Double-blind, placebo-controlled, randomized pilot study of cerebral blood flow patterns employing SPECT imaging in dental postsurgical pain patients with and without pain relief

Radiotracers in the Diagnosis of Pain: A Mini Review

The diagnosis and understanding of pain is challenging in clinical practice. Assessing pain relies heavily on self-reporting by patients, rendering it inherently subjective. Traditional clinical imaging methods such as computed tomography and magnetic resonance imaging can only detect anatomical abnormalities, offering limited sensitivity and specificity in identifying pain-causing conditions. Radiotracers play a vital role in molecular imaging that aims to identify abnormal biological processes at the cellular level, even in apparently normal anatomical structures. Therefore, molecular imaging is an important area of research as a prospective diagnostic modality for pain-causing pathophysiology. We present a mini review of the current knowledge base regarding radiotracers for identification of pain in vivo. We also describe radiocaine, a novel positron emission tomography imaging agent for sodium channels that has shown great potential for identifying/labeling pain-producing nerves and producing an objectively measurable pain intensity signal.

Clinical effects of different virtual reality presentation content on anxiety and pain: a randomized controlled trial

Many patients are frightened of or anxious about dental treatment. We have recently reported our use of virtual reality (VR) to alleviate the fear and anxiety experienced during oral surgical procedures However, the effectiveness of VR in alleviating anxiety varies greatly between individuals. We therefore investigated whether the content of the VR presentation made any difference to its effect in alleviating anxiety, and whether it had any analgesic effect. The study subjects experienced one of two different types of VR presentation and were asked to complete a questionnaire about any changes in their anxiety during the procedure, including a visual analog scale (VAS) score. As an objective evaluation, changes in pain threshold during the VR presentation were investigated using PainVision. For those patients who experienced a presentation showing a natural landscape, the change in VAS score was - 13.3 ± 28.7 mm, whereas for those who experienced a presentation showing a video game the change was - 22.2 ± 32.1 mm, an even greater reduction. In a pain questionnaire completed by individuals who had experienced the video game presentations, approximately 70% reported that their pain had diminished. An objective evaluation of pain threshold also showed that the pain threshold of individuals increased by around 3% while experiencing the natural landscape VR presentation, but that while experiencing the video game presentation, it increased significantly by around 15% compared with baseline. These results show that the content of the presentation affected not only the rate of decrease in anxiety, but also the pain threshold.

Utility of SPECT Functional Neuroimaging of Pain

Functional neuroimaging modalities vary in spatial and temporal resolution. One major limitation of most functional neuroimaging modalities is that only neural activation taking place inside the scanner can be imaged. This limitation makes functional neuroimaging in many clinical scenarios extremely difficult or impossible. The most commonly used radiopharmaceutical in Single Photon Emission Tomography (SPECT) functional brain imaging is Technetium 99 m-labeled Ethyl Cysteinate Dimer (ECD). ECD is a lipophilic compound with unique pharmacodynamics. It crosses the blood brain barrier and has high first pass extraction by the neurons proportional to regional brain perfusion at the time of injection. It reaches peak activity in the brain 1 min after injection and is then slowly cleared from the brain following a biexponential mode. This allows for a practical imaging window of 1 or 2 h after injection. In other words, it freezes a snapshot of brain perfusion at the time of injection that is kept and can be imaged later. This unique feature allows for designing functional brain imaging studies that do not require the patient to be inside the scanner at the time of brain activation. Functional brain imaging during severe burn wound care is an example that has been extensively studied using this technique. Not only does SPECT allow for imaging of brain activity under extreme pain conditions in clinical settings, but it also allows for imaging of brain activity modulation in response to analgesic maneuvers whether pharmacologic or non-traditional such as using virtual reality analgesia. Together with its utility in extreme situations, SPECTS is also helpful in investigating brain activation under typical pain conditions such as experimental controlled pain and chronic pain syndromes.

Paracetamol is a centrally acting analgesic using mechanisms located in the periaqueductal grey

BACKGROUND AND PURPOSE

We previously demonstrated that paracetamol has to be metabolised in the brain by fatty acid amide hydrolase enzyme into AM404 (N-(4-hydroxyphenyl)-5Z,8Z,11Z,14Z-eicosatetraenamide) to activate CB₁ receptors and TRPV1 channels, which mediate its analgesic effect. However, the brain mechanisms supporting paracetamol-induced analgesia remain unknown.

EXPERIMENTAL APPROACH

The effects of paracetamol on brain function in Sprague-Dawley rats were determined by functional MRI. Levels of neurotransmitters in the periaqueductal grey (PAG) were measured using in vivo ¹ H-NMR and microdialysis. Analgesic effects of paracetamol were assessed by behavioural tests and challenged with different inhibitors, administered systemically or microinjected in the PAG.

KEY RESULTS

Paracetamol decreased the connectivity of major brain structures involved in pain processing (insula, somatosensory cortex, amygdala, hypothalamus, and the PAG). This effect was particularly prominent in the PAG, where paracetamol, after conversion to AM404, (a) modulated neuronal activity and functional connectivity, (b) promoted GABA and glutamate release, and (c) activated a TRPV1 channel-mGlu₅ receptor-PLC-DAGL-CB₁ receptor signalling cascade to exert its analgesic effects.

CONCLUSIONS AND IMPLICATIONS

The elucidation of the mechanism of action of paracetamol as an analgesic paves the way for pharmacological innovations to improve the pharmacopoeia of analgesic agents.

The Emotional Brain as a Predictor and Amplifier of Chronic Pain

Human neuroimaging studies and complementary animal experiments now identify the gross elements of the brain involved in the chronification of pain. We briefly review these advances in relation to somatic and orofacial persistent pain conditions. First, we emphasize the importance of reverse translational research for understanding chronic pain-that is, the power of deriving hypotheses directly from human brain imaging of clinical conditions that can be invasively and mechanistically studied in animal models. We then review recent findings demonstrating the importance of the emotional brain (i.e., the corticolimbic system) in the modulation of acute pain and in the prediction and amplification of chronic pain, contrasting this evidence with recent findings regarding the role of central sensitization in pain chronification, especially for orofacial pain. We next elaborate on the corticolimbic circuitry and underlying mechanisms that determine the transition to chronic pain. Given this knowledge, we advance a new mechanistic definition of chronic pain and discuss the clinical implications of this new definition as well as novel therapeutic potentials suggested by these advances.

Comparison of cerebral blood flow in oral somatic delusion in patients with and without a history of depression: a comparative case series

BACKGROUND

A significant number of patients visit dental clinics because of unusual oral sensations for which no physical cause can be found. Such patients are recognized as having oral somatic delusion (OSD). OSD may be either primary (monosymptomatic) or secondary to another disease, such as depression or cerebral infarction. Although the presenting complaints of patients with primary and secondary OSD are nearly indistinguishable, symptoms in patients with secondary OSD seem to be resistant to treatment compared with those in patients with primary OSD. Moreover, right dominant cerebral blood flow (CBF) has been reported in patients with primary OSD, but the difference in CBF between patients with primary and secondary OSD remains unclear. The aim of this study was to assess the differences in clinical characteristics and CBF distribution between patients with monosymptomatic OSD (non-depression group) and OSD in conjunction with remitted depression (depression group).

METHODS

Participants were 27 patients of a psychosomatic dentistry clinic, all diagnosed with OSD. They were categorized into either the non-depression group (17 patients) or the depression group (10 patients) on the basis of assessments by their personal medical providers. CBF was examined using single-photon emission computed tomography.

RESULTS

There was no difference in clinical presentation between the two groups. A significant right dominant asymmetry in the temporal and posterior cerebral regions was observed in both groups. In the central region, a right dominance was seen in the non-depression group, while a left dominance was seen in the depression group. Moreover, the mean regional CBF values for patients in the depression group were significantly lower in several regions (including bilateral callosomarginal, precentral, angular, temporal, posterior cerebral, pericallosal, lenticular nucleus, thalamus, and hippocampus; and right central and cerebellum) than for patients in the non-depression group.

CONCLUSION

These results suggest that the temporal and posterior cerebral regions are involved in in the pathophysiology of OSD, regardless of depression history, and that widespread CBF reduction is a characteristic of remitted depression.

A review of intranasal ketorolac tromethamine for the short-term management of moderate to moderately severe pain that requires analgesia at the opioid level

BACKGROUND

An intranasal (IN) formulation of ketorolac was recently FDA approved in adult patients for the short-term management of moderate to moderately severe pain that requires analgesia at the opioid level.

SCOPE

The aim of this paper is to provide an overview of the clinical pharmacology, pharmacokinetics, efficacy, and tolerability of IN ketorolac. Databases used for this literature search include PubMed, International Pharmaceutical Abstracts, Cochrane Library and ClinicalTrials.gov from January 1980 to January 2012. All primary papers on IN ketorolac were eligible, including pharmacologic, pharmacokinetic, clinical, outcomes, and meta-analyses. The approved product labeling was a source of information, as well as the bibliographies of published articles which were reviewed for additional pertinent literature.

FINDINGS

The search yielded six relevant studies all of which were selected for this review and included efficacy and safety trials, one pharmacokinetics study, and one preclinical study. IN ketorolac is a non-steroidal inflammatory drug that exhibits its effect mainly by inhibiting cyclo-oxygenase (COX) 1 and 2 with high affinity for COX-1. Absorption of IN ketorolac displays a median t(max) of 0.50-0.75 hours and has a t(½) of approximately 5-6 hours. Primary analyses included evaluation of morphine use and summed pain intensity difference (SPID) which was assessed using a visual analog scale. In one of the two phase III studies, the mean SPID6 score was 83.3 in the IN ketorolac group versus 37.2 in the placebo group, p = 0.007. In another phase III study, the mean SPID6 score was 117.4 in the IN ketorolac group versus 89.9 in the placebo group, p = 0.032. IN ketorolac was well-tolerated with most adverse events associated with the route of administration.

CONCLUSION

Based on the clinical trials reviewed, IN ketorolac was associated with significant pain reduction in patients with various post-operative procedures, with good tolerability.

Acetaminophen differentially enhances social behavior and cortical cannabinoid levels in inbred mice

Supratherapeutic doses of the analgesic acetaminophen (paracetomol) are reported to promote social behavior in Swiss mice. However, we hypothesized that it might not promote sociability in other strains due to cannabinoid CB(1) receptor-mediated inhibition of serotonin (5-HT) transmission in the frontal cortex. We examined the effects of acetaminophen on social and repetitive behaviors in comparison to a cannabinoid agonist, WIN 55,212-2, in two strains of socially-deficient mice, BTBR and 129S1/SvImJ (129S). Acetaminophen (100mg/kg) enhanced social interactions in BTBR, and social novelty preference and marble burying in 129S at serum levels of ≥70 ng/ml. Following acetaminophen injection or sociability testing, anandamide (AEA) increased in BTBR frontal cortex, while behavior testing increased 2-arachidonyl glycerol (2-AG) levels in 129S frontal cortex. In contrast, WIN 55,212-2 (0.1mg/kg) did not enhance sociability. Further, we expected CB(1)-deficient (+/-) mice to be less social than wild-type, but instead found similar sociability. Given strain differences in endocannabinoid response to acetaminophen, we compared cortical CB(1) and 5-HT(1A) receptor density and function relative to sociable C57BL/6 mice. CB(1) receptor saturation binding (Bmax=958±117 fmol/mg protein), and affinity for [(3)H] CP55,940 (K(D)=3±0.8 nM) was similar in frontal cortex among strains. CP55,940-stimulated [(35)S] GTPγS binding in cingulate cortex was 136±12, 156±22, and 75±9% above basal in BTBR, 129S and C57BL/6 mice. The acetaminophen metabolite para-aminophenol (1 μM) failed to stimulate [(35)S] GTPγS binding. Hence, it appears that other indirect actions of acetaminophen, including 5-HT receptor agonism, may underlie its sociability promoting properties outweighing any CB(1) mediated suppression by locally-elevated endocannabinoids in these mice.

Posterior insular molecular changes in myofascial pain

Temporomandibular disorders (TMD) include craniocervical pain conditions with unclear etiologies. Central changes are suspected; however, few neuroimaging studies of TMD exist. Single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) was used before and after pressure-pain testing to assess glutamate (Glu), glutamine (Gln), N-acetylaspartate (NAA), and choline (Cho) levels in the right and left posterior insulae of 11 individuals with myofascial TMD and 11 matched control individuals. Glu levels were significantly lower in all individuals after pain testing. Among those with TMD, left-insular Gln levels were related to reported pain, left posterior insular NAA and Cho levels were significantly higher at baseline than in control individuals, and NAA levels were significantly correlated with pain-symptom duration, suggesting adaptive changes. The results suggest that significant central cellular and molecular changes can occur in individuals with TMD.