION

Adding tramadol and lornoxicam to prilocaine for intravenous regional anesthesia produces favorable effects on sensory and motor blockade. Postoperative analgesic consumption can be decreased by adding tramadol and lornoxicam to prilocaine in intravenous regional anesthesia.

[Comparison of tramadol and lornoxicam in intravenous regional anesthesia: a randomized controlled trial]

BACKGROUND AND OBJECTIVES

Tourniquet pain is one of the major obstacles for intravenous regional anesthesia. We aimed to compare tramadol and lornoxicam used in intravenous regional anesthesia as regards their effects on the quality of anesthesia, tourniquet pain and postoperative pain as well.

METHODS

After the ethics committee approval 51 patients of ASA physical status I-II aged 18-65 years were enrolled. The patients were divided into three groups. Group P (n=17) received 3mg/kg 0.5% prilocaine; group PT (n=17) 3mg/kg 0.5% prilocaine+2mL (100mg) tramadol and group PL (n=17) 3mg/kg 0.5% prilocaine+2mL (8mg) lornoxicam for intravenous regional anesthesia. Sensory and motor block onset and recovery times were noted, as well as tourniquet pains and postoperative analgesic consumptions.

RESULTS

Sensory block onset times in the groups PT and PL were shorter, whereas the corresponding recovery times were longer than those in the group P. Motor block onset times in the groups PT and PL were shorter than that in the group P, whereas recovery time in the group PL was longer than those in the groups P and PT. Tourniquet pain onset time was shortest in the group P and longest in the group PL. There was no difference regarding tourniquet pain among the groups. Group PL displayed the lowest analgesic consumption postoperatively.

CONCLUSION

Adding tramadol and lornoxicam to prilocaine for intravenous regional anesthesia produces favorable effects on sensory and motor blockade. Postoperative analgesic consumption can be decreased by adding tramadol and lornoxicam to prilocaine in intravenous regional anesthesia.

The Analgesic Effect of Dexketoprofen When Added to Lidocaine for Intravenous Regional Anaesthesia: A Prospective, Randomized, Placebo-Controlled Study

This prospective, randomized, placebo-controlled study evaluated the effects of dexketoprofen as an adjunct to lidocaine in intravenous regional anaesthesia (IVRA) or as a supplemental intravenous (i.v.) analgesic. Patients scheduled for elective hand or forearm soft-tissue surgery were randomly divided into three groups. All 45 patients received 0.5% lidocaine as IVRA. Dexketoprofen was given either i.v. or added into the IVRA solution and the control group received an equal volume of saline both i.v. and as part of the IVRA. The times of sensory and motor block onset, recovery time and postoperative analgesic consumption were recorded. Compared with controls, the addition of dexketoprofen to the IVRA solution resulted in more rapid onset of sensory and motor block, longer recovery time, decreased intra- and postoperative pain scores and decreased paracetamol use. It is concluded that coadministration of dexketoprofen with lidocaine in IVRA improves anaesthetic block and decreases postoperative analgesic requirements.

The reliability of clinical judgments and criteria associated with mechanisms-based classifications of pain in patients with low back pain disorders: a preliminary reliability study

Mechanisms-based classifications of pain have been advocated for their potential to aid understanding of clinical presentations of pain and improve clinical outcomes. However, the reliability of mechanisms-based classifications of pain and the clinical criteria upon which such classifications are based are not known. The purpose of this investigation was to assess the inter- and intra-examiner reliability of clinical judgments associated with: (i) mechanisms-based classifications of pain; and (ii) the identification and interpretation of individual symptoms and signs from a Delphi-derived expert consensus list of clinical criteria associated with mechanisms-based classifications of pain in patients with low back (±leg) pain disorders. The inter- and intra-examiner reliability of an examination protocol performed by two physiotherapists on two separate cohorts of 40 patients was assessed. Data were analysed using kappa and percentage of agreement values. Inter- and intra-examiner agreement associated with clinicians' mechanisms-based classifications of low back (±leg) pain was 'substantial' (kappa  = 0.77; 95% confidence interval (CI): 0.57-0.96; % agreement  = 87.5) and 'almost perfect' (kappa  = 0.96; 95% CI: 0.92-1.00; % agreement = 92.5), respectively. Sixty-eight and 95% of items on the clinical criteria checklist demonstrated clinically acceptable (kappa ⩾ 0.61 or % agreement ⩾ 80%) inter- and intra-examiner reliability, respectively. The results of this study provide preliminary evidence supporting the reliability of clinical judgments associated with mechanisms-based classifications of pain in patients with low back (±leg) pain disorders. The reliability of mechanisms-based classifications of pain should be investigated using larger samples of patients and multiple independent examiners.

The analgesic effect of lornoxicam when added to lidocaine for intravenous regional anaesthesia

BACKGROUND

The aim of the study was to evaluate the effect of lornoxicam (L) on sensory and motor block onset time, tourniquet pain, and postoperative analgesia, when added to lidocaine in intravenous regional anaesthesia (IVRA).

METHODS

Forty-five patients undergoing hand surgery were randomly and blindly divided into three groups as to receive either i.v. saline and IVRA with lidocaine 0.5% (Control group, n=15), i.v. saline and IVRA lidocaine 0.5% with lornoxicam (L-IVRA group, n=15), or intravenous lornoxicam and IVRA lidocaine 0.5% (L-IV group, n=15). Sensory and motor blocks onset time, and tourniquet pain was measured after tourniquet application at 5, 10, 20, and 30 min, and analgesic use were recorded during operation. After the tourniquet deflation, at 1, 30 min, and 2, 4 h, visual analogue scales score, the time to first analgesic requirement, total analgesic consumption in first 24 h, and side effects were noted.

RESULTS

Sensory and motor block onset times were shorter and the recovery time prolonged in the Group L-IVRA compared with the other group (P=0.001). A decreased tourniquet pain, a prolonged time first analgesic requirement [229 (85) min vs 28 (20) and 95 (24) min, P=0.0038) and less postoperative analgesic requirements during 24 h were found in Group L-IVRA compared with the other groups (P<0.05).

CONCLUSIONS

The addition of lornoxicam to lidocaine for intravenous regional anaesthesia shortens the onset of sensory and motor block, decreases tourniquet pain and improves postoperative analgesia without causing any side effect.

Patterns of P-glycoprotein activity in the nervous system during vincristine-induced neuropathy in rats

Vincristine (VCT) is a neurotoxic agent and also a substrate of multidrug resistance (MDR) transporters such as P-glycoprotein (P-gp) and MDR-associated proteins 1 and 2 (MRP1 and MRP2). These proteins are expressed in the central and peripheral nervous systems (CNS and PNS) and normally protect these structures against the harmful effects of VCT. The aim of this study was to elucidate the paradoxical relation between the MDR transporters and the VCT neurotoxicity. With a validated rat model of VCT-induced neuropathy, (1) the expressions of mdr1a (P-gp), mdr1b (P-gp), mrp1 (MRP1), and mrp2 (MRP2) genes were assessed by quantitative real-time polymerase chain reaction, and (2) the transporter activity was monitored using a radioactive tracer, (99m)Tc-sestamibi, in the CNS and PNS. The results showed higher expression of mdr1a and mdr1b genes (x3 and x35, respectively) in the brain than in the spinal ganglia in both control and treated animals. Transporter activity was higher (x10) in the CNS than in the PNS. Hence, P-gp protection may be lower in the PNS than in the CNS, and this may be responsible for the peripheral neurotoxicity of P-gp substrates. VCT treatment increased expression of the mdr1a gene in the CNS and PNS (both x1.7), mrp1 gene in the PNS (x1.7), and transporter activity in both the CNS and the PNS (x4 and x8, respectively). This transporter induction may induce adverse effects when analgesic drugs are administered to treat neuropathic pain.

[Neurobiology of trigeminal pain]

The brainstem trigeminal complex integrates somatosensory inputs from orofacial areas and meninges. Recent studies have shown the existence of a double representation of pain within the brainstem, at the level of both caudalis and oralis subnuclei. Noxious messages are mainly conveyed by C-fibers that activate the subnucleus caudalis neurons. These neurons in turn activate the subnucleus oralis whose neurons share similar features with the deep spinal dorsal horn neurons. In contrast with the nearness of the laminar organization of the dorsal horn, the vertical organization of the trigeminal complex offers an easier access for the study of segmental mechanisms of nociceptive processing. This model allowed us to show the existence of subtle NMDA-related mechanisms of segmental nocious processing. The trigeminal complex conveys nociceptive messages to several brainstem and thalamic relays that activate a number of cortical areas responsible for pain sensations and reactions. Cortical processing is sustained by reciprocal interactions with thalamic areas and also by a direct modulation of their pre-thalamic relays. The dysfunction of these multiple modulatory mechanisms probably plays a key role in the pathophysiology of chronic trigeminal pain.