The nociceptive withdrawal reflex: Normative values of thresholds and reflex receptive fields

Assessments of spinal nociceptive withdrawal reflexes can be used in human research both to evaluate the effect of analgesics and explore pain mechanisms related to sensitization. Before the reflex can be used as a clinical tool, normative values need to be determined in large scale studies. The aim of this study was to determine the reference values of spinal nociceptive reflexes and subjective pain thresholds (to single and repeated stimulation), and of the area of the reflex receptive fields (RRF) in 300 pain‐free volunteers. The influences of gender, age, height, weight, body‐mass index (BMI), body side of testing, depression, anxiety, catastrophizing and parameters of Short‐Form 36 (SF‐36) were analyzed by multiple regressions. The 95% confidence intervals were determined for all the tests as normative values. Age had a statistically and quantitatively significant impact on the subjective pain threshold to single stimuli. The reflex threshold to single stimulus was lower on the dominant compared to the non‐dominant side. Depression had a negative impact on the subjective pain threshold to single stimuli. All the other analyses either did not reveal statistical significance or displayed quantitatively insignificant correlations. In conclusion, normative values of parameters related to the spinal nociceptive reflex were determined. This allows their clinical application for assessing central hyperexcitability in individual patients. The parameters investigated explore different aspects of sensitization processes that are largely independent of demographic characteristics, cognitive and affective factors.     

Quantitative sensory testing in the German Research Network on Neuropathic Pain (DFNS): standardized protocol and reference values

The nationwide multicenter trials of the German Research Network on Neuropathic Pain (DFNS) aim to characterize the somatosensory phenotype of patients with neuropathic pain. For this purpose, we have implemented a standardized quantitative sensory testing (QST) protocol giving a complete profile for one region within 30 min. To judge plus or minus signs in patients we have now established age- and gender-matched absolute and relative QST reference values from 180 healthy subjects, assessed bilaterally over face, hand and foot. We determined thermal detection and pain thresholds including a test for paradoxical heat sensations, mechanical detection thresholds to von Frey filaments and a 64 Hz tuning fork, mechanical pain thresholds to pinprick stimuli and blunt pressure, stimulus/response-functions for pinprick and dynamic mechanical allodynia, and pain summation (wind-up ratio). QST parameters were region specific and age dependent. Pain thresholds were significantly lower in women than men. Detection thresholds were generally independent of gender. Reference data were normalized to the specific group means and variances (region, age, gender) by calculating z-scores. Due to confidence limits close to the respective limits of the possible data range, heat hypoalgesia, cold hypoalgesia, and mechanical hyperesthesia can hardly be diagnosed. Nevertheless, these parameters can be used for group comparisons. Sensitivity is enhanced by side-to-side comparisons by a factor ranging from 1.1 to 2.5. Relative comparisons across body regions do not offer advantages over absolute reference values. Application of this standardized QST protocol in patients and human surrogate models will allow to infer underlying mechanisms from somatosensory phenotypes.     

Habituation and sensitization to heat and cold pain in women with fibromyalgia and healthy controls

The purpose of this study was to examine differences in habituation to heat and cold pain in women with fibromyalgia (FM; n = 33) and in women who were healthy controls (HC; n = 44). Quantitative sensory testing (QST) was used to assess pain thresholds during five consecutive trials of ascending heat and descending cold stimulation. Anxiety, depression, fatigue, and pain during the previous week were assessed using self-report measures. The overall hypotheses were that there would be differences between groups in pain thresholds and in the rate of habituation to heat and cold pain stimuli. Multilevel modeling was used to test the hypotheses. There were large overall differences in pain thresholds, with the FM group showing greater sensitivity to heat and cold pain stimuli compared with the HC group. While habituation occurred in both of the groups for heat pain, the HC group had stronger habituation across trials than the FM group. Conversely, while the HC group habituated to cold pain stimuli, the FM group showed sensitization and had decreased cold pain thresholds across trials (they felt cold pain at higher temperatures). In addition, anxiety, depression, fatigue, and pain were related to decreased heat and cold pain thresholds in the overall sample. However, when group was controlled, none of these variables were related to thresholds or rates of habituation or sensitization. The differences between women with FM and healthy women in habituation and sensitization may have important implications for the etiology, diagnosis, and treatment of FM and other chronic pain conditions.     

Experimental muscle pain impairs descending inhibition

In chronic musculoskeletal pain conditions, the balance between supraspinal facilitation and inhibition of pain shifts towards an overall decrease in inhibition. Application of a tonic painful stimulus results in activation of diffuse noxious inhibitory controls (DNIC). The aims of the present experimental human study were (1) to compare DNIC, evoked separately, by hypertonic saline (6%)-induced muscle pain (tibialis anterior) or cold pressor pain; (2) to investigate DNIC evoked by concomitant experimental muscle pain and cold pressor pain, and (3) to analyze for gender differences. Ten males and 10 age matched females participated in two sessions. In the first session unilateral muscle pain or unilateral cold pressor pain were induced separately; in the second session unilateral muscle pain and unilateral cold pressor pain were induced concomitantly. Pressure pain thresholds (PPT) were measured around the knee joint before, during, and after DNIC induction. Cold pressor pain increased PPT in both males and females with greater increases in males. Hypertonic saline-evoked muscle pain significantly increased PPT in males but not in females. When cold pressor and muscle pain were applied concomitantly the PPT increases were smaller when compared to the individual sessions. This study showed for the first time that two concurrent conditioning tonic pain stimuli (muscle pain and cold pressor pain) cause less DNIC compared with either of the conditioning stimuli given alone; and males showed greater DNIC than females. This may explain why patients with chronic musculoskeletal pain have impaired DNIC.     

Quantitative sensory testing before and after regional guanethidine block in patients with neuralgia in the hand.

Using reference values from healthy volunteers, thermal and vibration-induced pain thresholds and the sensibility for warm and cold were studied in 18 patients with neuralgia in one hand following a traumatic injury or surgery. All patients had spontaneous pain and allodynia to vibration. They were treated with intravenous regional guanethidine block (RGB). Quantitative sensory testing was performed on both hands before and 1-3 days after treatment. Eleven patients benefitted considerably from the block, with pain relief for 2 weeks or more. Ten of these 11 patients had mild nerve injuries caused by compressive trauma to the nerve. Before RGB they showed a moderate loss in temperature discrimination capacity; their heat pain thresholds were reduced and they exhibited allodynia to cold and vibration on the injured side. After RGB, the pain thresholds were normalised both to thermal and vibratory stimuli. These patients were classified as having sympathetically maintained pain (SMP). Seven patients reported no or only minor pain-relieving effect of RGB lasting 1-5 days. Severe nerve injuries were most frequent in this group of patients. On the injured side, before RGB, their ability to discriminate between warm and cold was markedly impaired, thermal pain thresholds were normal, and they showed allodynia to vibration. After RGB, there was no change in thermal pain thresholds and the allodynia to vibration persisted. These patients were classified as having sympathetically independent pain (SIP). The results indicate that quantitative thermal sensory tests, together with clinical evaluation of the nerve trauma, can help to predict which patients will have long-lasting pain alleviation after RGB treatment.     

Patterns of quantitative sensation testing of hypoesthesia and hyperalgesia are predictive of diabetic polyneuropathy: a study of three cohorts. Nerve growth factor study group

OBJECTIVE: To test quantitative sensation testing (QST) patterns of hypoesthesia and hyperalgesia as indicators of diabetic polyneuropathy (DPN) and its severity RESEARCH DESIGN AND METHODS: We used Computer-Assisted Sensory Examination IV; characterized the QST results of the foot of each patient in three diabetic cohorts (approximately 1,500 patients) as hyperesthetic (< or = 2.5th percentile), low-normal (2.5th-50th percentiles), high-normal (50th-97.5th percentiles), or hypoesthetic (> or = 97.5th percentile); and tested associations with symptoms, impairments, and test abnormalities. RESULTS: Overall neuropathic impairment was most severe in the pancreas-renal transplant and nerve growth factor cohorts, but it was much less severe in the population-based Rochester Diabetic Neuropathy Study (RDNS) cohort. The frequency distribution of sensory abnormalities mirrored this difference. When the QST spectra of diabetic cohorts were compared with those of the control subject cohort for vibration and cooling sensations, the only abnormality observed was hypoesthesia, which was expressed as an increased number of subjects with values at or above the 97.5th percentile or by an increased percentage of cases with high-normal values. Symptoms and impairments of DPN were significantly more frequent in the subjects with values at or above the 97.5th percentile than in the subjects whose values were between the 50th and 97.5th percentiles. For heat pain (HP) sensation thresholds (intermediate pain severity [HP:5], pain threshold [HP:0.5], and pain-stimulus response slope [HP:5-0.5]), an increased frequency of both hypoalgesia and hyperalgesia was observed (especially in the RDNS cohort). Steeper pain-stimulus response slopes were significantly associated with sensory symptoms, including severity of pain. CONCLUSIONS: 1) Decreased vibratory sensation (hypoesthesia) appears to be characteristic of mild DPN, whereas panmodality hypoesthesia is characteristic of severe DPN. 2) A shift of vibratory and cold detection thresholds (and also of attributes of nerve conduction and a measure of autonomic dysfunction) from low-normal (2.5th-50th percentiles) to high-normal (50th-97.5th percentiles) appears to precede overt expression of DPN and to thereby provide evidence of subclinical abnormality 3) Heat stimulus-induced hyperesthesia (low thresholds) occurs especially in mild DPN, and, because it correlates with DPN symptoms and impairments, it must be attributed to hyperalgesia rather than to supersensitivity Therefore, hypoalgesia or hyperalgesia may be an indicator of early DPN.     

Thermal pain perception after aerobic exercise

OBJECTIVE: To examine thermal pain perception before, 5 minutes after, and 30 minutes after 30 minutes of treadmill exercise at 75% of maximal oxygen uptake (V o 2 max). DESIGN: Repeated-measures. SETTING: Sports science laboratory. PARTICIPANTS: Convenience sample of 14 healthy male and female volunteers (mean age +/- standard deviation, 32+/-3y). INTERVENTIONS: Sensory thresholds, pain thresholds, and pain ratings to hot and cold stimuli were measured before and after 30 minutes of treadmill exercise at 75% of V o 2 max. The hot and cold stimuli were delivered by using a thermode placed on the thenar eminence of the nondominant hand. Thermal sensory and pain thresholds were determined during continuous ramps in temperature of the thermode. MAIN OUTCOME MEASURES: Pain ratings were measured on a visual analog scale at 10-second intervals over 2 minutes of thermal pain stimulation. RESULTS: There were no significant changes in thermal sensitivity, pain thresholds, or pain ratings for either heat or cold after 30 minutes of exercise at 75% of V o 2 max. CONCLUSIONS: Pain perception to thermal stimuli was unaltered after 30 minutes of exercise at 75% of V o 2 max, an intensity and duration of exercise previously shown to alter pain perception to electric and mechanical stimuli.     

Hypersensitivity to pain in congenital blindness

Vision is important for avoiding encounters with objects in the environment that may imperil physical integrity. We tested whether, in the absence of vision, a lower pain threshold would arise from an adaptive shift to other sensory channels. We therefore measured heat and cold pain thresholds and responses to suprathreshold heat stimuli in 2 groups of congenitally blind and matched normal-sighted participants. We also assessed detection thresholds for innocuous warmth and cold, and participants’ attitude toward painful encounters in daily life. Our results show that, compared to sighted subjects, congenitally blind subjects have lower heat pain thresholds, rate suprathreshold heat pain stimuli as more painful, and have increased sensitivity for cold pain stimuli. Thresholds for nonpainful thermal stimulation did not differ between groups. The results of the pain questionnaires further indicated that blind subjects are more attentive to signals of external threats. These findings indicate that the absence of vision from birth induces a hypersensitivity to painful stimuli, lending new support to a model of sensory integration of vision and pain processing.     

Factor analysis of responses to thermal, electrical, and mechanical painful stimuli supports the importance of multi-modal pain assessment

During the last decade, a multi-modal approach has been established in human experimental pain research for assessing pain thresholds and responses to various experimental pain modalities. Studies have concluded that differences in responses to pain stimuli are mainly related to variation between individuals rather than variation in response to different stimulus modalities.In a factor analysis of 272 consecutive volunteers (137 men and 135 women) who underwent tests with different experimental pain modalities, it was determined whether responses to different pain modalities represent distinct individual uncorrelated dimensions of pain perception. Volunteers underwent single painful electrical stimulation, repeated painful electrical stimulation (temporal summation), test for reflex receptive field, pressure pain stimulation, heat pain stimulation, cold pain stimulation, and a cold pressor test (ice water test).Five distinct factors were found representing responses to 5 distinct experimental pain modalities: pressure, heat, cold, electrical stimulation, and reflex-receptive fields. Each of the factors explained approximately 8% to 35% of the observed variance, and the 5 factors cumulatively explained 94% of the variance. The correlation between the 5 factors was near null (median ρ = 0.00, range −0.03 to 0.05), with 95% confidence intervals for pairwise correlations between 2 factors excluding any relevant correlation. Results were almost similar for analyses stratified according to gender and age.Responses to different experimental pain modalities represent different specific dimensions and should be assessed in combination in future pharmacological and clinical studies to represent the complexity of nociception and pain experience.     

Differential physiological effects during tonic painful hand immersion tests using hot and ice water

The cold pressor test (CPT) is an empirically validated test commonly used in research on stress, pain and cardiovascular reactivity. Surprisingly, the equivalent test with water heated to noxious temperatures (hot water immersion test, HIT) has not been thoroughly investigated. The aim of the present study was to characterize the physiological effects and psychophysics of both tests and to analyze whether the autonomic responses are mainly induced by baroreflexes or a consequence of the pain experience itself. The study consisted of a single session including one CPT (4 ± 0.2 °C) and one HIT (47 ± 0.5 °C; cut‐off point 5 min) trial performed on 30 healthy drug free volunteers aged 19–57 (median 24) yrs. The sequence of both trials was alternated and participants were randomly assigned to sequence order and parallelized with respect to gender. Physiological parameters (cardiovascular, respiratory and electrodermal activity) and subjective pain intensity were continuously monitored. In addition, pain detection and tolerance thresholds as well as pain unpleasantness were assessed. Both tests were comparable with regard to the time course and intensity of subjective pain. However, a significantly higher increase of blood pressure could be observed during the CPT when compared to the HIT. The HIT appears less confounded with thermoregulatory baroreflex activity and therefore seems to be a more appropriate model for tonic pain.     

Differentiation of pain ratings in combat-related posttraumatic stress disorder

Although posttraumatic stress disorder (PTSD) is associated with chronic pain, preliminary evidence suggests reduced experimental pain sensitivity in this disorder. The questions addressed in the present study were whether pain perception would also be reduced in PTSD patients who are not suffering from chronic pain symptoms, and whether a reduction in pain sensitivity would also be present in combat veterans who did not develop PTSD. For this, we determined thermal detection and pain thresholds in 10 male combat-related PTSD patients, 10 combat control subjects (no PTSD) and 10 healthy controls without combat experience. All subjects were pain free. First, we measured thermal sensory thresholds with ramped heat and cold stimuli using the method of limits. Ramped thermal sensory stimulation revealed no deficits for the detection of (non-noxious) f2.1thermal stimuli between groups. In contrast, heat and cold pain thresholds in both combat groups (PTSD and combat controls) were significantly increased compared to healthy controls. However, these stimuli could not distinguish between the two groups due to ceiling effects. When using longer-lasting heat stimulation at different temperatures (30 s duration; method of fixed stimuli), we found significantly lower frequency of pain reports in PTSD patients compared with both combat and healthy controls, as well as significantly lower pain ratings. Our results suggest an association of PTSD with reduced pain sensitivity, which could be related to PTSD-related (neuro-)psychological alterations or to a pre-existing risk factor for the disorder.     

Age effects on pain thresholds, temporal summation and spatial summation of heat and pressure pain

Experimental data on age-related changes in pain perception have so far been contradictory. It has appeared that the type of pain induction method is critical in this context, with sensitivity to heat pain being decreased whereas sensitivity to pressure pain may be even enhanced in the elderly. Furthermore, it has been shown that temporal summation of heat pain is more pronounced in the elderly but it has remained unclear whether age differences in temporal summation are also evident when using other pain induction methods. No studies on age-related changes in spatial summation of pain have so far been conducted. The aim of the present study was to provide a comprehensive survey on age-related changes in pain perception, i.e. in somatosensory thresholds (warmth, cold, vibration), pain thresholds (heat, pressure) and spatial and temporal summation of heat and pressure pain. We investigated 20 young (mean age 27.1 years) and 20 elderly (mean age 71.6 years) subjects. Our results confirmed and extended previous findings by showing that somatosensory thresholds for non-noxious stimuli increase with age whereas pressure pain thresholds decrease and heat pain thresholds show no age-related changes. Apart from an enhanced temporal summation of heat pain, pain summation was not found to be critically affected by age. The results of the present study provide evidence for stimulus-specific changes in pain perception in the elderly, with deep tissue (muscle) nociception being affected differently by age than superficial tissue (skin) nociception. Summation mechanisms contribute only moderately to age changes in pain perception.     

Reference values for quantitative sensory testing in children and adolescents: Developmental and gender differences of somatosensory perception

The Quantitative Sensory Testing (QST) protocol of the German research network on neuropathic pain (DFNS) encompassing all somatosensory modalities assesses the functioning of different nerve fibers and of central pathways. The aim of our study was: (1) to explore, whether this QST protocol is feasible for children, (2) to detect distribution properties of QST data and the impact of body site, age and gender and (3) to establish reference values for QST in children and adolescents. The QST protocol of the DFNS with modification of instructions and pain rating was used in 176 children aged 6.12–16.12 years for six body sites. QST was feasible for children over 5 years of age. ANOVAs revealed developmental, gender and body site differences of somatosensory functions similar to adults. The face was more sensitive than the hand and/or foot. Younger children (6–8 years) were generally less sensitive to all thermal and mechanical detection stimuli but more sensitive to all pain stimuli than older (9–12 years) children, whereas there were little differences between older children and adolescents (13–17 years). Girls were more sensitive to thermal detection and pain stimuli, but not to mechanical detection and pain stimuli. Reference values differ from adults, but distribution properties (range, variance, and side differences) were similar and plausible for statistical factors. Our results demonstrate that the full QST protocol is feasible and valid for children over 5 years of age with their own reference values.     

Quantitative sensory testing: a comprehensive protocol for clinical trials.

We have compiled a comprehensive QST protocol as part of the German Research Network on Neuropathic Pain (DFNS) using well established tests for nearly all aspects of somatosensation. This protocol encompasses thermal as well as mechanical testing procedures. Our rationale was to test for patterns of sensory loss (small and large nerve fiber functions) or gain (hyperalgesia, allodynia, hyperpathia), and to assess both cutaneous and deep pain sensitivity. The practicality of the QST protocol was tested in 18 healthy subjects, 21-58 years, half of them female. All subjects were tested bilaterally over face, hand and foot. We determined thermal detection and pain thresholds including a test for the presence of paradoxical heat sensations, mechanical detection thresholds to von Frey filaments and a 64-Hz tuning fork, mechanical pain thresholds to pinprick stimuli and blunt pressure, stimulus-response-functions for pinprick and dynamic mechanical allodynia (pain to light touch), and pain summation (wind-up ratio) using repetitive pinprick stimulation. The full protocol took 27+/-2.3 min per test area. The majority of QST parameters were normally distributed only after logarithmic transformation (secondary normalization) except for the frequency of paradoxical heat sensations, cold and heat pain thresholds, and for vibration detection thresholds. Thresholds were usually lowest over face, followed by hand, and then foot. Only thermal pain thresholds, wind-up ratio and vibration detection thresholds were not significantly dependent on the body region. There was no significant right-to-left difference for any of the QST parameters; left-to-right correlation coefficients ranged between 0.78 and 0.97, thus explaining between 61% and 94% of the variance. This study has shown that a complete somatosensory profile of one affected area and one unaffected control area, which will be necessary to characterize patients with a variety of diseases, can be obtained within 1 h. Case examples of selected patients illustrate the value of z-transformed QST data for an easy survey of individual symptom profiles.     

Does a regional nerve block change cutaneous perception thresholds outside the anaesthetic area? Implications for the interpretation of diagnostic blocks.

The present study was performed on pain-free subjects and patients to analyse if local anaesthetics (LA) normally used for nerve blocks in the orofacial region resulted in generalised changes in cutaneous somatosensory perception thresholds outside the territory of the primarily blocked nerve. Five subjects received an intra-oral nerve block and 5 patients received epidural anaesthesia, serving as a reference group considering the larger amounts of LA used in this latter type of anaesthesia. No differences (after vs. prior to LA) were detected regarding thresholds to tactile, cold, warmth or heat pain stimuli in skin areas outside the regions directly blocked. This was also true for the difference limens between warm-cold thresholds. Our data do not indicate any generalised influence on tactile, thermal and pain perception thresholds in pain-free subjects.     

Psychophysical study of the effects of topical application of menthol in healthy volunteers

Cold hyperalgesia is a major clinical phenomenon, but validated experimental models are still lacking for humans. Topical menthol application has recently been proposed as a possible model for the study of cold pain. We characterized the psychophysical effects of 30% l-menthol in ethanol on glabrous skin in 39 healthy subjects, using a double-blind, randomized, crossover design, with ethanol as a control. Psychophysical testing included an assessment of pain thresholds and detection of mechanical, cold, and heat stimuli, and of the sensations induced by suprathreshold stimuli. Most subjects (90%) perceived a cooling sensation with menthol. Menthol decreased cold pain thresholds and enhanced pain responses to suprathreshold noxious cold stimuli, without affecting responses to other stimuli. Menthol therefore has selective effects on noxious cold processing. No subject displayed signs of skin irritation or redness. These data suggest that 30% menthol application may be a useful experimental model for studies of cold hyperalgesia in humans. The absence of local skin reactions also makes this test potentially suitable for use in patients.     

Somatosensory function in patients with and without pain after traumatic peripheral nerve injury

Why traumatic injuries to the peripheral nervous system infrequently result in neuropathic pain is still unknown. The aim of this study was to examine the somatosensory system in patients with traumatic peripheral nerve injury with and without pain to try to unravel possible links to mechanisms underlying development and maintenance of pain. Eighteen patients with spontaneous ongoing pain and 16 patients without pain after unilateral partial peripheral traumatic nerve injury were studied. In the area of partial denervation and in the corresponding contralateral area perception thresholds to warmth, cold, light touch, pressure pain, cold‐ and heat pain were assessed as were pain intensities at suprathreshold heat pain stimulation. Comparing sides patients with pain reported allodynia to cold (p = 0.03) and pressure (p = 0.016) in conjunction with an increase in the perception threshold to non‐painful warmth (p = 0.024) on the injured side. Pain‐free patients reported hypoesthesia to light touch (p = 0.002), cold (p = 0.039) and warmth (p = 0.001) on the injured side. There were no side differences in stimulus–response functions using painful heat stimuli in any of the groups. In addition, no significant difference could be demonstrated in any sensory modality comparing side‐to‐side differences between the two groups. In conclusion, increased pain sensitivity to cold and pressure was found on the injured side in pain patients, pointing to hyperexcitability in the pain system, a finding not verified by a more challenging analysis of side‐to‐side differences between patients with and without pain.     

Widespread sensory hypersensitivity is a feature of chronic whiplash-associated disorder but not chronic idiopathic neck pain

OBJECTIVES: To investigate sensory changes present in patients with chronic whiplash-associated disorders and chronic idiopathic neck pain using a variety of quantitative sensory tests to better understand the pain processing mechanisms underlying persistent symptoms. METHODS: A case control study was used with 29 subjects with chronic whiplash-associated disorders, 20 subjects with chronic idiopathic neck pain, and 20 pain-free volunteers. Pressure pain thresholds were measured over the articular pillars of C2-C3, C5-C6, the median, radial, and ulnar nerve trunks in the arm and over a remote site, the muscle belly of tibialis anterior. Heat pain thresholds, cold pain thresholds, and von Frey hair sensibility were measured over the cervical spine, tibialis anterior, and deltoid insertion. Anxiety was measured with the Short-Form of the Spielberger State Anxiety Inventory. RESULTS: Pressure pain thresholds were decreased over cervical spine sites in both subject groups when compared with controls (P < 0.05). In the chronic whiplash-associated disorders group, pressure pain thresholds were also decreased over the tibialis anterior, median, and radial nerve trunks (P < 0.001). Heat pain thresholds were decreased and cold pain thresholds increased at all sites (P < 0.03). No differences in heat pain thresholds or cold pain thresholds were evident in the idiopathic neck pain group at any site compared with the control group (P > 0.27). No abnormalities in von Frey hair sensibility were evident in either neck pain group (P > 0.28). DISCUSSION: Both chronic whiplash-associated disorders and idiopathic neck pain groups were characterized by mechanical hyperalgesia over the cervical spine. Whiplash subjects showed additional widespread hypersensitivity to mechanical pressure and thermal stimuli, which was independent of state anxiety and may represent changes in central pain processing mechanisms. This may have implications for future treatment approaches.     

Thermal and tactile perception thresholds in acute herpes zoster

This study was conducted to determine somatosensory perception thresholds in 97 immunocompetent patients with herpes zoster (HZ), and to evaluate their associations with the development of post-herpetic neuralgia (PHN). Warm, cold and heat pain thresholds were tested by Thermotest (SOMEDIC) and tactile thresholds by Semmes-Weinstein monofilaments. To establish reference values, 103 healthy subjects underwent somatosensory testing, from which values were calculated for both genders for four age groups (<60, 60–69, 70–79 and ≥ in five dermatomal levels (VI, C3, T3, T10 and S1). Patients with HZ underwent quantitative somatosensory testing within the affected dermatome, its mirror image dermatome and an adjacent dermatome bilaterally. The follow-up visits with somatosensory testing took place at 2 weeks, 6 weeks, 3 months and 6 months. When evaluated as means of the results, warm and cold thresholds were significantly elevated in the affected dermatome from the initial visit until 3 and 6 months, respectively. By contrast, heat pain thresholds were lowered at the initial visit but normalized by 2 weeks, and tactile thresholds remained unchanged. These threshold changes were associated neither with further development of PHN nor each other. It is concluded that measurement of somatosensory perception thresholds in early stages of HZ shows evidence of impaired neural function but is not helpful in predicting which patient will go on to develop PHN.