Altered cortico-brainstem connectivity during spontaneous fluctuations in pain intensity in painful trigeminal neuropathy.

Chronic neuropathic pain can result from nervous system injury and can persist in the absence of external stimuli. Although ongoing pain characterizes the disorder, in many individuals, the intensity of this ongoing pain fluctuates dramatically. Previously, it was identified that functional magnetic resonance imaging (fMRI) signal covariations between the midbrain periaqueductal gray matter (PAG), rostral ventromedial medulla (RVM), and spinal trigeminal nucleus (SpV) are associated with moment-to-moment fluctuations in pain intensity in individuals with painful trigeminal neuropathy (PTN). Since this brainstem circuit is modulated by higher brain input, we sought to determine which cortical sites might be influencing this brainstem network during spontaneous fluctuations in pain intensity. Over 12 minutes, we recorded ongoing pain intensity in 24 PTN participants, and classified them as fluctuating (n=13) or stable (n=11). Using a PAG seed, we identified connections between the PAG and emotional-affective sites such as the hippocampal and posterior cingulate cortices, the sensory-discriminative posterior insula, and cognitive-affective sites such as the dorsolateral prefrontal (dlPFC) and subgenual anterior cingulate cortices that were altered dependent on spontaneous high and low pain intensity. Additionally, sliding-window functional connectivity analysis revealed that the dlPFC-PAG connection anticorrelated with perceived pain intensity over the entire 12-minute period. These findings reveal cortical systems underlying moment-to-moment changes in perceived pain in PTN, which likely cause dysregulation in the brainstem circuits previously identified, and consequently alter the appraisal of pain across time.Significance statement Whilst the intensity of an individual's chronic pain is often measured at a specific point in time, it is known that in a large proportion of individuals, pain intensity fluctuates dramatically from moment-to-moment. In individuals with chronic neuropathic pain, we found that these spontaneous pain intensity fluctuations are associated with neural function fluctuations, specifically of function reflected as neural connectivity between brainstem pain modulatory circuits and cortical regions, including the dorsolateral prefrontal and cingulate cortices. These findings raise the possibility that modulating brain regions such as the dorsolateral prefrontal cortex in individuals with fluctuating chronic pain may provide an avenue for analgesic treatment.

Altered regional brain T2 relaxation times in individuals with chronic orofacial neuropathic pain.

The neural mechanisms underlying the development and maintenance of chronic pain following nerve injury remain unclear. There is growing evidence that chronic neuropathic pain is associated with altered thalamic firing patterns, thalamocortical dysrhythmia and altered infra-slow oscillations in ascending pain pathways. Preclinical and post-mortem human studies have revealed that neuropathic pain is associated with prolonged astrocyte activation in the dorsal horn and we have suggested that this may result in altered gliotransmission, which results in altered resting neural rhythm in the ascending pain pathway. Evidence of astrocyte activation above the level of the dorsal horn in living humans is lacking and direct measurement of astrocyte activation in living humans is not possible, however, there is evidence that regional alterations in T2 relaxation times are indicative of astrogliosis. The aim of this study was to use T2 relaxometry to explore regional brain anatomy of the ascending pain pathway in individuals with chronic orofacial neuropathic pain. We found that in individuals with trigeminal neuropathic pain, decreases in T2 relaxation times occurred in the region of the spinal trigeminal nucleus and primary somatosensory cortex, as well as in higher order processing regions such as the dorsolateral prefrontal, cingulate and hippocampal/parahippocampal cortices. We speculate that these regional changes in T2 relaxation times reflect prolonged astrocyte activation, which results in altered brain rhythm and ultimately the constant perception of pain. Blocking prolonged astrocyte activation may be effective in preventing and even reversing the development of chronic pain following neural injury.

Disruption of default mode network dynamics in acute and chronic pain states.

It has been proposed that pain competes with other attention-demanding stimuli for cognitive resources, and many chronic pain patients display significant attention and mental flexibility deficits. These alterations may result from disruptions in the functioning of the default mode network (DMN) which plays a critical role in attention, memory, prospection and self-processing, and recent investigations have found alterations in DMN function in multiple chronic pain conditions. Whilst it has been proposed that these DMN alterations are a characteristic of pain that is chronic in nature, we recently reported altered oscillatory activity in the DMN during an acute, 5  minute noxious stimulus in healthy control subjects. We therefore hypothesize that altered DMN activity patterns will not be restricted to those in chronic pain but instead will also occur in healthy individuals during tonic noxious stimuli. We used functional magnetic resonance imaging to measure resting state infra-slow oscillatory activity and functional connectivity in patients with chronic orofacial pain at rest and in healthy controls during a 20-minute tonic pain stimulus. We found decreases in oscillatory activity in key regions of the DMN in patients with chronic pain, as well as in healthy controls during tonic pain in addition to changes in functional connectivity between the posterior cingulate cortex and areas of the DMN in both groups. The results show that similar alterations in DMN function occur in healthy individuals during acute noxious stimuli as well as in individuals with chronic pain. These DMN changes may reflect the presence of pain per se and may underlie alterations in attentional processes that occur in the presence of pain.

Analysis of the acute postoperative pain experience following oral surgery: identification of 'unaffected', 'disabled' and 'depressed, anxious and disabled' patient clusters.

BACKGROUND: Pain is defined as both a sensory and an emotional experience. Acute postoperative tooth extraction pain is assessed and treated as a physiological (sensory) pain while chronic pain is a biopsychosocial problem. The purpose of this study was to assess whether psychological and social changes occur in the acute pain state. METHODS: A biopsychosocial pain questionnaire was completed by 438 subjects (165 males, 273 females) with acute postoperative pain at 24 hours following the surgical extraction of teeth and compared with 273 subjects (78 males, 195 females) with chronic orofacial pain. Statistical methods used a k-means cluster analysis. RESULTS: Three clusters were identified in the acute pain group: 'unaffected', 'disabled' and 'depressed, anxious and disabled'. Psychosocial effects showed 24.8 per cent feeling 'distress/suffering' and 15.1 per cent 'sad and depressed'. Females reported higher pain intensity and more distress, depression and inadequate medication for pain relief (p < 0.001). Distress and depression were associated with higher pain intensity. The developed questionnaire had tested reliability (test-retest r = 0.89) and estimated validity. CONCLUSION: Cluster analysis showed constituent groups with a range of psychosocial effects in acute postoperative dental extraction pain and is associated with an increase in pain intensity.

Chronic orofacial pain is associated with psychological morbidity and negative personality changes: a comparison to the general population.

BACKGROUND: Chronic orofacial pain is a biopsychosocial problem. Pain description and intensity have been previously reported by the authors. This follow up study reports on the presence and severity of psychological morbidity presence and alseverity changes associated with chronic and personality changes associated with chronic orofacial pain. METHODS: A total of 415 questionnaires for psychological morbidity (238 chronic orofacial pain patients and 175 controls) and 205 responses for personality changes (105 pain patients and 100 controls) were analyzed. Demographic and status, level of education include and current work status. status, level of education and current work status. Psychological variables tested were depression, anger, fear, distress, frustration and anxiety. Pain patients indicated descriptors of their personalities 'pre-pain' and 'with pain'. RESULTS: The chronic pain group reported higher levels of 'feeling sad or miserable' p < 0.001 'feeling frustrated' p = 0.001 and 'feeling anxious, worried' p = 0.022 than the control group. Within the chronic pain group, patients unemployed due to pain or other reasons reported higher levels of 'feeling sad or miserable' and 'feeling frustrated' (p < 0.05) compared with patients engaged in full or part-time work. Negative personality changes due to pain were clearly evident with 'irritable' and 'sad' being frequently chosen words (p < 0.001). CONCLUSIONS: Patients with chronic orofacial pain suffer from negative psychological and personality changes.

Determination of testosterone in saliva and blow of bottlenose dolphins (Tursiops truncatus) using liquid chromatography-mass spectrometry.

A rapid, accurate and reproducible assay utilising high performance liquid chromatography-mass spectrometry (LC-MS) has been developed and validated for determining testosterone concentrations in saliva and blow of bottlenose dolphins. Sample preparation used solid phase extraction with specific preconditioning of cartridges. Analytes were eluted with 100% acetonitrile, dried under nitrogen and stored at -80 degrees C. Samples were reconstituted in 60% acetonitrile for LC-MS analysis. Chromatographic separation was achieved with an Alltech Macrosphere C8 stainless steel analytical column (2.1 mm x 150 mm i.d., 5 microm particle size, 300 angstroms pore size) using a 55% mobile phase B isocratic method (mobile phase A = 0.5% acetic acid; mobile phase B = 0.5% acetic acid, 90% acetonitrile). Samples were analysed in SIM at m/z 289.20 (testosterone mw 288.40) and a positive ion ESI. The limit of quantification was 0.5 ng/ml with a limit of detection of 0.2 ng/ml. The concentration curve was linear from 0.5 to 50 ng/ml (y = 0.01x + 0.0045, r(2) = 0.959, r = 0.979, p < 0.001). The R.S.D.s of intra- and inter-batch precision were less than 15% for saliva and 11% blow. Recovery of the assay for saliva was 93.0 +/- 7.9% (50 ng/ml) and 91.5 +/- 3.72% (1 ng/ml), and for blow was 83.3 +/- 6.8% (50 ng/ml) and 85.8 +/- 4.6% (1 ng/ml). Recovery of the internal standard in saliva was 73.0 +/- 14.2% and in blow was 78.63 +/- 4.29. The described assay was used to determine the presence of endogenous testosterone in saliva (9.73-23 ng/ml, n = 10) and blow (14.71-86.20 ng/ml, n = 11) samples of captive bottlenose dolphins.

High-performance liquid chromatographic determination of bradykinin in saliva: a critical review and a new method.

Because of difficulties or dubious results with previously published methodologies, a new semi-automated HPLC method with UV absorbance detection was developed and applied to the determination of bradykinin (BK) in human saliva. The new method consisted of an uncomplicated sample preparation involving the addition to saliva of an equal volume of 0.1 M orthophosphoric acid to stabilize BK, vortex-mixing, centrifugation, and separation, followed by chromatography of the supernatant phase on a C8, 150x3.9-mm (I.D.) stainless steel column. The mobile phase was composed of 19% acetonitrile/0.1% trifluoroacetic acid at flow-rate of 0.4 ml/min. Using UV detection at 220 nm, the detection limit was 1 ng/ml for the BK standard, and 7 ng/ml for the assay of endogenous salivary BK. The orthophosphoric acid initially added to the saliva allowed BK to be stabilized from enzymic degradation at 20 degrees C for 5 days and at 4 degrees C for 60 days. Assignment made to the peak with the chromatographic properties of salivary BK was confirmed by HPLC-MS with an electrospray interface. This paper presents a new method that is reproducible, reliable and allows kinetic studies of salivary BK to be performed for clinical investigations.

Determination of defensin HNP-1, HNP-2, and HNP-3 in human saliva by using LC/MS.

The mass spectral profiling of saliva by liquid chromatography mass spectrometry in relation to particular types of pain is being examined. The aim is to develop a profile that could be useful for the assessment of patients and their treatment programs, as well as identifying unknown compounds observed in saliva. Defensin human neutrophil peptide-1 (HNP-1) and defensin HNP-2 were identified and confirmed, whereas defensin HNP-3 was tentatively identified. Linear calibration range of defensin HNP-1 and HNP-2 was 0.25 to 3 microg/ml with R(2) values of > 0.99 for both. The detection limit for defensin HNP-1 and HNP-2 was estimated at 0.1 microg/ml. The healthy subjects surveyed in this study had readily measurable salivary concentrations of defensin HNP-1 (8.6 +/- SD 8.0 microg/ml) and defensin HNP-2 (5.6 +/- SD 5.2 microg/ml).

Neuropathic orofacial pain. Part 2-Diagnostic procedures, treatment guidelines and case reports.

Neuropathic orofacial pain can be difficult to diagnose because of the lack of clinical and radiographic abnormalities. Further difficulties arise if the patient exhibits significant distress and is a poor historian regarding previous diagnostic tests and treatments, such as somatosensory local anaesthetic blockade. Valuable information can be obtained by utilising the McGill Pain Questionnaire that allows the patient to choose words that describe the qualities of his/her pain in a number of important dimensions (sensory and effective). Basal pain intensity should be measured with the visual analogue scale, a simple instrument that can evaluate the efficacy of subsequent treatments. The dentist or endodontist can employ sequential analgesic blockade with topical anaesthetics and perineural administration of plain local anaesthetic to ascertain sites of neuropathology in the PNS. These can be performed in the dental chair and in a patient blinded manner. Other, more specific, tests necessitate referral to a specialist anaesthetist at a multidisciplinary pain clinic. These tests include placebo controlled lignocaine infusions for assessing neuropathic pain, and placebo controlled phentolamine infusions for sympathetically maintained pain. The treatment/management of neuropathic pain is multidisciplinary. Medication rationalisation utilises first-line antineuropathic drugs including tricyclic antidepressants such as amitriptyline and nortriptyline, and possibly an anticonvulsant such as carbamazepine, sodium valproate, or gabapentin if there are sharp, shooting qualities to the pain. Mexiletine, an antiarrhythmic agent and lignocaine analogue, may be considered following a positive patient response to a lignocaine infusion. All drugs need to be titrated to achieve maximum therapeutic effect and minimum side effects. Topical applications of capsaicin to the gingivae and oral mucosa are a simple and effective treatment in two out of three patients suffering from neuropathic orofacial pain. Temporomandibular disorder is present in two thirds of patients and should be assessed and treated with physiotherapy and where appropriate, occlusal splint therapy. Attention to the patient's psychological status is crucial and requires the skill of a clinical psychologist and/or psychiatrist with pain clinic experience. Psychological variables include distress, depression, expectations of treatment, motivation to improve, and background environmental factors. Unnecessary dental treatment to "remove the pain" with dental extractions is contraindicated and aggravates neuropathic orofacial pain.

Neuropathic orofacial pain part 1--prevalence and pathophysiology.

Neuropathic pain is defined as "pain initiated or caused by a primary lesion or dysfunction in the nervous system". Neuropathic orofacial pain has previously been known as "atypical odontalgia" (AO) and "phantom tooth pain". The patient afflicted with neuropathic oral/orofacial pain may present to the dentist with a persistent, severe pain, yet there are no clearly identifiable clinical or radiographic abnormalities. Accordingly, multiple endodontic procedures may be instigated to remove the likely anatomical source of the pain, yet the pain persists. There have been few studies and limited patient numbers investigating the condition. Two retrospective studies revealed the incidence of persistent pain following endodontic treatment to be 3-6% and 5% of patients; one author with wide experience in assessing the condition estimated its prevalence at 125,000 individuals in the USA alone. In one study, 50% of neuropathic orofacial pain patients reported persistent pain specifically following endodontic treatment. Patients predisposed to the condition may include those suffering from recurrent cluster or migraine headaches. Neuropathic pain states include postherpetic neuralgia (shingles) and phantom limb/stump pain. The aberrant developmental neurobiology leading to this pain state is complex. Neuropathic pain serves no protective function, in contrast to physiological pain that warns of noxious stimuli likely to result in tissue damage. The relevant clinical features of neuropathic pain include: (i) precipitating factors such as trauma or disease (infection), and often a delay in onset after initial injury (days-months), (ii) typical complaints such as dysaesthesias (abnormal unpleasant sensations), pain that may include burning, and paroxysmal, lancinating or sharp qualities, and pain in an area of sensory deficit, (iii) on physical examination there may be hyperalgesia, allodynia and sympathetic hyperfunction, and (iv) the pathophysiology includes deafferentation, nerve sprouting, neuroma formation and sympathetic efferent activity.

Analysis of 50 patients with atypical odontalgia. A preliminary report on pharmacological procedures for diagnosis and treatment.

Atypical odontalgia is a distressing and unusual chronic orofacial pain condition. It is often difficult to diagnose because it is associated with a lack of clinical and radiographic abnormalities. The condition is poorly understood on a pathophysiological basis, and patients often undergo repetitive and unnecessary dental procedures in attempts to alleviate pain. In this study, 50 patients diagnosed with odontalgia were evaluated by pharmacological procedures, including topical anesthetic application and phentolamine infusion. Results of these pharmacological procedures suggest that atypical odontalgia is a neuropathic pain of the oral cavity that may have a component of sympathetically maintained pain. Therapeutic trials of topical capsaicin were carried out to assess its efficacy for pain reduction. Topical capsaicin was effective in most patients.

Pain description and severity of chronic orofacial pain conditions.

A multidisciplinary pain centre study of 120 consecutive chronic orofacial pain patients assessed pain description and intensity ratings, gender differences, prevalence of concurrent conditions, and interinstrument relationships of the McGill Pain Questionnaire and visual analogue scale. Pain words chosen by patients to describe conditions were predominantly sensory words, and patients with concurrent conditions often listed words indicating a substantial affective component. Results showed pain intensity ratings of chronic orofacial pain conditions have similar or higher pain ratings when compared with other medical chronic pain conditions such as back pain, cancer pain and arthritis. There was a significantly higher female: male ratio (88:32) with gender playing an important but poorly understood causal role. The most frequent condition diagnosed was atypical facial pain (n = 40), followed by temporomandibular disorder (n = 32), atypical odontalgia (n = 29) and pathology of the orofacial region (n = 19). Temporomandibular disorder was present in 75 of the 120 subjects, as the sole pain complaint (n = 32) or as an associated secondary condition (n = 43), indicating concurrent pain conditions exist and may be related. There were significantly higher total pain scores of the McGill Pain Questionnaire in patients with multiple conditions compared with patients with a single condition. The visual analogue scale showed a significant correlation to the number of words chosen index of the McGill Pain Questionnaire for orofacial pain.

Pharmacokinetics of EMLA cream 5% application to oral mucosa.

Plasma concentrations of lidocaine and prilocaine were measured following the application of a 5% eutectic mixture of local anesthetics (EMLA) topical anesthetic cream to the oral mucosa of twelve subjects. For each subject, a total of 8 g of EMLA was occluded to 18 cm2 of buccal mucosa for 30 min. Analysis was carried out by high-pressure liquid chromatography, and results showed peak concentrations at 40 min for lidocaine and prilocaine. The maximum concentration measured in any subject was 418 ng/ml for lidocaine and 223 ng/ml for prilocaine, well below known toxic levels. No adverse local effects were observed from a 30-min application of EMLA. A follow-up pilot study assessing the clinical efficacy of EMLA for achieving sufficient analgesia for restorative procedures showed that the cream was successful in 75% of subjects tested.

Pulpal anesthesia from an application of a eutectic topical anesthetic.

A new topical anesthetic agent, EMLA cream 5%, was investigated to determine if long application times could produce a degree of pulpal anesthesia. Thirteen subjects underwent testing in a double-blind manner. Pulpal anesthesia was assessed by electrical pulp testing. After the cream was applied for 15 to 30 minutes, 92% (12/13) of subjects reported no pain to the maximum setting of the pulp tester (300 V). The results of this study suggest EMLA cream has potential application in restorative dentistry and deserves further investigation.

A clinical evaluation of three topical anaesthetic agents.

This study compared the efficacy of EMLA 5% Cream, Xylocaine 5% (lignocaine 5 per cent) and NUM (benzocaine 15 per cent, amethocaine 1.7 per cent) to a placebo in reducing the pain experience during needle insertion. In a random, double blind study three groups of twenty volunteers each had a paired topical anaesthetic/placebo placed bilaterally in the buccal sulcus of the upper premolar regions for two minutes, followed by the insertion of a standard 27 gauge needle to a depth of 5 mm. Pain experience was measured with visual analogue scales. Results showed that all three agents significantly reduced pain when compared with the placebo--EMLA (p less than 0.002); Xylocaine (p less than 0.05); NUM (p less than 0.005).