Quantitative sensory testing

Sensory perception and neuroanatomical structures in normal and grafted skin of burn survivors

BACKGROUND

This study compared the neural structures found in grafted skin of burn survivors with neural structures found in site-matched normal skin and correlated these structures with psychophysical measures of sensation.

METHODS

Fifteen skin-grafted male burn survivors (47.7+/-10.4 years old) with deep partial- or full-thickness thermal burn injuries covering an average of 11+/-5.6% of their total body surface and with normal skin at a matching, unburned, contralateral site were recruited into this study. Threshold determinations and magnitude estimations for touch, cold, warmth and heat-pain were performed at sites with grafted and normal skin, using Semmes-Weinstein monofilaments and the Medoc TSA 2001 thermal stimulator. Skin biopsies from both the grafted and normal sites were stained with antibodies for protein gene product 9.5 (PGP) and neurofilament 200 kDa. Nerve fibers in the epidermis and nerve fibers or bundles of nerve fibers in the superficial and deep dermis as well as innervated blood vessels, hair follicles and sweat glands were counted.

RESULTS

On average, the data were collected 43.1+/-10.4 months after grafting. When thresholds on grafted skin were compared to thresholds on normal skin, they showed elevated sensory thresholds [touch (p<0.003), cold (p<0.031), warmth (p<0.009)]. Magnitude estimates of touch, cold and warmth differed on the two sides with sensations elicited from grafts being smaller than those from normal skin. Heat-pain thresholds and heat-pain magnitude estimations were not statistically different on the two sites. By comparison to the normal side, and consistent with the attenuated sensory functions of the grafts, counts of neural structures showed a reduction in innervation density; PGP-immunoreactive nerve fibers/bundles were reduced in grafted epidermis (p<0.026) and superficial dermis (p<0.001). The numbers of sweat glands (p<0.006) and hair follicles (p<0.001) were also reduced. The number of innervated blood vessels did not differ significantly on the two sides. There were significant correlations between sensory thresholds and the neuroanatomical variables: thresholds of cold and touch were correlated with the number of sweat glands in both grafted and normal skin (r2=0.56 and 0.50, respectively; p<0.001), while warmth thresholds were significantly correlated with the number of innervated blood vessels in grafted skin (r2=0.62, p<0.001). Encapsulated mechanoreceptors were not encountered in this study of hairy skin.

CONCLUSIONS

Touch, cold and warmth thresholds and magnitude estimations do not return to normal levels after skin grafting in burn survivors. The elevation of thresholds and reduction of sensory intensity is accompanied by a general decrease in the density of nerve terminals. The lack, or numerical reduction, of sweat glands and innervated blood vessels was also indicative of diminished sensation on grafted skin.

Quantitative thermal sensory testing — value of testing for both cold and warm sensation detection in evaluation of small fiber neuropathy

OBJECTIVE

Small fiber neuropathy is a common neurological disorder, often missed or ignored by physicians, since examination and routine nerve conduction studies are usually normal in this condition. Many methods including quantitative thermal sensory testing are currently being used for early detection of this condition, so as to enable timely investigation and treatment. This study was conducted to assess the yield of quantitative thermal sensory testing in diagnosis of small fiber neuropathy.

MATERIAL AND METHODS

We included patients presenting with history suggestive of positive and/or negative sensory symptoms, with normal examination findings, clinically suggestive of small fiber neuropathy, with normal or minimally abnormal routine nerve conduction studies. These patients were subjected to quantitative thermal sensory testing using a Medoc TSA-II Neurosensory analyser at two sites and for two modalities. QST data were compared with those in 120 normal healthy controls.

RESULTS

Twenty-five patients (16 males, 9 females) with mean age 46.8+/-16.6 years (range: 21-75 years) were included in the study. The mean duration of symptoms was 1.6+/-1.6 years (range: 3 months-6 years). Eighteen patients (72%) had abnormal thresholds in at least one modality. Thermal thresholds were normal in 7 out of the 25 patients.

CONCLUSION

This study demonstrates that quantitative thermal sensory testing is a fairly sensitive method for detection of small fiber neuropathy especially in patients with normal routine nerve conduction studies.

Clinical spectrum of cryoglobulinaemic neuropathy

BACKGROUND AND OBJECTIVE

Cryoglobulinaemic neuropathy (CN) is probably common, as it is usually related to HCV infection. The aim of this study was to delineate the clinical spectrum of CN in a large series and to investigate the factors influencing its expression.

METHODS

Seventy one consecutive patients (12 men, 59 women), diagnosed as having CN on the basis of clinical features of neuropathy, clinical and serological findings of mixed cryoglobulinaemia, and exclusion criteria, were identified during a six year period. All patients underwent clinical examination, and electrophysiological and laboratory investigations.

RESULTS

Results of the patients with "pure" CN (n = 54) and those with comorbidities (n = 17) were evaluated separately. Of the former 76% had sensory neuropathy (including selective small fibre sensory neuropathy (SFSN) in 14 patients), 15% had sensorimotor polyneuropathy, and 9% had mononeuritis multiplex. The pattern of distribution was similar in the patients with comorbidities. In 30/54 patients, CN was the first manifestation of cryoglobulinaemia. Patients with mild cryoglobulinaemic syndrome had sensory neuropathy more frequently than patients with active syndrome (p < 0.001), in particular SFSN (p < 0.001). The latter group had more severe features, with significantly more cases of reduced or absent motor (p = 0.028) and sensory action potentials (p < 0.001), and a tendency towards higher Rankin scores (p = 0.06).

CONCLUSIONS

Sensory neuropathy, often in the form of SFSN, is by far the commonest form of CN. Cryoglobulinaemia should be vigorously investigated in the diagnosis of sensory neuropathy, especially in older women. Activity of the cryoglobulinaemic syndrome is a major factor influencing the clinical expression and severity of CN.

Psychological factors associated with perception of experimental pain in vulvar vestibulitis syndrome

This study assessed the association between pain perception and psychological variables in women with vulvar vestibulitis syndrome (VVS) by comparing 28 VVS women with 50 healthy women. We assessed non genital systemic pain perception with quantitative sensory testing by administering experimental pain stimuli to the forearm. The VVS women demonstrated a lower pain threshold and a higher magnitude estimation of pain, combined with a higher trait anxiety, increased somatization, and a lower body image. Among the VVS women, nonvaginal pain catastrophizing was significantly related to reported pain during coitus. A cluster analysis revealed four subtypes of VVS women, as characterized by levels of pain and personality variables. I suggest implications for the assessment and treatment of women suffering from painful coitus.

Vagal stomach afferents inhibit somatic pain perception

Vagal stimulation inhibits systemic pain perception in animals, probably via the nucleus tractus solitarius and its connections with descending nuclei in the brainstem which inhibit pain. Pain-inhibiting effects of such stimulation in humans, obtained from epileptic patients treated by vagal stimulation, are controversial. The aim of our study was to evaluate whether vagal stomach afferent activation inhibits pain perception in healthy humans. Pain thresholds, magnitude of tonic heat pain at 46 degrees C stimulation, pain temporal summation and laser pain evoked potentials were measured at the hand before and immediately after rapid drinking of 1500 ml water in 31 volunteers. We found an increase in heat pain threshold from 43.3+/-2.6 to 44.7+/-2.2 degrees C, P<0.0001, a decrease of peak pain magnitude to tonic heat from 56.3+/-26.2 to 43.7+/-25.8 (on 0-100 VAS), P<0.0001, a lowering of area under the curve during tonic noxious heat stimulus from 1962+/-984 to 1411+/-934, P<0.001. Additionally, we observed a decrease in the peak to peak evoked potential amplitude from 19.2 microV+/-1.2 to 15.6 microV+/-1.2 (P=0.005) together with a decrease in the estimation of mean laser induced pain from 52.28+/-18.00 to 48.14+/-20.18 (P=0.025). Mechanical pain thresholds and temporal summation did not change significantly. We conclude that vagal stomach afferents exert an inhibitory effect on somatic pain perception in humans.

Personality traits associated with perception of noxious stimuli in women with vulvar vestibulitis syndrome

Vulvar vestibulitis syndrome (VVS) is associated with enhanced pain sensitivity. The present study explores the role of personality on the perception of noxious stimuli among women with VVS. More specifically, the aim of the study was to explore whether the personality traits assessed by Cloninger's Tridimensional Personality Questionnaire (TPQ) (harm avoidance [HA], novelty seeking [NS], and reward dependence [RD]) are associated with the augmented pain perception in women with VVS. Quantitative sensory tests were applied to the forearm of 98 women with VVS and 135 control subjects, all of whom completed the TPQ. The women with VVS scored higher than the control subjects on HA and RD with no significant differences in NS. Linear regression analyses revealed that in the VVS group, lower pain thresholds and higher magnitude estimations of suprathreshold pain stimuli were associated with higher HA and RD scores. The enhanced pain perception among women with VVS might reflect their tendency to respond intensely to signals of reward and to elevate the perceived risk. This might lead them to avoid hazards by overestimating the level of potential harm, as represented by greater pain sensitivity. The association between personality traits assessed by Cloninger's Tridimensional Personality Questionnaire, ie, harm avoidance, novelty seeking, and reward dependence, and the enhanced perception of noxious stimuli in vulvar vestibulitis syndrome might suggest neurochemical mechanisms of pain experience affected by personality, with possible application for future treatment approaches toward pain disorders.

Can diabetic neuropathy be prevented?

The incidence of diabetes and its complication have rapidly increased. Decreased quality of life and increased mortality are the major problems of people with diabetes. These problems are mainly caused by chronic complications. The incidence of diabetic neuropathy, which is one of these chronic complications, approaches 50% in most diabetic patients. The intensive metabolic management alone cannot completely prevent the development and progression of diabetic complications. Therefore, blocking and management of pathogenic mechanism of complication are required. Pathogenesis of diabetic neuropathy has multifactorial causes. Diabetic neuropathy is thought to occur both from direct hyperglycemia-induced damage to the nerve parenchyma and from neuronal ischemia brought about indirectly by hyperglycemia-induced decreases in neurovascular flow. The effects of hyperglycemia get converted to neuronal dysfunction via at least three secondary biochemical pathways: the polyol pathway, non-enzymatic glycation of proteins, oxidative stress and protein kinase C, and the interactions between them. Because of these interactions, interference with one of these biochemical pathways could either worsen or attenuate the effects of the others. So, the use of therapeutic intervention of these pathways is inevitable and valid to prevent the progression of diabetic neuropathy. As yet, a satisfactory and fundamental, preventive, and therapeutic method is not available with us to prevent progression. So, we will introduce the earlier diagnostic methods of diabetic neuropathy and will discuss the advantages and limitations of each method.

Small fiber neuropathy: a common and important clinical disorder

Small fiber neuropathy (SFN) is a neuropathy selectively involving small diameter myelinated and unmyelinated nerve fibers. Interest in this disorder has considerably increased during the past few years. It is often idiopathic and typically presents with peripheral pain and/or symptoms of autonomic dysfunction. Diagnosis is made on the basis of the clinical features, normal nerve conduction studies (NCS) and abnormal specialized tests of small nerve fibers. Among others, these tests include assessment of epidermal nerve fiber density, temperature sensation tests for sensory fibers and sudomotor and cardiovagal testing (QSART) for autonomic fibers. Unless an underlying disease is identified, treatment is usually symptomatic and directed towards alleviation of neuropathic pain.

Seasonal changes in thermal responses of urban residents to cold exposure

To determine whether urban circumpolar residents show seasonal acclimatisation to cold, thermoregulatory responses and thermal perception during cold exposure were examined in young men during January-March (n=7) and August-September (n=8). Subjects were exposed for 24 h to 22 and to 10 degrees C. Rectal (T(rect)) and skin temperatures were measured throughout the exposure. Oxygen consumption (VO(2)), finger skin blood flow (Q(f)), shivering and cold (CDT) and warm detection thresholds (WDT) were assessed four times during the exposure. Ratings of thermal sensations, comfort and tolerance were recorded using subjective judgement scales at 1-h intervals. During winter, subjects had a significantly higher mean skin temperature at both 22 and 10 degrees C compared with summer. However, skin temperatures decreased more at 10 degrees C in winter and remained higher only in the trunk. Finger skin temperature was higher at 22 degrees C, but lower at 10 degrees C in the winter suggesting an enhanced cold-induced vasoconstriction. Similarly, Q(f) decreased more in winter. The cold detection threshold of the hand was shifted to a lower level in the cold, and more substantially in the winter, which was related to lower skin temperatures in winter. Thermal sensations showed only slight seasonal variation. The observed seasonal differences in thermal responses suggest increased preservation of heat especially in the peripheral areas in winter. Blunted vasomotor and skin temperature responses, which are typical for habituation to cold, were not observed in winter. Instead, the responses in winter resemble aggravated reactions of non-cold acclimatised subjects.

The evaluation of small fiber function-autonomic and quantitative sensory testing

Disorders of the autonomic and small nerve fibers comprise a wide spectrum of disease states that cross a multitude of clinical specialties.The evaluation of these disorders allows the investigator to determine the presence or absence of abnormalities in the lightly myelinated and unmyelinated nerve fibers with minimal discomfort to the patient. The severity of dysfunction also can be determined to guide therapy and aid in prognostication for individual patients.

Cooling detection thresholds in the assessment of diabetic sensory polyneuropathy: comparison of CASE IV and Medoc instruments

OBJECTIVE

Cooling detection threshold testing may be an important quantitative method for assessing polyneuropathy, in that it has traditionally been viewed as a measure of small-fiber involvement. The present study sought to determine the agreement between two common testing devices and to determine whether these are concordant in their association with predictor variables for diabetic sensory polyneuropathy.

RESEARCH DESIGN AND METHODS

A total of 83 patients with diabetes (10 patients with type 1 diabetes and 73 patients with type 2 diabetes) and a wide spectrum of diabetic sensory polyneuropathy severity underwent concurrent cooling detection threshold testing using the Medoc and CASE IV instruments. Common predictor variables for diabetic sensory polyneuropathy were measured on the same day.

RESULTS

Measurements of cooling detection thresholds by both instruments were highly correlated (Spearman's correlation coefficient 0.81, P < 0.001) and demonstrated a high degree of agreement by the method of Bland and Altman (95% distribution critical values for the difference in cooling detection thresholds, +7.5 and -5.6 degrees C). Cooling detection thresholds by both instruments were strongly correlated with clinical indicators of large-fiber neuropathy but not with the symptoms of small-fiber neuropathy (pain).

CONCLUSIONS

These two instruments available for assessment of cooling detection thresholds are interchangeable for research in diabetic sensory polyneuropathy. However, this modality is equivalent to other modalities of quantitative sensory threshold testing in its association with indicators of large-fiber neuropathy and does not seem to provide an advantage for the prediction of small-fiber involvement.

Effects of surgery on the sensory deficits of syringomyelia and predictors of outcome: a long term prospective study

OBJECTIVE

To quantify the effects of surgery on the thermal deficits of syringomyelia and assess the predictors for such effects.

METHODS

The subjects were 16 consecutive patients (12 men, 4 women; mean (SD) duration of sensory symptoms, 5.1 (4.5) years) presenting with the typical symptoms of syringomyelia related to Chiari I malformation or trauma, and requiring surgical treatment. They were evaluated before surgery, then at six months and two years. Sensory evaluation included determination of the extent of thermal deficits and quantitative assessment of thermal, mechanical, vibration detection, and pain thresholds. Neuropathic pain intensity was evaluated on visual analogue scales. Magnetic resonance imaging was done before and after surgery to measure syrinx dimensions.

RESULTS

The magnitude and extent of thermal deficits improved in a subgroup of patients and this was best predicted by the duration of sensory symptoms: patients operated on less than two years after the onset of their symptoms tended to improve, while those operated on later were stabilised or deteriorated slightly. The effect of surgery on thermal deficits was correlated with the duration of sensory symptoms. Surgery also affected vibration deficits in patients with the Chiari malformation, neuropathic pain on effort, and syrinx dimensions.

CONCLUSIONS

The duration of sensory deficits is the best predictive factor of the efficacy of surgery for the thermal symptoms of syringomyelia. Early surgery is required if these deficits are to be minimised.

Quantitative vibration threshold testing in carpal tunnel syndrome: analysis strategies for optimizing reliability

Tuning forks and electronic vibrometers have been used to quantify vibration sensation thresholds, which are thought to be affected early in carpal tunnel syndrome (CTS). The purpose of this study was to identify a reliable testing procedure for a newly designed, computer-controlled vibrometer (PCV50; Ztech, Salt Lake City, UT). Fifty-two patients (mean age 48+/-8 years) with electromyographically confirmed CTS were tested on one occasion. The computer-controlled vibrometer, with a fixed frequency of 50 Hz, used stepwise changes in amplitude to determine vibration sensation threshold. Each patient had three vibrometer measures (trials) taken on the pulp of the third digit of their right and left hands during the first test session and were retested by a single repetition 40 to 60 minutes later (retest). Intraclass correlation coefficients (ICCs) were used to examine several data analysis strategies. The strategy that generated the highest ICCs for both the right and left hands assumed that the first trial was a learning or practice attempt, and compared the average of the second and third trials with the score from the second session (ICC=0.86 and 0.89, respectively). The computer-controlled vibrometer offered an easily administered, quantitative, and comfortable means to assess median nerve function. Using this reliable testing procedure will allow for additional investigations to determine its usefulness in the early detection and accurate quantification of CTS-related impairment.

Development and validation of the Neuropathic Pain Symptom Inventory

This study describes the development and validation of the Neuropathic Pain Symptom Inventory (NPSI), a new self-questionnaire specifically designed to evaluate the different symptoms of neuropathic pain. Following a development phase and a pilot study, we generated a list of descriptors reflecting spontaneous ongoing or paroxysmal pain, evoked pain (i.e. mechanical and thermal allodynia/hyperalgesia) and dysesthesia/paresthesia. Each of these items was quantified on a (0-10) numerical scale. The validation procedure was performed in 176 consecutive patients with neuropathic pain of peripheral (n = 120) or central (n = 56) origin, recruited in five pain centers in France and Belgium. It included: (i) assessment of the test-retest reliability of each item, (ii) determination of the factorial structure of the questionnaire and analysis of convergent and divergent validities (i.e. construct validity), and (iii) evaluation of the ability of the NPSI to detect the effects of treatment (i.e. sensitivity to change). The final version of the NPSI includes 10 descriptors (plus two temporal items) that allow discrimination and quantification of five distinct clinically relevant dimensions of neuropathic pain syndromes and that are sensitive to treatment. The psychometric properties of the NPSI suggest that it might be used to characterize subgroups of neuropathic pain patients and verify whether they respond differentially to various pharmacological agents or other therapeutic interventions.

Chemotherapy-evoked painful peripheral neuropathy

Vincristine and paclitaxel, two of the most effective drugs in the battle against cancer, produce a dose-limiting neurotoxicity that sometimes presents as a painful peripheral neuropathy. For the first time, investigators have been able to produce these chemotherapy-evoked painful peripheral neuropathies in the laboratory rat. These new models have already begun to elucidate the causes of the neuropathic pain associated with these antineoplastic drugs, which will now make it possible to search for effective ways to prevent and treat it.

[Neuropathic pain: experimental advances and clinical applications]

Neuropathic pain is a clinical entity designating the different types of pain associated with a lesion of the nervous system including a wide range of pathological conditions from painful peripheral lesions (for example diabetic neuropathy, post-zoster pain, trauma-induced nerve injury) and central pain (particularly stroke-induced pain, spinal lesions, and multiple sclerosis). Despite this wide range of etiologies, neuropathic pain has well characterized clinical features which generally allow distinction from other types of pain: continuous often burn-like pain, paroxysmal pain (electrical discharge, knife stab), evoked pain, highly invalidating pain (allodynia, hyperalgesia), and associated dysethesia and/or paresthesia. Over the last ten Years, very little work has been published on neuropathic pain, which is now becoming a very active domain of research in neurobiology. Advances to date have not been spectacular although better tolerated agents have been recently marketed. Future progress should enable an appropriate response to the therapeutic challenge of neuropathic pain.

Skin denervation in type 2 diabetes: correlations with diabetic duration and functional impairments

Sensory neuropathy is a prominent component of diabetic neuropathy. It is not entirely clear how diabetes influences skin innervation, and whether these changes are correlated with clinical signs and laboratory findings. To investigate these issues, we performed skin biopsies on the distal leg of 38 consecutive type 2 diabetic patients with sensory symptoms in lower limbs (25 males and 13 females, aged 56.2 +/- 9.4 years) and analysed the correlations of intraepidermal nerve fibre (IENF) densities in skin with glycaemic status (duration of diabetes, HbA1C, and fasting and post-prandial glucose levels), and functional parameters of small fibres (warm and cold thresholds) and large fibres (vibratory threshold and parameters of nerve conduction studies). Clinically, 23 patients (60.5%) had signs of small-fibre impairment, and 19 patients (50.0%) had signs of large-fibre impairment. IENF densities were much lower in diabetic patients than in age- and gender-matched controls (1.794 +/- 2.120 versus 9.359 +/- 3.466 fibres/mm, P < 0.0001), and 81.6% (31/38) of diabetic patients had reduced IENF densities. IENF densities were negatively associated with the duration of diabetes (standardized coefficient: -0.422, P = 0.015) by analysis with a multivariate linear regression model. Abnormal results of functional examinations were present in 81.6% (warm threshold), 57.9% (cold threshold), 63.2% (vibratory threshold) and 49% (amplitude of sural sensory action potential) of diabetic patients. Among the three sensory thresholds, the warm threshold temperature had the highest correlation with IENF densities (standardized coefficient: -0.773, P < 0.0001). On nerve conduction studies in lower-limb nerves, there were abnormal responses in 54.1% of sural nerves, and 50.0% of peroneal nerves. Of neurophysiological parameters, the amplitude of the sural sensory action potential had the highest correlation with IENF density (standardized coefficient: 0.739, P < 0.0001). On clinical examination, 15 patients showed no sign of small-fibre impairment, but seven of these patients had reduced IENF densities. In conclusion, small-fibre sensory neuropathy presenting with reduced IENF densities and correlated elevation of warm thresholds is a major manifestation of type 2 diabetes. In addition, the extent of skin denervation increases with diabetic duration.

Vulvar vestibulitis severity—assessment by sensory and pain testing modalities

Vulvar vestibulitis syndrome (VVS) is a common cause of dyspareunia in pre-menopausal women. Previous quantitative sensory test (QST) studies have demonstrated reduced vestibular pain thresholds in these patients. Here we try to find whether QST findings correlate to disease severity. Thirty-five vestibulitis patients, 17 with moderate and 18 with severe disorder, were compared to 22 age matched control women. Tactile and pain thresholds for mechanical pressure and thermal pain were measured at the posterior fourcette. Magnitude estimation of supra-threshold painful stimuli were obtained for mechanical and thermal stimuli, the latter were of tonic and phasic types. Pain thresholds were lower and supra-threshold magnitude estimations were higher in VVS patients, in agreement with disease severity. Cut-off points were defined for results of each test, discriminating between moderate VVS, severe VVS and healthy controls, and allowing calculation of sensitivity and specificity of the various tests. Our findings show that the best discriminative test was mechanical pain threshold obtained by a simple custom made 'spring pressure device'. This test had the highest kappa value (0.82), predicting correctly 88% of all VVS cases and 100% of the severe VVS cases. Supra-threshold pain magnitude estimation for tonic heat stimulation also had a high kappa value (0.73) predicting correctly 82% overall with a 100% correct diagnosis of the control group. QST techniques, both threshold and supra-threshold measurements, seem to be capable of discriminating level of severity of this clinical pain syndrome.

Enzyme replacement therapy improves peripheral nerve and sweat function in Fabry disease

Fabry disease is an X-linked disorder caused by a deficiency of lysosomal alpha-galactosidase A resulting in accumulation of alpha-D-galatosyl conjugated glycosphingolipids. Clinical manifestations include a small-fiber neuropathy associated with debilitating pain and hypohidrosis. We report the effect of a 3-year open-label extension of a previously reported 6-month placebo-controlled enzyme replacement therapy (ERT) trial in which 26 hemizygous patients with Fabry disease received 0.2 mg/kg of alpha-galactosidase A every 2 weeks. The effect of ERT on neuropathic pain scores while off pain medications, quantitative sensory testing, quantitative sudomotor axon reflex test (QSART), and thermoregulatory sweat test (TST) is reported. In the patients who crossed-over from placebo to ERT (n = 10), mean pain-at-its-worst scores on a 0-10 scale decreased (from 6.9 to 4.5). There was a significant reduction in the threshold for cold and warm sensation in the foot. At the 3-year time-point, pre-ERT sweat excretion in 17 Fabry patients was 0.24 +/- 0.33 microl/mm(2) vs. 1.05 +/- 0.81 in concurrent controls (n = 38). Sweat function improved 24-72 h post-enzyme infusion (0.57 +/- 0.71 microl/mm(2)) and normalized in four anhidrotic patients. TST confirmed the QSART results. We conclude that prolonged ERT in Fabry disease leads to a modest but significant improvement in the clinical manifestations of the small-fiber neuropathy associated with this disorder. QSART may be useful to further optimize the dose and frequency of ERT.

Subclinical sensory abnormalities in trigeminal neuralgia

Trigeminal neuralgia is considered as a paroxysmal single nerve phenomenon. Abnormal sensory perception has been previously described in 15-25% of patients with clinical examination. Quantitative sensory testing (QST) was used to evaluate sensory perception in patients with idiopathic trigeminal neuralgia (ITN). Nine patients and 10 normal control subjects were evaluated in all six trigeminal branches. QST abnormalities were found in the symptomatic division and in the other two branches on the same side. Minor contralateral changes were also found. Differences consisted of cold and warm hypoaesthesia and higher cold and heat pain thresholds in patients. All differences proved statistically significant. Our findings suggest that trigeminal neuralgia is not only a paroxysmal single nerve disorder, but also that other higher structures may be involved.

Repeated noxious stimulation of the skin enhances cutaneous pain perception of migraine patients in-between attacks: clinical evidence for continuous sub-threshold increase in membrane excitability of central trigeminovascular neurons

Recent clinical studies showed that acute migraine attacks are accompanied by increased periorbital and bodily skin sensitivity to touch, heat and cold. Parallel pre-clinical studies showed that the underlying mechanism is sensitization of primary nociceptors and central trigeminovascular neurons. The present study investigates the sensory state of neuronal pathways that mediate skin pain sensation in migraine patients in between attacks. The assessments of sensory perception included (a) mechanical and thermal pain thresholds of the periorbital area, electrical pain threshold of forearm skin, (b) pain scores to phasic supra-threshold stimuli in the same modalities and areas as above, and (c) temporal summation of pain induced by applying noxious tonic heat pain and brief trains of noxious mechanical and electrical pulses to the above skin areas. Thirty-four pain-free migraine patients and 28 age- and gender-matched controls were studied. Patients did not differ from controls in their pain thresholds for heat (44+/-2.6 vs. 44.6+/-1.9 degrees C), and electrical (4.8+/-1.6 vs. 4.3+/-1.6 mA) stimulation, and in their pain scores for supra-threshold phasic stimuli for all modalities. They did, however, differ in their pain threshold for mechanical stimulation, just by one von Frey filament (P=0.01) and in their pain scores of the temporal summation tests. Increased summation of pain was found in migraineurs for repeated mechanical stimuli (delta visual analog scale (VAS) +2.32+/-0.73 in patients vs. +0.16+/-0.83 in controls, P=0.05) and repeated electrical stimuli (delta VAS +3.83+/-1.91 vs -3.79+/-2.31, P=0.01). Increased summation corresponded with more severe clinical parameters of migraine and tended to depend on interval since last migraine attack. The absence of clinically or overt laboratory expressed allodynia suggests that pain pathways are not sensitized in the pain-free migraine patients. Nevertheless, the increased temporal summation, and the slight decrease in mechanical pain thresholds, suggest that central nociceptive neurons do express activation-dependent plasticity. These findings may point to an important pathophysiological change in membrane properties of nociceptive neurons of migraine patients; a change that may hold a key to more effective prophylactic treatment.

Diabetic neuropathy: a review emphasizing diagnostic methods

Diabetic sensorimotor polyneuropathy (DSP) is the most common complication of diabetes. In order to manage DSP effectively, it is necessary to formulate an accurate diagnosis and monitor subjects regularly. This review of important aspects of the diagnosis of DSP starts with a conceptual framework that includes elements of DSP epidemiology, pathophysiology, and therapy. The emphasis of the review is to present our current understanding of diagnostic methods for DSP including their utility and limitations. Screening for DSP in the diabetes clinic can be achieved successfully using simple clinical tests. Clinical neurophysiological methods are necessary to exclude other diagnoses, stage severity, and monitor the course of DSP. Novel investigative techniques are highly promising, but their usefulness in the clinic setting remains limited at this time. This article presents an overview of diagnostic methods for DSP.

2003 Wolff Award: Possible parasympathetic contributions to peripheral and central sensitization during migraine

BACKGROUND

Neurologic signs of increased parasympathetic outflow to the head often accompany migraine attacks. Because increased parasympathetic outflow to the cranial cavity induces vasodilation of cerebral and meningeal blood vessels, it can enhance plasma protein extravasation and the release of proinflammatory mediators that activate perivascular nociceptors. We recently showed that activation of intracranial perivascular nociceptors induces peripheral and central sensitization along the trigeminovascular pathway and proposed that these sensitizations mediate the intracranial hypersensitivity and the cutaneous allodynia of migraine.

METHODS

The present study investigates possible parasympathetic contributions to the generation of peripheral and central sensitization during migraine by applying intranasal lidocaine to reduce cranial parasympathetic outflow through the sphenopalatine ganglion.

RESULTS

In the absence of migraine, patients were pain-free, and their skin sensitivity was normal. Their mean baseline pain thresholds were less than 15 degrees C for cold, more than 45 degrees C for heat, and more than 100 g for mechanical pressure. Their mean pain score was 7.5 of 10 (standard deviation, 1.4) during untreated migraine and 3.5 of 10 (standard deviation, 2.4) after the nasal lidocaine-induced sphenopalatine ganglion block (P <.0001). Most patients developed cutaneous allodynia during migraine, and their mean pain thresholds changed to more than 25 degrees C for cold, less than 40 degrees C for heat, and less than 10 g for mechanical pressure. Following the nasal lidocaine administration (sphenopalatine ganglion block), this allodynia remained unchanged in spite of the pain relief.

CONCLUSION

These findings suggest that cranial parasympathetic outflow contributes to migraine pain by activating or sensitizing (or both) intracranial nociceptors, and that these events induce parasympathetically independent allodynia by sensitizing the central nociceptive neurons in the spinal trigeminal nucleus.

Quantitative sensory testing cannot differentiate simulated sensory loss from sensory neuropathy

OBJECTIVE

To differentiate the quantitative sensory testing (QST) results of subjects simulating small and large fiber sensory loss from those of normal subjects and subjects with sensory peripheral neuropathy.

BACKGROUND

QST is used to measure sensory thresholds in clinical, epidemiologic, and research studies. It is not known whether there are objective test results that characterize the subject seeking to deceive the examiner.

METHODS

The Computer Aided Sensory Examination IV 4, 2, and 1 stepping algorithm was used to determine vibration and cold perception in nine naïve subjects. Subjects were asked to simulate sensory loss (on two occasions) and to respond normally on one occasion. Test results were compared to those of subjects with diabetic sensory neuropathy. Each QST trial was performed three times.

RESULTS

Reproducibility, measured by the intraclass correlation coefficient, was similar in all groups for the vibration perception test (simulation 1: 0.68 [95% CI 0.31, 0.91], simulation 2: 0.82 [95% CI 0.54, 0.95], normal response: 0.77 [95% CI 0.47, 0.94], and subjects with peripheral neuropathy: 0.76 [95% CI 0.18, 0.95]) and the cold perception test (simulation 1: 0.53 [95% CI 0.12, 0.85], simulation 2: 0.82 [95% CI 0.55, 0.95], normal subjects: 0.67 [95% CI 0.30, 0.90] and subjects with peripheral neuropathy: 0.88 [95% CI 0.57, 0.97]), all just noticeable difference units. There were no differences between performance characteristics in the two simulation trials. Responses to null stimuli did not differentiate between groups.

CONCLUSION

Test performance characteristics do not permit discrimination among subjects simulating sensory loss, subjects with normal responses, and subjects with peripheral neuropathy.

Quantitative thermosensory testing of the lingual and inferior alveolar nerves in health and after iatrogenic injury

Quantitative testing of the sensory thermal thresholds testing was applied at sites innervated by the third division of the trigeminal nerve in 20 patients with no reported sensory impairment and in 20 subjects with iatrogenic nerve injuries after third molar surgery. In the control group sensitivity to cooling was significantly greater than the sensitivity to warming at all sites. The labial mucosa innervated by the inferior alveolar nerve was significantly more sensitive to thermal changes than either the mental region or the lingual mucosa. At sites supplied by nerves that had been injured, there were raised thresholds to both warming and cooling compared with the control group, and with uninjured contralateral sites. The results indicate that this test can identify iatrogenic lingual and inferior alveolar nerve injury with reference to a control group but because of spatial variation selection of control sites for comparison should be done cautiously.

Botulinum toxin A and the cutaneous nociception in humans: a prospective, double-blind, placebo-controlled, randomized study

Aside from temporary chemodenervation of skeletal muscle and potential anti-inflammatory effects, a genuine peripheral antinociceptive effect of Botulinum Neurotoxin Type A (BoNT/A) has been suspected. To evaluate the effect of BoNT/A on cutaneous nociception in humans, 50 healthy volunteers received subcutaneous injections of 100 mouse units (MU) BoNT/A (Dysport) and placebo. Both forearms of each subject were treated in a double-blind fashion, one with verum, one with placebo. Heat and cold pain thresholds within the treated skin areas were measured with quantitative sensory testing (QST) and pain thresholds were evaluated with local electrical stimulation (ES). The tests were done before treatment, and after 4 and 8 weeks. No major side effects were noted. All participants completed the study. Heat and cold pain thresholds increased from baseline to week 4 by 1.4 degrees C for verum and by 1.1 degrees C for placebo. From baseline to week 8, the thresholds increased by 2.7 degrees C for verum and by 1.2 degrees C for placebo. Electrically induced pain thresholds shifted from baseline to week 4 by -0.07 mA for verum and by 0.01 mA for placebo. From baseline to week 8, the thresholds increased by 0.10 mA for verum and by 0.11 mA for placebo. None of these differences was statistically significant. The study shows that there is no direct peripheral antinociceptive effect of BoNT/A in humans. The efficacy of BoNT/A in various pain syndromes must be explained by other pathways such as chemodenervation or anti-inflammatory effects.

The neuropathy of erectile dysfunction

These studies were intended to explore the relationship between autonomic neuropathy and erectile dysfunction (ED). Sensory thresholds reflecting the integrity of both large diameter, myelinated neurons (ie pressure, touch, vibration) and small diameter axons (ie hot and cold thermal sensation) were determined on the penis and finger. Data were compared across subjects with and without ED, controlling for age, hypertension and diabetes. The correlation of specific thresholds scores and IIEF values were also examined. Seventy-three patients who visited the academic urology clinics at Montefiore hospital were evaluated. All patients were required to complete the erectile function domain of the International Index of Erectile Function (IIEF) questionnaire: 20 subjects had no complaints of ED and scored within the 'normal' range on the IIEF. Patients were subsequently tested on their index finger and glans penis for vibration (Biothesiometer), pressure (Semmes-Weinstein monofilaments), spatial perception (Tactile Circumferential Discriminator), and warm and cold thermal thresholds (Physitemp NTE-2). Sensation of the glans penis, as defined by the examined sensory thresholds, was significantly diminished in patients with ED and these differences remained significant when controlling for age, diabetes and hypertension. In contrast, thresholds on the index finger were equivalent in the ED and non-ED groups. Threshold and IIEF scores were highly correlated, consistent with an association between diminished sensation and decreasing IIEF score (worse erectile functioning). These relations also remained significant when controlling for age, diabetes and hypertension. The findings demonstrate dysfunction of large and small diameter nerve fibers in patients with ED of all etiologies. Further, the neurophysiologic measures validate the use of the IIEF as an index of ED, as objective findings of sensory neuropathy were highly correlated with worse IIEF scores. The sensory threshold methods utilized represent novel, non-invasive and relatively simple procedures, which can be used in a longitudinal fashion to assess a patient's neurological response to therapies.

An overview of neuropathic pain: syndromes, symptoms, signs, and several mechanisms

OBJECTIVE

An overview is presented of neuropathic pain syndromes, their characteristic symptoms and signs, and recent approaches to identifying their pathophysiologic mechanisms.

DESIGN

The results of recent clinical studies of neuropathic pain are reviewed. Chronic neuropathic pain syndromes are emphasized because these long-lasting and often disabling conditions present a much greater challenge for the clinician than acute pain. Peripheral neuropathic syndromes have received greater attention in the research literature than central pain, and studies of syndromes such as postherpetic neuralgia and painful diabetic neuropathy provide the basis for current knowledge of neuropathic pain.

CONCLUSIONS

Precise estimates of the prevalence of neuropathic pain are not available, but chronic neuropathic pain may be much more common than has generally been appreciated and its prevalence can be expected to increase in the future. There is considerable agreement that both peripheral and central processes contribute to many chronic neuropathic pain syndromes, and that these different mechanisms may explain the qualitatively different symptoms and signs that patients experience. The limitations of existing treatments for neuropathic pain and the inability to provide relief for many patients has stimulated ongoing studies that examine different approaches to preventing neuropathic pain.

Clinical and electrophysiologic correlates of quantitative sensory testing in patients with incomplete spinal cord injury

OBJECTIVE

To determine the degree of association among indices of preserved sensation derived from quantitative sensory testing (QST), somatosensory evoked potentials (SEPs), and the clinical characteristics of patients with spinal cord injury (SCI).

DESIGN

A controlled correlational study of diverse measures of preserved sensory function.

SETTING

Regional SCI rehabilitation center in Ontario, Canada.

PARTICIPANTS

Thirty-three patients with incomplete SCI and 14 able-bodied controls.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

QST measures of perceptual threshold for temperature and vibration, American Spinal Injury Association sensory scores (light touch, pinprick), and tibial nerve SEPs.

RESULTS

There was a low degree of association (kappa) between QST results and sensory scores (|kappa|=.05-.44). QST measures yielded greater numbers of patients with SCI being classified as impaired, suggesting a greater sensitivity of QST to detect more subtle sensory deficits. QST measures of vibration threshold generally corresponded to the patients' SEP recordings. QST measures of modalities conveyed within the same tract were significantly (P<.05) correlated (|r|=.46-.84) in patients with SCI, but not in controls, whereas those modalities mediated by different pathways had lower and generally nonsignificant correlations (|r|=.05-.44) in both patients and controls.

CONCLUSIONS

The low degree of association between QST measures and sensory scores is likely attributable to measurement limitations of both assessments, as well as various neuroanatomic and neuropathologic factors. QST provides more sensitive detection of preserved sensory function than does standard clinical examination in patients with incomplete SCI.

The late whiplash syndrome: a psychophysical study

Some patients who have sustained whiplash injuries present with chronic widespread pain and mechanical allodynia. This single-blind, case control matched study of 43 chronic whiplash patients sought to examine psychophysical responses to non-noxious stimuli and their relationship to psychological profiles. Symptom Check List 90-R (SCL-90-R), Neck Disability Index and Shortform McGill Questionnaire were completed prior to testing. Qualitative stimuli comprised light touch, punctate pressure, moderate heat and cold. Additionally, sustained vibration was administered using a vibrameter which allowed ramping of either frequency or amplitude. Twenty-eight patients reported vibration-induced pain. No control subject experienced pain in response to vibration. No significant differences in perception threshold to vibration were noted between patients and control group. Twenty-three patients and ten control subjects reported painful responses to cold. Eleven patients and nine control subjects experienced pain in response to moderate heat. Four patients rated punctate pressure and one patient rated light touch as painful. SCL-90-R profiles revealed an overall elevated level of distress in the whiplash group. No significant difference was found between patients with and without vibration-induced pain for any dimension of the SCL-90-R. Pain in response to non-noxious stimulation over presumably healthy tissues suggests that central mechanisms are responsible for ongoing pain in at least some whiplash patients. The additional findings of pain on punctate pressure and hyperalgesic responses to heat and cold stimuli are consistent with enhanced central responsiveness to nociceptor input. These results have important therapeutic and prognostic implications.

Small-fiber neuropathy

Small-fiber neuropathy is a common disorder. It is often "idiopathic" and typically presents with painful feet in patients over the age of 60. Autoimmune mechanisms are often suspected, but rarely identified. Known causes of small-fiber neuropathy include diabetes mellitus, amyloidosis, toxins, and inherited sensory and autonomic neuropathies. Occasionally, small-fiber neuropathy is diffuse or multifocal. Depending on the type of small-fiber neuropathy, autonomic dysfunction can be significant or subclinical. Diagnosis is made on the basis of the clinical features, normal nerve conduction studies, and abnormal specialized tests of small-fiber function. These specialized studies include assessment of epidermal nerve fiber density as well as sudomotor, quantitative sensory, and cardiovagal testing. The sensitivities of these tests range from 59-88%. Each has certain advantages and disadvantages, and the tests may be complementary. Unless an underlying disease is identified, treatment is usually directed toward alleviation of neuropathic pain.

Noise-enhanced vibrotactile sensitivity in older adults, patients with stroke, and patients with diabetic neuropathy

OBJECTIVE

To test the hypothesis that vibrotactile detection thresholds in older adults, patients with stroke, and patients with diabetic neuropathy can be significantly reduced with the introduction of mechanical noise.

DESIGN

A randomized controlled study.

SETTING

A university research laboratory.

PARTICIPANTS

Twelve healthy elderly subjects (age range, 67-85y), 5 patients with stroke (age range, 24-64y), and 8 patients with diabetic neuropathy (age range, 53-77y).

INTERVENTIONS

Each subject's detection thresholds (ie, minimum level of stimulus to be detected) for a vibrotactile stimulus without and with mechanical noise (ie, random vibration with a small intensity) were determined by using a 4-, 2-, and 1-stepping algorithm. The stimuli were applied to the fingertip and/or to the first metatarsal of the foot.

MAIN OUTCOME MEASURE

Detection threshold for a vibrotactile stimulus.

RESULTS

The detection threshold at the fingertip for the vibration stimulus with mechanical noise was significantly lower than that without mechanical noise for all 12 elderly subjects, for 4 of the 5 patients with stroke, and all 8 patients with diabetic neuropathy. For the 8 patients with diabetes, mechanical noise also significantly reduced the vibrotactile detection threshold at the foot.

CONCLUSIONS

Reduced vibrotactile sensitivity in older adults, patients with stroke, and patients with diabetic neuropathy can be significantly improved with input mechanical noise. Noise-based techniques and devices may prove useful in overcoming age- and disease-related losses in sensorimotor function.

Sensory neuropathy associated with metronidazole: report of four cases and review of the literature

OBJECTIVE

To better characterize sensory neuropathy associated with metronidazole.

METHODS

We report four patients who developed dysesthesias after metronidazole treatment. One received topical metronidazole only. All four underwent electrodiagnostic studies, including nerve conduction studies (NCS), quantitative sensory testing (QST), and quantitative sudomotor axon reflex testing (QSART). One underwent nerve biopsy.

RESULTS

NCS were normal in all patients. QST showed impaired vibration thresholds in three patients. Three of four patients had abnormal tests of small fiber function. Cooling thresholds were abnormal in one; QSART was abnormal in one and borderline in another. The nerve biopsy specimen showed mild loss of small myelinated axons.

CONCLUSIONS

This study shows that paresthesias associated with metronidazole exposure may be the result of a relatively mild sensory neuropathy with predominant involvement of small fibers and milder, mostly subclinical involvement of large fibers.

Small fibers involvement in Friedreich's ataxia

Although the involvement of large myelinated sensory fibers in Friedreich's ataxia (FA) is well documented, an impairment of unmyelinated fibers has not been described. We demonstrate an involvement of cutaneous unmyelinated sensory and autonomic nerve fibers in FA patients. We performed a morphological and functional study of cutaneous nerve fibers in 14 FA patients and in a population of control subjects. We used immunohistochemical techniques and confocal microscopy applied to punch skin biopsies from thigh, distal leg, and fingertip, and compared the density of epidermal nerve fibers (ENFs) with the results of mechanical pain sensation and thermal and tactile thresholds performed on hand dorsum, thigh, distal leg, and foot dorsum. We observed in our patients a statistically significant loss of ENFs, a reduced innervation of sweat glands, arrector pilorum muscles and arterioles, and an impairment of thermal and tactile thresholds and mechanical pain detection.

Quantitative assessment of neuropathic pain

Quantitative sensory testing (QST) refers to a group of protocols that allows for quantitative measures of somesthetic function. Several protocols evaluate perceptual threshold, whereas others evaluate perception of stimuli above threshold. Each protocol has its own advantages and disadvantages, but one must always weigh a trade-off between accuracy (with longer protocols) and expediency (with shorter protocols). In assessing patients with neuropathic pain, one is interested in both positive and negative sensory symptoms. QST studies, using either neuropathic pain patients or healthy volunteers who have been rendered temporarily hyperalgesic, have demonstrated that pain abnormalities can be modality specific. The fact that various pain abnormalities can exist independently of each other suggests that (at least partially) different neuropathologic processes are responsible for each one. Current research suggests that both peripheral sensitization and central sensitization play a role in these abnormal pain conditions, and identification of precise neuropathologic mechanisms is under active investigation.

Degeneration of nociceptive nerve terminals in human peripheral neuropathy

Patients with peripheral neuropathy have symptoms involving small-diameter nociceptive nerves and elevated thermal thresholds. Nociceptive nerves terminate in the epidermis of the skin and are readily demonstrated with the neuronal marker, protein gene product 9.5 (PGP 9.5). To investigate the pathological characteristics of elevated thermal thresholds, we performed PGP 9.5 immunocytochemistry on 3 mm punch skin biopsies (the forearm and the leg) from 55 normal subjects and 35 neuropathic patients. Skin innervation was evaluated by quantifying epidermal nerve densities. Epidermal nerve densities were reduced in neuropathic patients compared to normal subjects. Epidermal nerve densities were variably correlated with thermal thresholds. The proportion of neuropathic patients with reduced epidermal nerve densities was larger than the proportion of neuropathic patients with elevated thermal thresholds. These results indicated that degeneration of epidermal nerve terminals preceded the elevation of thermal thresholds. Skin biopsy together with immunocytochemical demonstration of epidermal innervation offers a new approach to evaluate small-fiber sensory neuropathy.

Relationship between penile thermal sensory threshold measurement and electrophysiologic tests to assess neurogenic impotence

OBJECTIVES

Erectile function is usually assessed by neurophysiologic tests such as the bulbocavernosus reflex or pudendal nerve somatosensory evoked potentials. These tests investigate only large nerve fibers, although erection depends on autonomic nerve fibers, which are of small diameter. Warm and cold sensory fibers have similar calibers as the autonomic nerve fibers, and their integrity can be reliably evaluated by the measurement of thermal sensory thresholds. We studied penile thermal sensory testing in parallel with standard electrophysiologic tests to assess their sensitivity in the diagnosis of penile neuropathy.

METHODS

Twenty-five normal male subjects without erectile dysfunction or evidence of diffuse neuropathy (group 1) and 35 diabetic patients who complained of impotence (group 2) were studied. Erectile function was quantitated using the erectile dysfunction symptom score. Warm, cold, and vibratory sensory thresholds were assessed on the dorsal aspect of the penis. In addition, penile sympathetic skin responses and pudendal nerve somatosensory evoked potentials were recorded.

RESULTS

We found a significant difference between the two groups in the erectile dysfunction symptom score (P <0.0001), cold threshold (P = 0.0007), and warm threshold (P = 0.0025), but not for the other parameters. The erectile dysfunction symptom score correlated with the penile warm and cold thresholds (P = 0.0006 and 0.002, respectively).

CONCLUSIONS

Thermal thresholds assess small nerve fiber damage, which can indirectly reflect autonomic disturbances, particularly in the context of a diffuse neuropathy such as diabetic polyneuropathy. Penile thermal sensory testing correlated strongly with the clinical evaluation of erectile function and is a new and promising tool for the diagnosis of neurogenic impotence.

Normative values for female genital sensation

OBJECTIVES

Neurologic disorders might be responsible for many cases of female sexual dysfunction. Yet, they are currently undiagnosed because of the lack of measurement tools to assess genital neural function. Therefore, our objective is to provide norms for sensory thresholds in the vagina and clitoris, for a wide range of patient ages.

METHODS

Vaginal and clitoral warm, cold, and vibratory sensory thresholds were measured in 89 healthy paid volunteers by the method of limits. Normograms were derived from this group of healthy volunteers. An additional 61 patients were also tested, for a total of 150 individuals. Sixty-two individuals (42 healthy volunteers and 20 patients) from the total group were tested twice to provide test-to-test repeatability data across the range of clinical (normal and abnormal) responses.

RESULTS

Normograms are presented, providing age-corrected upper and lower normal values, expressed as 95% confidence limits for warm, cold, and vibratory thresholds. Intertest repeatability is also reported.

CONCLUSIONS

Thermal and vibratory thresholds of both the vaginal and clitoral region are clinically feasible, valid, and repeatable. These can be applied as a valuable diagnostic tool to assess neural dysfunction through sensory assessment of the female genitalia.

Quantitative sensory studies in complex regional pain syndrome type 1/RSD

OBJECTIVE

Patients with complex regional pain syndrome type I (CRPSD1) may have thermal allodynia after application of a non-noxious thermal stimulus to the affected limb. We measured the warm, cold, heat-evoked pain threshold and the cold-evoked pain threshold in the affected area of 16 control patients and patients with complex regional pain syndrome type 1/RSD to test the hypothesis that allodynia results from an abnormality in sensory physiology.

SETTING

A contact thermode was used to apply a constant 1 degrees C/second increasing (warm and heat-evoked pain) or decreasing (cold and cold-evoked pain) thermal stimulus until the patient pressed the response button to show that a temperature change was felt by the patient. Student t test was used to compare thresholds in patients and control patients.

RESULTS

The cold-evoked pain threshold in patients with CRPSD1/RSD (p <0.001) was significantly decreased when compared with the thresholds in control patients (i.e., a smaller decrease in temperature was necessary to elicit cold-pain in patients with CRPSD1/RSD than in control patients). The heat-evoked pain threshold in patients with CRPS1/RSD was (p <0.05) decreased significantly when compared with thresholds in control patients. The warm- and cold-detection thresholds in patients with CRPS1/RSD were similar to the thresholds in control patients.

CONCLUSIONS

This study suggests that thermal allodynia in patients with CRPS1/RSD results from decreased cold-evoked and heat-evoked pain thresholds. The thermal pain thresholds are reset (decreased) so that non-noxious thermal stimuli are perceived to be pain (allodynia).

Anticonvulsants for neuropathic pain syndromes: mechanisms of action and place in therapy

Neuropathic pain, a form of chronic pain caused by injury to or disease of the peripheral or central nervous system, is a formidable therapeutic challenge to clinicians because it does not respond well to traditional pain therapies. Our knowledge about the pathogenesis of neuropathic pain has grown significantly over last 2 decades. Basic research with animal and human models of neuropathic pain has shown that a number of pathophysiological and biochemical changes take place in the nervous system as a result of an insult. This property of the nervous system to adapt morphologically and functionally to external stimuli is known as neuroplasticity and plays a crucial role in the onset and maintenance of pain symptoms. Many similarities between the pathophysiological phenomena observed in some epilepsy models and in neuropathic pain models justify the rational for use of anticonvulsant drugs in the symptomatic management of neuropathic pain disorders. Carbamazepine, the first anticonvulsant studied in clinical trials, probably alleviates pain by decreasing conductance in Na+ channels and inhibiting ectopic discharges. Results from clinical trials have been positive in the treatment of trigeminal neuralgia, painful diabetic neuropathy and postherpetic neuralgia. The availability of newer anticonvulsants tested in higher quality clinical trials has marked a new era in the treatment of neuropathic pain. Gabapentin has the most clearly demonstrated analgesic effect for the treatment of neuropathic pain, specifically for treatment of painful diabetic neuropathy and postherpetic neuralgia. Based on the positive results of these studies and its favourable adverse effect profile, gabapentin should be considered the first choice of therapy for neuropathic pain. Evidence for the efficacy of phenytoin as an antinociceptive agent is, at best, weak to modest. Lamotrigine has good potential to modulate and control neuropathic pain, as shown in 2 controlled clinical trials, although another randomised trial showed no effect. There is potential for phenobarbital, clonazepam, valproic acid, topiramate, pregabalin and tiagabine to have antihyperalgesic and antinociceptive activities based on result in animal models of neuropathic pain, but the efficacy of these drugs in the treatment of human neuropathic pain has not yet been fully determined in clinical trials. The role of anticonvulsant drugs in the treatment of neuropathic pain is evolving and has been clearly demonstrated with gabapentin and carbamazepine. Further advances in our understanding of the mechanisms underlying neuropathic pain syndromes and well-designed clinical trials should further the opportunities to establish the role of anticonvulsants in the treatment of neuropathic pain.

Thermal thresholds in complex regional pain syndrome type I: sensitivity and repeatability of the methods of limits and levels

OBJECTIVES

To study whether the method of levels (MLE) or the method of limits (MLI) is preferable as a method of measuring thermal perception thresholds in patients with complex regional pain syndrome type I (CRPS I).

METHODS

Perception thresholds for warmth and cold were measured twice, with both MLE and MLI, at a 1 month interval, both at unaffected and affected wrists (n=33) or feet (n=20) of patients with CRPS I of one extremity.

RESULTS

(1) Sensitivity for pathology was equal for both methods. (2) The agreement between thresholds measured by both methods was low at all locations, except for the unaffected wrist. Since thresholds measured with the MLI always contain reaction time artefacts, this lack of agreement favours the MLE. (3) At both unaffected and affected wrists, the MLE showed significantly better coefficients of repeatability as compared to the MLI for both sensations. However, at both unaffected and affected feet, there was no preference for either method as far as threshold measurement repeatability was concerned.

CONCLUSIONS

Abnormal thermal perception thresholds occurred in 20% (foot) to 36% (wrist) of the CRPS I patients on the affected side and in 15% (foot, wrist) on the unaffected side. The MLE is considered to be the preferable method to assess thermal perception thresholds in CRPS I.

The role of quantitative neurological examination in clinical neurotoxicology

The use of the clinical neurological examination to document abnormal signs in suspected neurotoxic disorders is described, recognizing that identifying an abnormal examination does not establish the cause of the problem. Several forms of quantitative tests of neurological function are discussed, and their application to the evaluation of neurotoxic disorders is reviewed. Although results of such testing are rarely specific for toxic exposure, these measures have important application in sequential evaluations to document small changes in neurologic function over time.

Quantitative sensory testing: effect of site and pressure on vibration thresholds

OBJECTIVE

To determine the effect of different sites and locally applied pressure on vibration thresholds.

METHODS

Vibration thresholds were compared in 47 normal volunteers at 3 sites of the index finger (pulp, dorsum of the middle phalanx and nail) and at two sites of the great toe (dorsum of the proximal phalanx and nail). The effect of local pressure (30, 50 and 100 g/1.22 cm(2)) were compared in 41 subjects at the dorsum of the middle phalanx of the index finger and the proximal phalanx of the great toe.

RESULTS

The hand was more sensitive than the foot for vibration. There were no significant differences in vibration thresholds at different sites of the index finger and different sites of the great toe. The pulp of the index finger yielded the least inter-individual variation. Testing under 30 and 50 g/1.22 cm(2) of pressure yielded equal vibration thresholds. Vibration threshold was higher when tested under 100 g/1.22 cm(2) at the index finger but not the great toe. This difference was small and clinically negligible.

CONCLUSION

Testing of vibration thresholds in normal subjects can be adequately conducted at several sites of the index finger and the great toe. The test can be adequately done under low pressure of 30-50 g/1.22 cm(2).

Neurophysiological studies of thin myelinated (A delta) and unmyelinated (C) fibers: application to peripheral neuropathies

Dysfunction of small fibers may appear in isolation or associated with large fiber lesions. In some acute neuropathies, such as pandysautonomia, small-fiber impairment is relatively pure but it may also appear in disorders with prominent somatic damage, such as Guillain-Barré syndrome, in which autonomic failure worsens the prognosis. At the present time, chronic idiopathic distal small-fiber neuropathy is diagnosed more frequently, and in some prevalent disorders, such as diabetic or amyloidotic polyneuropathies, small-fiber dysfunction is very noticeable. In pure autonomic failure, a peripheral autonomic failure exists, distinguishing it from multiple-system atrophy. Complex regional pain syndrome is a severe condition in which small fibers are responsible for disabling signs and symptoms, and only instrumental recordings lead to the proper treatment. Standard neurophysiological techniques evaluate large myelinated fibers exclusively. Small-fiber polyneuropathy has been considered as a type of somatic neuropathy, but thin myelinated and unmyelinated fibers are responsible not only for temperature and pain perception but also autonomic function. For instance, full autonomic evaluation is needed in some clinical situations such as autonomic failure in the elderly or orthostatic intolerance syndrome. To evaluate small-fiber impairment we need a battery of sensitive, reproducible, specific and noninvasive tests covering somatic and autonomic systems. In this review, we describe and analyze a number of neurophysiological techniques used to diagnose and characterize small-fiber dysfunction in humans. These include cardiovascular monitoring, sudomotor testing, pupillary responses and quantitative sensory tests, and also to some extent thermography and laser evoked potentials. The use of such techniques has proven useful not only for diagnosis, but also to guide adequate therapy and optimize follow-up.

Quantitative sensory testing: effect of site and skin temperature on thermal thresholds

OBJECTIVE

To determine the effect of different sites and local skin temperature on thermal thresholds.

METHODS

Cool and warm detection and cold and heat pain thresholds were compared in 46 normal volunteers at the thenar eminence (TE), dorsum of the hand (DH), volar surface of the wrist (VW) and dorsum of the foot (DF).

RESULTS

The hand is more sensitive than the foot for cool and warm. TE is more sensitive for warm than DH and VW but the difference is clinically negligible. DH and VW are equally sensitive to warm. TE, DH, and VW are equally sensitive to cool. Inter-individual variance is smallest at TE. Warm and cool thresholds are independent of local skin temperature (range of 27-37 degrees C). TE is less sensitive for cold pain but otherwise the hand and the foot are equally sensitive to thermal pain.

CONCLUSION

Testing of thermal thresholds in normal subjects can be adequately conducted at several sites at the hand, however, TE is preferred given the small inter-individual variability. TE may be preferred for evaluating hyperalgesia to cold given its higher threshold. Warming or cooling of the skin is unnecessary within the range normally encountered in routine clinical evaluation.

Quantitative sensory testing in patients with incomplete spinal cord injury

OBJECTIVE

To examine the utility of quantitative sensory testing (QST) to characterize sensory dysfunction in patients with spinal cord injury (SCI).

DESIGN

Perceptual thresholds to warm, cold, cold pain, and vibratory stimuli were investigated using a modified method of "limits."

METHOD

Three QST trials were administered to six lower leg dermatomes, on two different days, to estimate the reliability of measurement.

SETTING

Regional Spinal Cord Injury Rehabilitation Center in Ontario, Canada.

SUBJECTS

Twenty-one SCI patients with incomplete neurologic deficits and 14 able-bodied controls of similar age.

RESULTS

ANOVA revealed significantly (p < .05) reduced perceptual threshold values (hypoesthesia) for warm, cold, and vibratory sensation in the SCI group. There were no differences between group mean values for cold pain because of the inclusion of patients with hypoalgesia and hyperalgesia. Intraclass correlation coefficient estimates of reliability revealed large between-subject variability in the SCI patients associated with relatively small trial-to-trial variability within each day of testing, and appreciable between-day variances.

CONCLUSIONS

With QST in SCI there is a need for repeated measurements across days to establish stable baseline measures or outcomes following intervention. QST is a useful adjunct to clinical examination for assessment of preserved sensation.