Quantitative sensory testing

Effect of 1.5% Topical Diclofenac on Clinical Neuropathic Pain

Background:

Neuropathic pain is a condition resulting from injury to the peripheral and/or central nervous system. Despite extensive research over the last several decades, neuropathic pain remains difficult to manage.

Methods:

The authors conducted a randomized, placebo-controlled, double-blinded, and crossover clinical trial to examine the effect of 1.5% topical diclofenac (TD) on neuropathic pain. The authors hypothesized that 1.5% TD would reduce the visual pain score and improve both quantitative sensory testing and functional status in subjects with neuropathic pain. The authors recruited subjects with postherpetic neuralgia and complex regional pain syndrome. The primary outcome was subject’s visual pain score.

Results:

Twenty-eight subjects completed the study (12 male and 16 female) with the mean age of 48.8 yr. After 2 weeks of topical application, subjects in 1.5% TD group showed lower overall visual pain score compared with placebo group (4.9 [1.9] vs. 5.6 [2.1], difference: 0.8; 95% CI, 0.1 to 1.3; P = 0.04) as well as decreased burning pain (2.9 [2.6] vs. 4.3 [2.8], difference, 1.4; 95% CI, 0.2 to 2.6; P = 0.01). There were no statistical differences in constant pain, shooting pain, or hypersensitivity over the painful area between the groups. This self-reported improvement of pain was corroborated by the decreased pain summation detected by quantitative sensory testing. There were no statistically significant changes in functional status in these subjects. There were no complications in both groups.

Conclusion:

The findings indicate that 1.5% TD may serve as an effective treatment option for patients with neuropathic pain from postherpetic neuralgia and complex regional pain syndrome.

Effects of Spinal Cord Stimulation on Pain Thresholds and Sensory Perceptions in Chronic Pain Patients

OBJECTIVE

Spinal cord stimulation (SCS) has been in clinical use for nearly four decades. In earliest observations, researchers found a significant increase in pain threshold during SCS therapy without changes associated with touch, position, and vibration sensation. Subsequent studies yielded diverse results regarding how SCS impacts pain and other sensory thresholds. This pilot study uses quantitative sensory testing (QST) to objectively quantify the impact of SCS on warm sensation, heat pain threshold, and heat pain tolerance.

MATERIALS AND METHODS

Nineteen subjects with an indwelling SCS device for chronic pain were subjected to QST with heat stimuli. QST was performed on an area of pain covered with SCS-induced paresthesia and an area without pain and without paresthesia, while the SCS was turned off and on. The temperature at which the patient detected warm sensation, heat pain, and maximal tolerable heat pain was used to define the thresholds.

RESULTS

We found that all three parameters, the detection of warm sensation, heat pain threshold, and heat pain tolerance, were increased during the period when SCS was on compared with when it was off. This increase was observed in both painful and non-painful sites.

CONCLUSION

The observed pain relief during SCS therapy seems to be related to its impact on increased sensory threshold as detected in this study. The increased sensory threshold on areas without pain and without the presence of SCS coverage may indicate a central (spinal and/or supra-spinal) influence from SCS.

Interaction between early life stress and alcohol dependence on neural stress reactivity

Stress response biologic systems are altered in alcohol-dependent individuals. Early life stress (ELS) is associated with a heightened risk of alcohol dependence, presumably because of stress-induced neuroplastic changes. This study was designed to assess the contribution of ELS to a stress-induced neural response in alcohol-dependent participants. Fifteen alcohol-dependent men abstinent for 3-5 weeks and 15 age- and race-matched healthy controls were studied. Anticipatory anxiety was induced by a conditioned stimulus paired with an uncertain physically painful unconditioned stressor. Neural response was assessed with functional magnetic resonance imaging. ELS was assessed with the Childhood Adversity Interview. There was a significant interaction between ELS and group on blood-oxygen-level-dependent (BOLD) amplitude during anticipatory anxiety in the right amygdala and bilateral orbitofrontal cortex, posterior putamen and insula. Higher ELS scores were associated with decreased BOLD amplitude during anticipatory anxiety in alcohol-dependent, but not control, participants. These findings suggest that ELS interacts with alcohol dependence to induce a muted cortico-striatal response to high threat stimuli. Allostatic changes due to both ELS and excessive alcohol use may jointly induce persistent changes in the neural response to acute stressors.

Sensory evoked potentials of the bladder and urethra in middle-aged women: the effect of age

OBJECTIVES

To investigate feasibility, reproducibility and age dependency of sensory evoked cortical potentials (SEPs) after electrical stimulation of different locations in the lower urinary tract (LUT) in a cohort of middle-aged healthy women.

SUBJECTS AND METHODS

In a group of 10 healthy middle-aged women [mean (sd) height 165 (5) cm and age 43 (6) years), electrical stimulation (0.5 and 3 Hz) was applied to the bladder dome, trigone, and proximal and distal urethra. SEPs were recorded at the Cz electrode with reference to Fz. All measurements were repeated three times with an interval of 3-5 weeks. Current perception thresholds (CPT), SEP latencies and amplitudes were analysed. Results were compared with a group of younger women published previously.

RESULTS

LUT SEPs demonstrated two positive (P1, P2) and one negative peak (N1). The mean (sd) N1 latency was 108.9 (7.8), 116.2 (10.7), 113.2 (13.4) and 131.3 (35.6) ms for the bladder dome, trigone, proximal and distal urethra, respectively. N1 latencies, except for the distal urethra, were significantly shorter than those in younger women. Taking all data, i.e. young and middle-aged women, into account, there was a significant negative correlation between the variable age and CPT/dome (r = -0.462, P = 0.04) and N1 latency/dome (r = -0.605, P = 0.005) and a significant positive correlation between the variable age and N1P2 amplitude/dome (r = 0.542, P = 0.014).

CONCLUSION

LUT SEPs can be induced in middle-aged women with reliable N1 responses. Unexpectedly, N1 responses reveal a shortening with increasing age particularly when compared with younger women. Changes in sensory afferents may be explained by age-related qualitative reorganisations within the urothelium and suburothelium potentially altering afferent nerve excitability, which may have an impact on the development of non-neurological LUT symptoms (LUTS, e.g. overactive bladder) in women.

Pain modulation efficiency delays seeking medical help in patients with acute myocardial infarction

Rapid reperfusion is crucial to reduce mortality in patients with ST elevation myocardial infarction. Prehospital patient delay, defined as time from symptoms onset to the decision to seek medical attention, accounts for a large proportion of cases with delayed reperfusion. However, whether pain modulation processes are involved in this phenomenon is not known. We hypothesized that prehospital patient delay may be affected by a reduction of perceived pain perception and pain modulation pattern. Pain threshold, magnitude estimation of suprathreshold stimulation, mechanical temporal summation and conditioned pain modulation (CPM), and recalls of pain magnitude at the onset of chest pain were obtained in 67 patients with first ST elevation myocardial infarction. The study's primary outcome was prehospital patient delay. The median patient delay was 24 (interquartile range, 0.5-72) hours. Of all psychophysical pain measures including pain threshold, magnitude estimation of suprathreshold stimulation, mechanical temporal summation, as well as CPM, only warm sensation threshold was independently associated with lower clinical chest pain intensity (P = 0.01). Multivariable regression analysis (R = 0.449; P < 0.0001) revealed an inverse independent association between chest pain intensity (P < 0.001) and patient delay, whereas efficient CPM was positively associated with prolonged patient delay (P = 0.034). The electrocardiography-derived myocardial ischemic area was not associated with chest pain intensity or patient delay, indicating that the affected ischemic tissue is not a dominant component that determines pain response. In conclusion, beyond the perceived chest pain intensity, the activation pattern of descending inhibition pathways during coronary occlusion affects pain interpretation and behavior during acute coronary occlusion.

Effect of a reversal mirror condition on orofacial mechanical sensitivity

The aim of this study was to investigate whether watching one's own face being touched in a reversal mirror condition modulates orofacial somatosensory sensitivity. A total of 37 healthy volunteers participated in a pilot study, the main study, and a control experiment. In the main experiment, 16 participants received seven different intensities of pinprick stimuli in the right infraorbital region. The perceived stimulus intensity was rated on a 0-50-100 numerical rating scale (NRS). In addition, the pinprick threshold (PiPT) was evaluated in the same region using an electronic von Frey device. During stimuli, participants were watching their own face in two different conditions (normal and reversal mirror) in randomized order. Subjective experiences during each condition were assessed with a questionnaire containing nine statements. The participants rated their level of agreement with the statements using a 7-item Likert scale. There were significant main effects on NRS scores of stimulus forces (p < 0.001) and experimental condition (p < 0.001). Post hoc analyses showed that stimulation with higher force levels induced significantly higher NRS scores (p < 0.001), but interestingly, there were significantly lower NRS scores in the reversal mirror condition than in the normal mirror condition (p < 0.001). There was no significant main effect of experimental condition on PiPT (p = 0.184). The experimental condition influenced the response to several statements significantly (p < 0.001). The somatosensory sensitivity may be impaired when the location of stimulation is not in accordance with the perception. In conclusion, hypoesthetic effects of a reversal mirror were present for fixed force measures but not for threshold measures. Further studies are now needed to describe the potential implications for other somatosensory modalities and orofacial pain conditions.

Does the prevailing hypothesis that small-fiber dysfunction precedes large-fiber dysfunction apply to type 1 diabetic patients?

OBJECTIVE

The prevailing hypothesis that early subclinical small-fiber injury precedes large-fiber damage in diabetic sensorimotor polyneuropathy (DSP) is based on lower intraepithelial nerve fiber density in type 2 prediabetic patients despite normal nerve conduction studies (NCSs). We aimed to confirm the same hypothesis in type 1 diabetic patients by examining whether: (1) subjects without DSP include a spectrum with both normal and abnormal small-fiber measures and (2) subjects with DSP have concurrent evidence of abnormal small-fiber measures.

RESEARCH DESIGN AND METHODS

A healthy control population (n = 53) was used to generate threshold values for four small-fiber tests: cooling detection thresholds (CDTs), laser Doppler imaging of heat-evoked flare (LDIflare), heart rate variability (HRV), and corneal confocal microscopy. Based on NCS results, type 1 diabetic patients (n = 131) were dichotomized according to the presence or absence of DSP.

RESULTS

Threshold values derived from healthy control subjects were 26.5 °C, 1.4 cm2, 13%, and 12.9 mm/mm2 for CDT, LDIflare, HRV, and corneal nerve fiber length, respectively. Among type 1 diabetic patients, 57 of 131 had evidence of DSP, and 74 of 133 did not. Using abnormality of any small-fiber test to define small-fiber dysfunction, 55 of 57 (96.5%) DSP patients and 39 of 74 (52.7%) control subjects without DSP had concurrent small-fiber damage. The severity of small-fiber abnormalities worsened with an increasing number of NCS abnormalities (ANOVA, P < 0.01).

CONCLUSIONS

Our findings in type 1 diabetes support the prevailing hypothesis that small-fiber dysfunction occurs early in DSP. However, further research is required to determine which combination of small-fiber tests is most suitable as a surrogate marker in clinical trials.

Structural and functional small fiber abnormalities in the neuropathic postural tachycardia syndrome

OBJECTIVE

To define the neuropathology, clinical phenotype, autonomic physiology and differentiating features in individuals with neuropathic and non-neuropathic postural tachycardia syndrome (POTS).

METHODS

Twenty-four subjects with POTS and 10 healthy control subjects had skin biopsy analysis of intra-epidermal nerve fiber density (IENFD), quantitative sensory testing (QST) and autonomic testing. Subjects completed quality of life, fatigue and disability questionnaires. Subjects were divided into neuropathic and non-neuropathic POTS, defined by abnormal IENFD and abnormal small fiber and sudomotor function.

RESULTS

Nine of 24 subjects had neuropathic POTS and had significantly lower resting and tilted heart rates; reduced parasympathetic function; and lower phase 4 valsalva maneuver overshoot compared with those with non-neuropathic POTS (P<0.05). Neuropathic POTS subjects also had less anxiety and depression and greater overall self-perceived health-related quality of life scores than non-neuropathic POTS subjects. A sub-group of POTS patients (cholinergic POTS) had abnormal proximal sudomotor function and symptoms that suggest gastrointestinal and genitourinary parasympathetic nervous system dysfunction.

CONCLUSIONS AND RELEVANCE

POTS subtypes may be distinguished using small fiber and autonomic structural and functional criteria. Patients with non-neuropathic POTS have greater anxiety, greater depression and lower health-related quality of life scores compared to those with neuropathic POTS. These findings suggest different pathophysiological processes underlie the postural tachycardia in neuropathic and non-neuropathic POTS patients. The findings have implications for the therapeutic interventions to treat this disorder.

Segmental hyperalgesia to mechanical stimulus in interstitial cystitis/bladder pain syndrome: evidence of central sensitization

PURPOSE

We investigate if subjects with interstitial cystitis/bladder pain syndrome demonstrate mechanical or thermal hyperalgesia, and whether the hyperalgesia is segmental or generalized (global).

MATERIALS AND METHODS

Ten female subjects with interstitial cystitis/bladder pain syndrome and 10 age matched female controls without comorbid fibromyalgia or narcotic use were recruited for quantitative sensory testing. Using the method of limits, pressure pain and heat pain thresholds were measured. Using the method of fixed stimulus, the visual analog scale pain experienced was recorded when a fixed pressure/temperature was applied.

RESULTS

The visual analog scale pain rated by female subjects with interstitial cystitis/bladder pain syndrome was significantly higher than that rated by female control subjects when a fixed mechanical pressure (2 or 4 kg) was applied to the suprapubic (T11) area (p = 0.028). There was an up shift of the stimulus-response curve, which corresponded to the presence of mechanical hyperalgesia in the suprapubic area in interstitial cystitis/bladder pain syndrome. However, the visual analog scale pain rated by subjects with interstitial cystitis/bladder pain syndrome was not different from that rated by controls when a fixed pressure was applied at the other body sites (T1 arm, L4 leg, S2-3 sacral). No difference in visual analog scale pain rating was noted when a fixed heat stimulus (35C or 37C) was applied to any of the body sites tested (T1, T11, L4, S2). There was no difference in pressure pain thresholds or thermal pain thresholds between subjects with interstitial cystitis/bladder pain syndrome and controls.

CONCLUSIONS

Female subjects with interstitial cystitis/bladder pain syndrome showed segmental hyperalgesia to mechanical pressure stimulation in the suprapubic area (T10-T12). This segmental hyperalgesia may be explained in part by spinal central sensitization.

An overview of animal models of pain: disease models and outcome measures

Pain is ultimately a perceptual phenomenon. It is built from information gathered by specialized pain receptors in tissue, modified by spinal and supraspinal mechanisms, and integrated into a discrete sensory experience with an emotional valence in the brain. Because of this, studying intact animals allows the multidimensional nature of pain to be examined. A number of animal models have been developed, reflecting observations that pain phenotypes are mediated by distinct mechanisms. Animal models of pain are designed to mimic distinct clinical diseases to better evaluate underlying mechanisms and potential treatments. Outcome measures are designed to measure multiple parts of the pain experience, including reflexive hyperalgesia measures, sensory and affective dimensions of pain, and impact of pain on function and quality of life. In this review, we discuss the common methods used for inducing each of the pain phenotypes related to clinical pain syndromes as well as the main behavioral tests for assessing pain in each model.

PERSPECTIVE

Understanding animal models and outcome measures in animals will assist in translating data from basic science to the clinic.

Disturbed sensory perception of changes in thermoalgesic stimuli in patients with small fiber neuropathies

The assessment of functional deficits in small fibre neuropathies (SFN) requires using ancillary tests other than conventional neurophysiological techniques. One of the tests with most widespread use is thermal threshold determination, as part of quantitative sensory testing. Thermal thresholds typically reflect one point in the whole subjective experience elicited by a thermal stimulus. We reasoned that more information could be obtained by analyzing the subjective description of the ongoing sensation elicited by slow temperature changes (dynamic thermal testing, DTT). Twenty SFN patients and 20 healthy subjects were requested to describe, by using an electronic visual analog scale system, the sensation perceived when the temperature of a thermode was made to slowly change according to a predetermined pattern. The thermode was attached to the left ventral forearm or the distal third of the left leg and the stimulus was either a monophasic heat or cold stimuli that reached 120% of pain threshold and reversed to get back to baseline at a rate of 0.5 °C/s. Abnormalities seen in patients in comparison to healthy subjects were: (1) delayed perception of temperature changes, both at onset and at reversal, (2) longer duration of pain perception at peak temperature, and (3) absence of an overshoot sensation after reversal, ie, a transient perception of the opposite sensation before the temperature reached again baseline. The use of DTT increases the yield of thermal testing for clinical and physiological studies. It adds information that can be discriminant between healthy subjects and SFN patients and shows physiological details about the process of activation and inactivation of temperature receptors that may be abnormal in SFN.

Pattern-recognition approach to neuropathy and neuronopathy

Neuropathic disorders encompass those that affect the neuron's cell body or neuronopathies, those affecting the peripheral process, or peripheral neuropathies. The peripheral neuropathies can be broadly subdivided into the myelinopathies and axonopathies, conditions which can be hereditary or acquired. Each of these disorders has distinct clinical features that enable neurologists to recognize the various patterns of presentation. Once a particular pattern is established, further laboratory studies can be performed to support the clinical impression.

A human model of small fiber neuropathy to study wound healing

The aim of this study was to develop a human model of acute wound healing that isolated the effects of small fiber neuropathy on the healing process. Twenty-five healthy subjects had the transient receptor vanilloid 1 agonist capsaicin and placebo creams topically applied to contralateral areas on the skin of the thigh for 48 hours. Subjects had shallow (1.2 millimeter) and deep (>3 millimeter) punch skin biopsies from each thigh on days 1 and 14. Biopsy wound healing was monitored photographically until closure. Intra-epidermal and sweat-gland nerve fiber densities were measured for each biopsy. Shallow wounds in capsaicin-treated sites healed more slowly than in placebo treated skin with biopsies taken on day 1 (P<0.001) and day 14 (P<0.001). Deep biopsies in the capsaicin and placebo areas healed at similar rates at both time points. Nerve fiber densities were reduced only in capsaicin treated regions (P<0.01). In conclusion, topical application of capsaicin causes a small fiber neuropathy and is associated with a delay in healing of shallow, but not deep wounds. This novel human model may prove valuable in the study of wound healing in patients with neuropathy.

Experimental pain and opioid analgesia in volunteers at high risk for obstructive sleep apnea

Background

Obstructive sleep apnea (OSA) is characterized by recurrent nocturnal hypoxia and sleep disruption. Sleep fragmentation caused hyperalgesia in volunteers, while nocturnal hypoxemia enhanced morphine analgesic potency in children with OSA. This evidence directly relates to surgical OSA patients who are at risk for airway compromise due to postoperative use of opioids. Using accepted experimental pain models, we characterized pain processing and opioid analgesia in male volunteers recruited based on their risk for OSA.

Methods

After approval from the Intitutional Review Board and informed consent, we assessed heat and cold pain thresholds and tolerances in volunteers after overnight polysomnography (PSG). Three pro-inflammatory and 3 hypoxia markers were determined in the serum. Pain tests were performed at baseline, placebo, and two effect site concentrations of remifentanil (1 and 2 µg/ml), an μ-opioid agonist. Linear mixed effects regression models were employed to evaluate the association of 3 PSG descriptors [wake after sleep onset, number of sleep stage shifts, and lowest oxyhemoglobin saturation (SaO₂) during sleep] and all serum markers with pain thresholds and tolerances at baseline, as well as their changes under remifentanil.

Results

Forty-three volunteers (12 normal and 31 with a PSG-based diagnosis of OSA) were included in the analysis. The lower nadir SaO₂ and higher insulin growth factor binding protein-1 (IGFBP-1) were associated with higher analgesic sensitivity to remifentanil (SaO₂, P = 0.0440; IGFBP-1, P = 0.0013). Other pro-inflammatory mediators like interleukin-1β and tumor necrosis factor-α (TNF-α) were associated with an enhanced sensitivity to the opioid analgesic effect (IL-1β, P = 0.0218; TNF-α, P = 0.0276).

Conclusions

Nocturnal hypoxemia in subjects at high risk for OSA was associated with an increased potency of opioid analgesia. A serum hypoxia marker (IGFBP-1) was associated with hypoalgesia and increased potency to opioid analgesia; other pro-inflammatory mediators also predicted an enhanced opioid potency.

Trial Registration: ClinicalTrials.gov

NCT00672737.

Quantitative thermal sensory testing and sympathetic skin response in primary Restless legs syndrome - A prospective study on 57 Indian patients

Patients with restless leg syndrome present with sensory symptoms similar to peripheral neuropathy. While there is evidence of abnormalities of dopaminergic pathways, the peripheral nervous system has been studied infrequently. We studied conventional nerve conduction studies, quantitative thermal sensory testing and sympathetic skin response in 57 patients with primary restless leg syndrome. Almost two third patients demonstrated abnormalities in the detailed testing of the peripheral nervous system. Sbtle abnormalities of the peripheral nervous system may be more common than previously believed.

The effect of post-surgical neuroplasticity on the stability of systemic pain perception: a psychophysical study

BACKGROUND

Surgery-induced neuroplasticity at spinal and supra-spinal levels is assumed to evoke a clinical acute post-operative pain (cAPOP) experience, which is expressed by allodynia and/or hyperalgesia. It remains unclear whether the systemic pain perception measured outside the incision area remains unchanged and whether it is affected by the presence of cAPOP.

AIMS

This study explored whether the systemic perception of experimental pain would be altered towards hypersensitivity following elective gynecological surgery unmasked by opioids.

METHODS

A perioperative psychophysical evaluation of heat pain thresholds (HPT) and pain estimations were obtained in a remote bodily area before and after surgery among 35 women.

RESULTS

The ratings for both pain dimensions of intensity and unpleasantness remained stable following surgery. However, there was a reduction found in HPT the day after surgery (43.6 ± 2.2 °C to 42.2 ± 3.1 °C, p = 0.002). This reduction was associated with lower HPT measured before surgery (r = .56, p < 0.000) and with higher cAPOP intensity obtained at rest (r = -.44, p = 0.008).

CONCLUSIONS

This post-surgical allodynia, as reflected by the systemic enhancement of pain perception, may represent plasticity in the central pain pathways at the supra-spinal level. Pre-surgical assessment of a patient's pain perception profile may predict certain pain dimensions of post-surgical pain plasticity. The evaluation of individual pain profiles may contribute to a mechanism-based approach aimed to attenuate the cAPOP.

Striatal-limbic activation is associated with intensity of anticipatory anxiety

Anxiety experienced in anticipation of impending aversive events induces striatal-limbic activation. However, previous functional magnetic imaging (fMRI) studies of anticipatory anxiety have utilized post-test measures of anxiety, making a direct association between neural activation and distress problematic. This paradigm was designed to assess the blood-oxygen-level-dependent (BOLD) response to an aversive conditioned stimulus while simultaneously measuring subjective anxiety. Fifteen male healthy subjects (45.5±8.5 years old) were studied. A high-threat conditioned stimulus (CS) was paired with either an unpredictable, highly aversive (painful) or non-aversive (non-painful) unconditioned stimulus and compared to a low-threat CS paired with a predictable, non-aversive stimulus. Neural response was assessed with fMRI, and subjective anxiety (1-4) was recorded upon the presentation of each CS. High subjective ratings of real-time anticipatory anxiety (2-4), relative to low anticipatory anxiety (1), elicited increased activation in the bilateral striatum, bilateral orbital frontal cortex, left anterior insula, and anterior cingulate cortex (ACC) and decreased activation in the posterior cingulate cortex (PCC). The amplitude of BOLD signal change generally paralleled the subjective rating of anxiety. Real-time measures of anticipatory anxiety confirm previous reports, using post-test measures of anxiety, of striatal-limbic activation during anticipatory anxiety while simultaneously demonstrating an increase in BOLD response in parallel with heightened anxiety.

Quantitative sensory testing of neuropathic pain patients: potential mechanistic and therapeutic implications

Quantitative sensory testing (QST) is a widely accepted tool to investigate somatosensory changes in pain patients. Many different protocols have been developed in clinical pain research within recent years. In this review, we provide an overview of QST and tested neuroanatomical pathways, including peripheral and central structures. Based on research studies using animal and human surrogate models of neuropathic pain, possible underlying mechanisms of chronic pain are discussed. Clinically, QST may be useful for 1) the identification of subgroups of patients with different underlying pain mechanisms; 2) prediction of therapeutic outcomes; and 3) quantification of therapeutic interventions in pain therapy. Combined with sensory mapping, QST may provide useful information on the site of neural damage and on mechanisms of positive and negative somatosensory abnormalities. The use of QST in individual patients for diagnostic purposes leading to individualized therapy is an interesting concept, but needs further validation.

Reliability of the method of levels for determining cutaneous temperature sensitivity

Determination of the thermal thresholds is used clinically for evaluation of peripheral nervous system function. The aim of this study was to evaluate reliability of the method of levels performed with a new, low cost device for determining cutaneous temperature sensitivity. Nineteen male subjects were included in the study. Thermal thresholds were tested on the right side at the volar surface of mid-forearm, lateral surface of mid-upper arm and front area of mid-thigh. Thermal testing was carried out by the method of levels with an initial temperature step of 2°C. Variability of thermal thresholds was expressed by means of the ratio between the second and the first testing, coefficient of variation (CV), coefficient of repeatability (CR), intraclass correlation coefficient (ICC), mean difference between sessions (S1-S2diff), standard error of measurement (SEM) and minimally detectable change (MDC). There were no statistically significant changes between sessions for warm or cold thresholds, or between warm and cold thresholds. Within-subject CVs were acceptable. The CR estimates for warm thresholds ranged from 0.74°C to 1.06°C and from 0.67°C to 1.07°C for cold thresholds. The ICC values for intra-rater reliability ranged from 0.41 to 0.72 for warm thresholds and from 0.67 to 0.84 for cold thresholds. S1-S2diff ranged from -0.15°C to 0.07°C for warm thresholds, and from -0.08°C to 0.07°C for cold thresholds. SEM ranged from 0.26°C to 0.38°C for warm thresholds, and from 0.23°C to 0.38°C for cold thresholds. Estimated MDC values were between 0.60°C and 0.88°C for warm thresholds, and 0.53°C and 0.88°C for cold thresholds. The method of levels for determining cutaneous temperature sensitivity has acceptable reliability.

New insights into the clinical evaluation of hereditary transthyretin amyloidosis patients: a single center's experience

Over the last decade, new medical treatment modalities have emerged based on increased insights into amyloid formation. With the increased possibilities for treatment of amyloidosis caused by transthyretin (TTR) amyloid deposits comes the need for diagnostic procedures for early diagnosis and better tools to follow disease progression. This is of particular importance in clinical trials evaluating the efficacy of new treatments. Until recently, the treatment of TTR amyloidosis (ATTR) was based solely on liver transplantation, a procedure that has halted disease progression in many patients. Liver transplantation has been especially effective in patients under the age of 50 years carrying the TTR V30M mutation, whereas the outcome of the procedure has been variable for others, particularly elderly male patients and those carrying a non-V30M mutation. This review concentrates on new insights derived from our center's experience with liver transplantation, how to implement this experience in evaluation of new treatment modalities for ATTR, and how to facilitate early diagnosis of neuropathy with easily available diagnostic tools. Attention has focused on manifestations of the disease that involve the heart and the peripheral nervous system; change in peripheral nerve function has been the primary endpoint in two controlled clinical trials, one finished and one ongoing. New insights into the amyloid formation process and the lessons learned from liver transplantation give the opportunity to design potentially effective treatment modalities for ATTR. It appears reasonable to suspect that a combination of different treatment modalities may be required to treat the disease, and that different treatment regimes will be designed according to the phenotype of the disease. For the patients and their relatives there is now a solid foundation for optimism, with prospects of several effective medical treatment possibilities within the coming decade.

Sensibility of the ear after otoplasty

Changes in skin sensibility occur in various postoperative plastic surgeries, especially when they involve major skin and subcutaneous dissection. There were no studies so far that objectively compared changes of ear sensibility. This prospective study was conducted to compare ear sensibility before and after otoplasty. Patients with prominent ears (n = 15) underwent bilateral otoplasty. Ear tactile sensibility was tested preoperatively and 6 and 12 months after surgery by Pressure Specified Sensory Device, an apparatus that quantifies cutaneous pressure sensation (g/mm(2)). Comparison between preoperative and 6-months postoperative results indicated an increment on mean skin pressure thresholds; however, mean thresholds between pre- and 12 months postoperative period were similar. Vibratory and hot/cold sensibility did not present any difference during this period. This is the first comparative assessment of ear tactile sensibility using quantitative methods. After otoplasty, initially there was reduction in an ear tactile sensibility, followed by a return to levels similar to preoperative sensibility.

Evaluation of proxy tests for SFSN: evidence for mixed small and large fiber dysfunction

Background

Though intra-epidermal nerve fiber density (IENFD) is considered the gold standard for diagnosis of small fiber sensory neuropathy (SFSN), we aimed to determine if novel threshold values derived from standard tests of small or large fiber function could serve as diagnostic alternatives.

Methods

Seventy-four consecutive patients with painful polyneuropathy and normal nerve conduction studies (NCS) were defined as SFSN cases or controls by distal IENFD <5.4 and ≥5.4 fibers/mm, respectively. Diagnostic performance of small fiber [cooling (CDT) and heat perception (HP) thresholds, axon reflex-mediated neurogenic vasodilatation] and large fiber function tests [vibration perception thresholds (VPT) and sural nerve conduction parameters] were determined by receiver operating-characteristic (ROC) curve analyses.

Results

The 26(35%) SFSN cases had mean IENFD 3.3±1.7 fibers/mm and the 48(65%) controls 9.9±2.9 fibers/mm. Male gender (p = 0.02) and older age (p = 0.02) were associated with SFSN cases compared to controls. VPT were higher and CDT lower in SFSN cases, but the largest magnitude of differences was observed for sural nerve amplitude. It had the greatest area under the ROC curve (0.75) compared to all other tests (p<0.001 for all comparisons) and the optimal threshold value of ≤12 µV defined SFSN cases with 80% sensitivity and 72% specificity.

Conclusion

In patients presenting with polyneuropathy manifestations and normal NCS, though small fiber function tests were intuitively considered the best alternative measures to predict reduced IENFD, their diagnostic performance was poor. Instead, novel threshold values within the normal range for large fiber tests should be considered as an alternative strategy to select subjects for skin biopsy in diagnostic protocols for SFSN.

Sensory nerve action potentials and sensory perception in women with arthritis of the hand

Background

Arthritis of the hand can limit a person’s ability to perform daily activities. Whether or not sensory deficits contribute to the disability in this population remains unknown. The primary purpose of this study was to determine if women with osteoarthritis (OA) or rheumatoid arthritis (RA) of the hand have sensory impairments.

Methods

Sensory function in the dominant hand of women with hand OA or RA and healthy women was evaluated by measuring sensory nerve action potentials (SNAPs) from the median, ulnar and radial nerves, sensory mapping (SM), and vibratory and current perception thresholds (VPT and CPT, respectively) of the second and fifth digits.

Results

All SNAP amplitudes were significantly lower for the hand OA and hand RA groups compared with the healthy group (p < 0.05). No group differences were found for SNAP conduction velocities, SM, VPT, and CPT.

Discussion

We propose, based on these findings, that women with hand OA or RA may have axonal loss of sensory fibers in the median, ulnar and radial nerves. Less apparent were losses in conduction speed or sensory perception.

Diabetic neuropathy and axon reflex-mediated neurogenic vasodilatation in type 1 diabetes

Objective

Axon reflex-mediated neurogenic vasodilatation in response to cutaneous heating may reflect early, pre-clinical small fibre dysfunction. We aimed to evaluate the distribution of the vascular flare area measured by laser doppler imaging (“LDI_FLARE area”) in type 1 diabetes and in healthy volunteers.

Research and Methods

Concurrent with clinical and electrophysiological examination to classify diabetic sensorimotor polyneuropathy (DSP), LDI_FLARE area (cm²) was determined in 89 type 1 diabetes subjects matched to 64 healthy volunteers. We examined the association and diagnostic performance of LDI with clinical and subclinical measures of DSP and its severity.

Results

Compared to the 64 healthy volunteers, the 56 diabetes controls without DSP had significantly lower LDI_FLARE area (p = 0.006). The 33 diabetes cases with DSP had substantially lower LDI_FLARE area as compared to controls without DSP (p = 0.002). There was considerable overlap in LDI_FLARE area between all groups such that the ROC curve had an AUC of 0.72 and optimal sensitivity of 70% for the detection of clinical DSP. Use of a subclinical definition for DSP, according to subclinical sural nerve impairment, was associated with improved AUC of 0.75 and sensitivity of 79%. In multivariate analysis higher HbA1c and body mass index had independent associations with smaller LDI_FLARE area.

Conclusions

Axon reflex-mediated neurogenic vasodilatation in response to cutaneous heating is a biomarker of early nerve dysfunction in DSP. Its independent association with glycemic exposure in diabetes subjects and both glycemic exposure and BMI in healthy volunteers highlights the existence of small-fibre dysfunction in the natural history of DSP.

Conditioned pain modulation predicts duloxetine efficacy in painful diabetic neuropathy

This study aims to individualize the selection of drugs for neuropathic pain by examining the potential coupling of a given drug's mechanism of action with the patient's pain modulation pattern. The latter is assessed by the conditioned pain modulation (CPM) and temporal summation (TS) protocols. We hypothesized that patients with a malfunctioning pain modulation pattern, such as less efficient CPM, would benefit more from drugs augmenting descending inhibitory pain control than would patients with a normal modulation pattern of efficient CPM. Thirty patients with painful diabetic neuropathy received 1 week of placebo, 1 week of 30 mg/d duloxetine, and 4 weeks of 60 mg/d duloxetine. Pain modulation was assessed psychophysically, both before and at the end of treatment. Patient assessment of drug efficacy, assessed weekly, was the study's primary outcome. Baseline CPM was found to be correlated with duloxetine efficacy (r=0.628, P<.001, efficient CPM is marked negative), such that less efficient CPM predicted efficacious use of duloxetine. Regression analysis (R(2)=0.673; P=.012) showed that drug efficacy was predicted only by CPM (P=.001) and not by pretreatment pain levels, neuropathy severity, depression level, or patient assessment of improvement by placebo. Furthermore, beyond its predictive value, the treatment-induced improvement in CPM was correlated with drug efficacy (r=-0.411, P=.033). However, this improvement occurred only in patients with less efficient CPM (16.8±16.0 to -1.1±15.5, P<.050). No predictive role was found for TS. In conclusion, the coupling of CPM and duloxetine efficacy highlights the importance of pain pathophysiology in the clinical decision-making process. This evaluative approach promotes personalized pain therapy.

FMRI reveals abnormal central processing of sensory and pain stimuli in ill Gulf War veterans

Many veterans chronically ill from the 1991 Gulf War exhibit symptoms of altered sensation, including chronic pain. In this study of 55 veterans of a Construction Battalion previously examined in 1995-1996 and 1997-1998, brain activation to innocuous and noxious heat stimuli was assessed in 2008-2009 with a quantitative sensory testing fMRI protocol in control veterans and groups representing three syndrome variants. Testing outside the scanner revealed no significant differences in warm detection or heat pain threshold among the four groups. In the fMRI study, Syndrome 1 and Syndrome 2, but not Syndrome 3, exhibited hypo-activation to innocuous heat and hyper-activation to noxious heat stimuli compared to controls. The results indicate abnormal central processing of sensory and painful stimuli in 2 of 3 variants of Gulf War illness and call for a more comprehensive study with a larger, representative sample of veterans.

Mechanisms of neuropathic pain

Neuropathic pain is a disease of global burden. Its symptoms include spontaneous and stimulus-evoked painful sensations. Several maladaptive mechanisms underlying these symptoms have been elucidated in recent years: peripheral sensitization of nociception, abnormal excitability of afferent neurons, central sensitization comprising pronociceptive facilitation, disinhibition of nociception and central reorganization processes, and sympathetically maintained pain. This review aims to illustrate these pathophysiological principles, focussing on molecular and neurophysiological findings. Finally therapeutic options based on these findings are discussed.

The effect of venlafaxine on ongoing and experimentally induced pain in neuropathic pain patients: a double blind, placebo controlled study

BACKGROUND AND AIM

The aim of this randomized double blind placebo controlled study was to investigate the effectiveness and the safety of venlafaxine XR 75 and 150 mg on ongoing pain and on quantitative sensory tests in 60 patients with neuropathic pain for 8 weeks.

METHODS

Evaluation parameters consisted of ongoing pain intensity (VAS), patient satisfaction, side effects, global efficacy and tolerance. Quantitative sensory measurements taken from the affected area before and after the drug treatment included pin-prick hyperalgesia, allodynia, detection and pain thresholds to electrical and heat stimuli, temporal summation of repetitive electrical and heat stimuli.

RESULTS

A total of 55 patients completed the study. VAS scores decreased significantly compared to the baseline measurements in all groups. There was no significant difference between the groups regarding pain intensity and escape medication. The areas of allodynia and pin-prick hyperalgesia decreased significantly in venlafaxine groups compared to the placebo. There was no significant difference between the groups regarding the detection thresholds (electrical and heat). The pain threshold and the summation threshold to electrical stimuli and the summation threshold to heat stimuli increased significantly following treatment in both venlafaxine groups. In addition, the degree of the temporal summation to electrical and heat stimuli decreased significantly following treatment in both venlafaxine groups compared to the placebo.

CONCLUSION

The study showed significant effect of venlafaxine in the manifestations of hyperalgesia and temporal summation, but not on the ongoing pain intensity. Furthermore, the quantitative sensory tests provided complementing information to the clinical measures.

Characteristics of response to experimental pain in sexually abused women

OBJECTIVES

Women with a history of sexual abuse (SA) commonly report greater pain symptoms. It is still unclear whether enhanced pain susceptibility is the result of altered pain processing and response. Therefore, this pilot study aimed to explore pain sensitivity to experimentally induced pain and associated psychology in women with a history of severe SA.

METHODS

Twenty-one survivors of severe, long-lasting SA and 21 control women underwent experimentally induced heat pain and completed psychological questionnaires. Pain measures included heat pain thresholds, pain intensity ratings, and pain tolerance in response to contact heat, painful stimulation delivered to the volar forearm. Questionnaires included somatization (Brief Symptom Inventory), personality traits including harm avoidance, novelty seeking, and reward dependence (Cloninger tridimensional personality questionnaire), and levels of dissociation (Dissociative Experiences Scale).

RESULTS

SA women had elevated heat pain thresholds (45.7±2.2°C vs. 43.9±3.1°C; P=0.042) and higher pain intensity ratings (on a 0 to 100 scale: 80.0±26.6 vs. 51.2±27.7; P=0.001). In addition, they had lower tolerability to painful tonic stimulation, greater somatization, and larger harm avoidance scores. Regression analyses showed that higher pain intensity ratings in SA women associated with greater tendency for harm avoidance but not with levels of dissociation.

DISCUSSION

Women with a history of severe SA seem to have a paradoxical pattern of experimental pain response, characterized by both higher pain thresholds and increased pain intensity ratings. This pattern is associated with the personality trait of harm avoidance. Models that might account for these findings are discussed.

Reproducibility of in vivo corneal confocal microscopy as a novel screening test for early diabetic sensorimotor polyneuropathy

AIM

With the goal of identifying a valid biomarker of early diabetic sensorimotor polyneuropathy, we aimed to identify the most reliable in vivo corneal confocal microscopy (CCM) parameter for detection of abnormality of small nerve fibre morphology.

METHODS

Cross-sectional examination of 46 subjects (26 with Type 1 diabetes and 20 healthy volunteers) examined by corneal confocal microscopy for intra- and interobserver reproducibility by the intraclass correlation coefficient method. Corneal nerve fibre density, nerve branch density, nerve fibre length and tortuosity were measured on the same day that subjects underwent clinical and electrophysiological examination.

RESULTS

The 26 subjects with Type 1 diabetes had mean age and diabetes duration 42.8 ± 16.9 and 22.7 ± 16.4 years, respectively. Twelve of those subjects (46%) did not meet criteria for diabetic sensorimotor polyneuropathy, while five (19%) had mild, three (12%) had moderate and six (23%) had severe diabetic sensorimotor polyneuropathy. None of the healthy volunteers (mean age 41.4 ± 17.3 years) had polyneuropathy. Re-examination of selected corneal confocal microscopy images or sets of 40 images yielded very good to excellent intraclass correlation coefficients for all parameters. However, only one parameter (corneal nerve fibre length) emerged with consistently very good reproducibility using a clinically relevant 'study-level' protocol of subject re-examination (intra-observer intraclass correlation coefficient 0.72; interobserver intraclass correlation coefficient 0.73). Despite no differences in intraclass correlation coefficient between subgroups, corneal nerve fibre length was significantly lower (14.76 vs. 16.15 mm/mm(2), P = 0.04) in those with diabetes.

CONCLUSIONS

Development of corneal confocal microscopy may need to focus on the measurement of corneal nerve fibre length, as it appears to have superior reliability in comparison with other parameters, and as evidence exists for its potential as a clinical biomarker of early diabetic sensorimotor polyneuropathy.

A clínica da psicofísica

Apresentamos a Psicofísica como uma ciência aplicada nas investigações e nas abordagens e diagnósticos clínicos. Inicialmente, introduzimos algo dos aspectos epistemológicos e teóricos da área, passamos para as abordagens que a Psicofísica pode apresentar na aplicabilidade clínica e, por fim, discutimos os avanços recentes da aplicação clínica, apresentamos as experiências de nosso laboratório de pesquisa clínica em psicofísica, finalizando com as perspectivas de ampliação do uso da psicofísica para investigações clínicas de funções perceptuais mais complexas.

Capsaicin induces degeneration of cutaneous autonomic nerve fibers

OBJECTIVE

To determine the effects of topical application of capsaicin on cutaneous autonomic nerves.

METHODS

Thirty-two healthy subjects underwent occlusive application of 0.1% capsaicin cream (or placebo) for 48 hours. Subjects were followed for 6 months with serial assessments of sudomotor, vasomotor, pilomotor, and sensory function with simultaneous assessment of innervation through skin biopsies.

RESULTS

There were reductions in sudomotor, vasomotor, pilomotor, and sensory function in capsaicin-treated subjects (p < 0.01 vs. placebo). Sensory function declined more rapidly than autonomic function, reaching a nadir by Day 6, whereas autonomic function reached a nadir by Day 16. There were reductions in sudomotor, vasomotor, pilomotor, and sensory nerve fiber densities in capsaicin-treated subjects (p < 0.01 vs. placebo). Intraepidermal nerve fiber density declined maximally by 6 days, whereas autonomic nerve fiber densities reached maximal degeneration by Day 16. Conversely, autonomic nerves generally regenerated more rapidly than sensory nerves, requiring 40-50 days to return to baseline levels, whereas sensory fibers required 140-150 days to return to baseline.

INTERPRETATION

Topical capsaicin leads to degeneration of sudomotor, vasomotor, and pilomotor nerves accompanied by impairment of sudomotor, vasomotor, and pilomotor function. These results suggest the susceptibility and/or pathophysiologic mechanisms of nerve damage may differ between autonomic and sensory nerve fibers treated with capsaicin and enhances the capsaicin model for the study of disease-modifying agents. The data suggest caution should be taken when topical capsaicin is applied to skin surfaces at risk for ulceration, particularly in neuropathic conditions characterized by sensory and autonomic impairment.

Guidelines and recommendations for assessment of somatosensory function in oro-facial pain conditions--a taskforce report

The goals of an international taskforce on somatosensory testing established by the Special Interest Group of Oro-facial Pain (SIG-OFP) under the International Association for the Study of Pain (IASP) were to (i) review the literature concerning assessment of somatosensory function in the oro-facial region in terms of techniques and test performance, (ii) provide guidelines for comprehensive and screening examination procedures, and (iii) give recommendations for future development of somatosensory testing specifically in the oro-facial region. Numerous qualitative and quantitative psychophysical techniques have been proposed and used in the description of oro-facial somatosensory function. The selection of technique includes time considerations because the most reliable and accurate methods require multiple repetitions of stimuli. Multiple-stimulus modalities (mechanical, thermal, electrical, chemical) have been applied to study oro-facial somatosensory function. A battery of different test stimuli is needed to obtain comprehensive information about the functional integrity of the various types of afferent nerve fibres. Based on the available literature, the German Neuropathic Pain Network test battery appears suitable for the study of somatosensory function within the oro-facial area as it is based on a wide variety of both qualitative and quantitative assessments of all cutaneous somatosensory modalities. Furthermore, these protocols have been thoroughly described and tested on multiple sites including the facial skin and intra-oral mucosa. Standardisation of both comprehensive and screening examination techniques is likely to improve the diagnostic accuracy and facilitate the understanding of neural mechanisms and somatosensory changes in different oro-facial pain conditions and may help to guide management.

Test-retest and interobserver reliability of quantitative sensory testing according to the protocol of the German Research Network on Neuropathic Pain (DFNS): a multi-centre study

Quantitative sensory testing (QST) is an instrument to assess positive and negative sensory signs, helping to identify mechanisms underlying pathologic pain conditions. In this study, we evaluated the test-retest reliability (TR-R) and the interobserver reliability (IO-R) of QST in patients with sensory disturbances of different etiologies. In 4 centres, 60 patients (37 male and 23 female, 56.4±1.9years) with lesions or diseases of the somatosensory system were included. QST comprised 13 parameters including detection and pain thresholds for thermal and mechanical stimuli. QST was performed in the clinically most affected test area and a less or unaffected control area in a morning and an afternoon session on 2 consecutive days by examiner pairs (4 QSTs/patient). For both, TR-R and IO-R, there were high correlations (r=0.80-0.93) at the affected test area, except for wind-up ratio (TR-R: r=0.67; IO-R: r=0.56) and paradoxical heat sensations (TR-R: r=0.35; IO-R: r=0.44). Mean IO-R (r=0.83, 31% unexplained variance) was slightly lower than TR-R (r=0.86, 26% unexplained variance, P<.05); the difference in variance amounted to 5%. There were no differences between study centres. In a subgroup with an unaffected control area (n=43), reliabilities were significantly better in the test area (TR-R: r=0.86; IO-R: r=0.83) than in the control area (TR-R: r=0.79; IO-R: r=0.71, each P<.01), suggesting that disease-related systematic variance enhances reliability of QST. We conclude that standardized QST performed by trained examiners is a valuable diagnostic instrument with good test-retest and interobserver reliability within 2days. With standardized training, observer bias is much lower than random variance. Quantitative sensory testing performed by trained examiners is a valuable diagnostic instrument with good interobserver and test-retest reliability for use in patients with sensory disturbances of different etiologies to help identify mechanisms of neuropathic and non-neuropathic pain.

Thermal sensitivity in the elderly: a review

Aging is associated with a progressive decrease in thermal perception, as revealed by increased thermal detection thresholds in the elderly. This reduction in thermosensitivity follows a distal-proximal pattern, with more pronounced decrements observed in the limbs and in the perception of warmth vs. cold. The main underlying causes of this seem to be aging of the skin and subsequent reductions in thermoreceptor density and superficial skin blood flow. However, the results from some animal studies also suggest that changes in the peripheral nerve system, particularly fiber loss and decreased conduction velocity, may also be involved. In this paper, we review age-related changes in the thermal sensitivity of humans, their underlying mechanisms, and the strengths and limitations of some of the methodologies used to assess these changes.

Thermal hypesthesia in patients with complex regional pain syndrome related dystonia

The quantitative thermal test showed cold and warmth hypesthesia without increased heat pain sensitivity in the affected limbs of complex regional pain syndrome (CRPS) patients with tonic dystonia (n = 44) in comparison with healthy controls with a similar age and sex distribution (n = 35). The degrees of cold and warmth hypesthesia were strongly correlated. We conclude that dysfunction in small nerve fiber (i.e., C and Aδ) processing is present in patients with CRPS-related dystonia.

Diabetic neuropathy: a cross-sectional study of the relationships among tests of neurophysiology

OBJECTIVE

To determine the relationships among large, small, and autonomic fiber neurophysiological measures in a cross-sectional study of patients with diabetes.

RESEARCH DESIGN AND METHODS

We assessed 130 individuals: 25 healthy subjects and 105 subjects with diabetes. Subjects were classified by the presence or absence of neuropathy by physical examination. All subjects underwent autonomic testing, nerve conduction studies, quantitative sensory testing, and nerve-axon reflex vasodilation in addition to quantifiable neurological examination and symptom scores. Correlation and cluster analysis were used to determine relationships between and among different neurophysiological testing parameters.

RESULTS

Results of neurophysiological tests were abnormal in patients with clinical evidence of diabetic neuropathy compared with results in healthy control subjects and in those without neuropathy (P < 0.01, all tests). The correlations among individual tests varied widely, both within (r range <0.5->0.9, NS to <0.001) and between test groups (r range <0.2->0.5, NS to <0.01). A two-step hierarchical cluster analysis revealed that neurophysiological tests do not aggregate by typical "small," "large," or "autonomic" nerve fiber subtypes.

CONCLUSIONS

The modest correlation coefficients seen between the different testing modalities suggest that these techniques measure different neurophysiological parameters and are therefore not interchangeable. However, the data suggest that only a small number of neurophysiological tests are actually required to clinically differentiate individuals with neuropathy from those without. The natural clustering of both patients and healthy control subjects suggests that variations in the population will need to be considered in future studies of diabetic neuropathy.