Cortical somatosensory evoked potentials: effects of positional changes

Supine and sitting lower extremity cortical somatosensory evoked potential (CSEP) examinations were performed in 30 healthy volunteers to establish normal values and to determine variations in SEP parameters caused by positional changes, side of stimulation, and the influence of height. CSEPs were recorded at Cz'-Fz (10-20 international EEG system) after stimulation of the saphenous, peroneal, and sural nerves at the ankle. Each nerve was tested in the supine and sitting positions. CSEP P1, N1 latencies and P1 - N1 amplitudes were recorded. The mean values of these parameters and side-to-side differences were determined for both positions. Parameter changes between the two positions were also determined. No statistically significant difference was found when comparing supine and sitting, or side-to-side values (p greater than 0.05). Regression analyses of P1 latency vs height revealed a significant positive correlation for both positions (p less than 0.0001-0.0045). Mean P1 and N1 latencies (msec) +/- 1SD, and mean P1 - N1 amplitudes (microV) +/- 1SD are as follows: peroneal nerve (n = 119) P1 = 39.5 +/- 2.98, N1 = 48.2 +/- 3.79, P1 - N1 = 1.41 +/- 0.81; sural nerve (n = 119) P1 = 41.3 +/- 4.03, N1 = 50.9 +/- 4.57, P1 - N1 = 1.31 +/- 0.61; saphenous nerve (n = 119) P1 = 41.5 +/- 4.02, N1 = 50.4 +/- 4.10, P1 - N1 = 0.87 +/- 0.30. The normative data generated by this study will help clinicians to distinguish normal variations in lower extremity CSEP parameters.(ABSTRACT TRUNCATED AT 250 WORDS)     

A Novel Method to Quantify Histochemical Changes Throughout the Mediolateral Axis of the Substantia Gelatinosa After Spared Nerve Injury: Characterization with TRPV1 and Substance P

Nerve injury dramatically increases or decreases protein expression in the spinal cord dorsal horn. Whether the spatial distribution of these changes is restricted to the central innervation territories of injured nerves or could spread to adjacent territories in the dorsal horn is not understood. To address this question, we developed a simple computer software-assisted method to precisely distinguish and efficiently quantify immunohistochemical staining patterns across the mediolateral axis of the dorsal horn 2 weeks after transection of either the tibial and common peroneal nerves (thus sparing the sural branch, spared nerve injury, [SNI]), the tibial nerve, or the common peroneal and sural nerves. Using thiamine monophosphatase (TMP) histochemistry, we determined that central terminals of the tibial, common peroneal, sural, and posterior cutaneous nerves occupy the medial 35%, medial-central 20%, central-lateral 20%, and lateral 25% of the substantia gelatinosa, respectively. We then used these calculations to show that SNI reduced the expression of SP and TRPV1 immunoreactivity within the tibial and peroneal innervation territories in the L4 dorsal horn, without changing expression in the uninjured, sural sector. We conclude that SNI-induced loss of SP and TRPV1 in central terminals of dorsal horn is restricted to injured fibers. Our new method enables direct comparison of injured and uninjured terminals in the dorsal horn so as to better understand their relative contributions to mechanisms of chronic pain.PerspectiveA simple computer software-assisted algorithm was developed to precisely distinguish and efficiently quantify immunohistochemical staining patterns across the mediolateral axis of the dorsal horn after distal sciatic-branch transection. This method will facilitate a better understanding of the relative contribution of injured and uninjured terminals to mechanisms of chronic pain.     

Overwork weakness in rats with acrylamide neuropathy

Exercised rats have larger myelinated nerve fibers than sedentary rats and exercised rats with acrylamide neuropathy have smaller fibers than acrylamide-treated sedentary rats. These nerve fiber changes were the result of work hypertrophy and overwork atrophy, respectively. This study was designed to reassess morphologic changes in nerves after overwork was induced in rats with acrylamide neuropathy and to test the effects of rest before and after an overwork period in rats with acrylamide neuropathy. The 4-week-old rats divided into four groups of eight rats. Acrylamide was administered to three groups (Groups 2, 3, and 4) to induce subacute paralysis followed by gradual ameriolation. Group 3 was exercised for the first 5 weeks and was rested for the last 5 weeks. Group 4 was exercised for the last 5 weeks. The diameter distribution of myelinated fibers of the tibial and sural nerves was analyzed. The percentage of larger myelinated fibers was decreased in all acrylamide-treated groups. The average values of fiber diameters in Group 4 were significantly smaller than injected sedentary animals (Group 2) or those with rest (Group 3), whereas no significant difference was found between the latter groups. Axonal degeneration of teased fibers was assessed in the tibial and sural nerves. The percentage of axonal degenerated fibers in exercised animals (Group 4) was significantly higher than in the other acrylamide-injected groups (Groups 2 and 3). This study supports the concept that acrylamide neuropathy worsens with moderate intensity of running activities for a prolonged period and that recovery may occur if vigorous exercise is avoided.     

Physical activity: its influence on nerve conduction velocity

In a group of 40 healthy subjects, distal and proximal latencies of the median, tibial, and peroneal motor, and sural sensory nerves and their respective skin surface temperatures (Tsk) were measured before and after walking or bicycling. The baseline tests were performed 30 minutes after resting in a constant room temperature of 24C. The ambulation or bicycling task was continued for 30 minutes at a constant rate. Postactivity tests were performed within 30 minutes and between 45 to 60 minutes after termination of activity. Another test was done 75 to 90 minutes after bicycle exercise. After walking, there was a significant increase in Tsk in all lower extremity nerves tested (p less than 0.01). The increases were accompanied by faster distal and proximal latencies in both testing periods (p less than 0.01). Median nerve Tsk, distal and proximal latencies did not differ significantly from baseline values initially, but 45 minutes after walking Tsk was elevated and proximal latency had become faster (p less than 0.01). Following bicycling, lower extremity Tsk was significantly reduced over tibial, peroneal, and sural nerves by the third testing period (p less than 0.01) but only sural latencies were significantly prolonged (p less than 0.05) by this time. In the upper extremities median Tsk was significantly elevated and distal latency had become significantly faster 45 minutes after bicycling. Our data suggest that activity significantly influences nerve conduction latency results due to tissue temperature alteration. In addition, 30 minutes of rest after activity may not be sufficient time for the lower extremity temperatures to become stable.     

Local analgesia by percutaneous electrical stimulation of sensory nerves

Experimental C-fiber pain caused by radiant heat was applied to the skin area supplied by the left sural nerve of 20 subjects. Percutaneous electrical stimulation (PNS) was performed on the left sural nerve, the left superficial peroneal nerve and the right superficial radial nerve. Stimulation frequencies were: 3, 50, 100, 300, 500 and 1000 Hz. The analgesia resulting at the different stimulation sites was recorded according to a preset scale of estimation. Without considering the influence of the different frequencies, the best analgesic effects were reached if noxious heating and PNS were both performed on the left sural nerve; the anatomical conditions prevented us from distinguishing between the effects of possible peripheral blockade or spinal modification of pain. PNS of the superficial peroneal nerve seems to indicate spinal, possibly polysegmental, interactions between C-fiber pain and electrical stimulation of thick myelinated fibers. However, long loop effects may also play a part in local analgesia as demonstrated by PNS of the right radial nerve.     

Quantification of intraoperative somatosensory evoked potential

Cortical (C) and spinal (S) somatosensory evoked potentials (SEP) were measured and quantified in 30 patients undergoing scoliosis surgery during the following periods: I, preincision; II, hypotension; III, instrumentation; IV, postinstrumentation; and V, skin closure. Paired two-tailed t tests were performed on all commonly measured SEP parameters comparing values obtained at periods I and II with each subsequent period. CSEP were obtained with Cz-Fz recording sites of the international 10-20 system while SSEP were obtained with recording electrodes at C7-Fz, following bilateral posterior tibial nerve stimulation at the ankles. From period I, CSEP P1 prolonged significantly across all periods but not from period II to subsequent periods. N1 remained stable from either period I or II until period V when latencies increased. P1-N1 amplitude decreased significantly between period I and other periods until period V when near base value was regained. Compared to period II however, P1-N1 amplitude did not differ significantly until period V when it increased beyond base. CSEP P2 and N2 latencies and amplitudes were less distinct and had high variability under our anesthetic technique which consisted of N2O-O2 and isoflurane 0.25%-0.50%, narcotics, nondepolarizing blocking agents, and induced hypotension. When attainable, they behaved in a similar pattern to the early CSEP. SSEP were obtained in 23 cases. The stability of latencies and amplitudes compared favorably with CSEP P1 and N1. Graphs of relative percent changes were developed for clinical use. It is concluded that the noninvasive monitoring technique described is practical, and that P1 and N1 CSEP and SSEP values are reliable monitoring parameters.     

Electrodiagnostic changes of the lower limbs in subjects with chronic complete cervical spinal cord injury

OBJECTIVE: To assess the electrodiagnostic changes in the lower limbs as measured by nerve conduction studies (NCSs) and electromyography in individuals with chronic complete tetraplegia. DESIGN: Prospective testing of NCS and electromyography. SETTING: Model spinal cord injury rehabilitation center. PARTICIPANTS: Twenty-five individuals with chronic complete tetraplegia without risk factors for peripheral neuropathy or other lower motoneuron disorders. INTERVENTIONS: Nerve conduction parameters recorded from the peroneal, tibial, and sural nerves, and compared with normal values. The presence of spontaneous activity (SA), including fibrillation and positive sharp waves, recorded in 5 muscle groups-2 proximal (vastus medialis, iliopsoas), 2 distal (tibialis anterior, medial gastrocnemius), and L4 lumbar paraspinals. Analysis to see if the presence of SA correlated with the distance of the muscle from the spinal cord or with spasticity (measured by the modified Ashworth scale). MAIN OUTCOME MEASURES: Nerve conduction latencies and velocities; motor and sensory conduction latencies; compound muscle action potential (CMAP) and sensory nerve action potential amplitudes; spontaneous potentials: fibrillation and positive sharp waves; and spasticity. RESULTS: NCS responses were obtained at a decreased frequency relative to able-bodied subjects. Statistically significant results in comparison to normal means included a diminished sural amplitude, and diminished peroneal and tibial CMAP and nerve conduction velocity (p <.0001). SA was recorded in at least 1 of the muscles tested in 92% of subjects, with 72% having SA in more than 1 of the muscles tested affected. A significant difference was seen for SA in the medial gastrocnemius as compared with the iliopsoas (p =.039). No correlation was noted in terms of SA with degree of spasticity. CONCLUSION: A statistically significant difference in NCS responses in the lower limbs in chronic tetraplegia was found relative to normal control values. However, only the frequency of responses elicited and the decreased CMAP of the peroneal nerve are clinically significant. SA was present in many of the lower extremity muscles in the subjects. Predominantly axonal changes were evident in individuals with chronic complete tetraplegia.     

大鼠慢性渐进性脊髓损伤减压后脊髓诱发电位的变化

目的研究对大鼠慢性渐进性脊髓损伤减压后诱发电位的变化,探讨减压后神经功能恢复的规律。方法将动物随机分为正常组,慢性渐进性脊髓损伤组,慢性渐进性脊髓损伤组+减压后1、2、3、5、7、10、14、20、28d组,分别观察其皮层体感诱发电位(CSEP)和运动诱发电位(MEP)的变化,用Tarlov评分及斜板试验来评价神经功能。结果慢性渐进性脊髓损伤减压后CSEP和MEP潜伏期明显缩短,波幅明显升高,其中前7d变化较快,7d后CSEP和MEP潜伏期分别缩短了39%、34%,波幅分别增加了62%、48%,以后变化不明显,脊髓的神经功能于前10d恢复较快,以后有升高但变化不明显。结论慢性渐进性脊髓损伤减压后脊髓神经功能于减压早期即10d左右有一迅速的恢复,以后变化不明显。     

H-reflex latency in uremic neuropathy: correlation with NCV and clinical findings.

Sixty-two uremic patients on dialysis of varying durations were tested bilaterally for posterior tibial nerve H-reflex latency, at 3-month intervals. Bilateral nerve conduction velocities (NCVs) of the peroneal, tibial, and sural nerves were concomitantly determined in all subjects. Proprioception sense, vibration perception threshold at the great toes, and deep tendon reflexes at the knee and ankle were determined in all subjects on the day of electrodiagnostic testing. The sensitivity of the H-reflex latency in detection of the onset and severity of uremic neuropathy was assessed. H-reflex latency changes were compared to NCV and clinical test results. The following was found: (1) of the parameters studied, the H-reflex latency appeared to be the most sensitive indicator of early uremic polyneuropathies, (2) electrodiagnostic tests were more sensitive to the onset of neuropathies than the clinical testing parameters studied, and (3) the sural sensory nerve appeared to be involved earlier than peroneal and tibial motor nerves in neuropathies studied.     

Race effect on nerve conduction studies: a comparison between 50 blacks and 50 whites.

OBJECTIVE: To determine whether there are any differences in nerve conduction study results between blacks and whites. DESIGN: The following studies were performed: median, ulnar, peroneal, and tibial motor studies; median and ulnar mixed motor/sensory studies; sural and radial sensory studies; and H-reflex studies. SETTING: Private office or university-based clinic. PARTICIPANTS: Fifty adult blacks and 50 adult whites who met inclusion criteria, recruited through advertisements. MAIN OUTCOME MEASURES: Differences between blacks and whites were compared to determine whether they exceeded a cutoff of 0.2 msec for latencies, 20% difference for amplitudes, 5 m/sec for conduction velocity, and 1.2 msec for H-reflex times. A repeated analysis of variance was performed to detect statistically significant differences (defined as p< or =.01). RESULTS: Only values for the mean peroneal and tibial motor latencies exceeded the cutoff times. The mean peroneal response was faster by 0.3 msec and the mean tibial response was slower by 0.3 msec in blacks than whites. These differences were not statistically significant at a level of p< or =.01. CONCLUSION: There is no significant difference between blacks and whites in normal nerve conduction study findings in healthy adults.     

尿毒症患者周围神经的电生理研究

目的研究尿毒症患者周围神经的电生理表现。方法选择尿毒症患者24 例及同期健康对照者19 例,采用常规表面电极对胫后神经、腓总神经、腓肠神经及皮肤交感反应进行检查,观察尿毒症患者周围神经的电生理表现。结果两组运动传导、感觉传导及交感皮肤反应潜伏期均有显著性差异(P<0.05)。电生理表现主要为F 波的潜伏期延长,传导速度减慢,潜伏期延长,感觉纤维受累重于运动纤维。结论尿毒症性周围神经病是尿毒症最常见的并发症之一,神经电生理的异常明显早于临床症状,周围神经的电生理检查对该病的诊断及评价具有重要意义。     

不同频率毫米波治疗脊髓损伤的实验研究

目的 :研究毫米波对损伤脊髓修复的生物效应。方法 :采用波长为4.9mm、7.1mm、8.9mm,输出功率密度7mW/cm2 的毫米波治疗大鼠损伤脊髓 ,30min,2次/d×20,观察组织学及CSEP、MEP变化。结果 :7.1mm -7mW/cm2治疗组与损伤组比较脊髓组织病变轻 ,CSEP潜伏期缩短。结论 :毫米波能促进损伤脊髓的修复     

Sural nerve conduction studies and late responses in children undergoing hemodialysis

Physiologic evidence of peripheral neuropathy has been described previously in children undergoing hemodialysis. In order to detect early or subclinical evidence of peripheral neuropathy, several newer electrophysiologic techniques, including latencies of late responses (H reflex and F response) and sural nerve sensory studies, were evaluated in addition to routine motor and sensory conduction in 17 randomly selected children (mean age 14.2 years) undergoing hemodialysis (12 of whom had no clinical evidence of peripheral neuropathy) and 20 age-matched normal control subjects. Conventional motor and sensory conduction studies of median and ulnar nerves and motor conduction of peroneal and tibial nerves showed abnormalities of motor conduction in 5 (29%) and abnormalities of sensory conduction in 2 (12%). Sural nerve sensory potentials were abnormal in 10 (59%) patients. Late response were significantly abnormal in 10 (59%) patients, 5 (29%) of whom had normal routine motor conduction studies in the same nerve distribution. The abnormalities of late responses and motor and sensory conduction were more evident in lower limbs. Studies of late responses and sural sensory conduction provide a method of detecting subclinical neuropathy in this patient population at a time when results of conventional motor and sensory conduction tests are within normal limits. Effects of dialysis may then be followed quantitatively in patients whose neuropathy would otherwise be undetectable.     

Spared nerve injury: an animal model of persistent peripheral neuropathic pain

Peripheral neuropathic pain is produced by multiple etiological factors that initiate a number of diverse mechanisms operating at different sites and at different times and expressed both within, and across different disease states. Unraveling the mechanisms involved requires laboratory animal models that replicate as far as possible, the different pathophysiological changes present in patients. It is unlikely that a single animal model will include the full range of neuropathic pain mechanisms. A feature of several animal models of peripheral neuropathic pain is partial denervation. In the most frequently used models a mixture of intact and injured fibers is created by loose ligation of either the whole (Bennett GJ, Xie YK. A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man. Pain 1988;33:87-107) or a tight ligation of a part (Seltzer Z, Dubner R, Shir Y. A novel behavioral model of neuropathic pain disorders produced in rats by partial sciatic nerve injury. Pain 1990;43:205-218) of a large peripheral nerve, or a tight ligation of an entire spinal segmental nerve (Kim SH, Chung JM. An experimental model for peripheral neuropathy produced by segmental spinal nerve ligation in the rat. Pain 1992;50:355-363). We have developed a variant of partial denervation, the spared nerve injury model. This involves a lesion of two of the three terminal branches of the sciatic nerve (tibial and common peroneal nerves) leaving the remaining sural nerve intact. The spared nerve injury model differs from the Chung spinal segmental nerve, the Bennett chronic constriction injury and the Seltzer partial sciatic nerve injury models in that the co-mingling of distal intact axons with degenerating axons is restricted, and it permits behavioral testing of the non-injured skin territories adjacent to the denervated areas. The spared nerve injury model results in early (<24 h), prolonged (>6 months), robust (all animals are responders) behavioral modifications. The mechanical (von Frey and pinprick) sensitivity and thermal (hot and cold) responsiveness is increased in the ipsilateral sural and to a lesser extent saphenous territories, without any change in heat thermal thresholds. Crush injury of the tibial and common peroneal nerves produce similar early changes, which return, however to baseline at 7-9 weeks. The spared nerve injury model may provide, therefore, an additional resource for unraveling the mechanisms responsible for the production of neuropathic pain.     

肯定型肌萎缩性侧索硬化症的运动神经传导速度和F波改变特点及其影响因素

目的 观察肯定型肌萎缩性侧索硬化症(definite amyotrophic lateral sclerosis，DALS)的运动神经传导速度(motor neuron conduction velocity，MCV)和F波改变特点，以及病情和病程对MCV和F波的影响。方法 对46例肯定型ALS患者和正常对照组的：MCV和F波进行测定。结果 患者组正中神经、尺神经、胫神经和腓深神经的末端运动潜伏期(distal motor latency，DML)明显延长。F波的出现率、近端段／中枢潜伏期和左右往返脊髓的近端段／中枢潜伏期的差值与对照组比较差异均有显著性意义。患者重度组4条神经的DML显著延长，MCV明显减慢和波幅明显降低，重度组正中神经和尺神经的DML、MCV和波幅与轻度组比较差异也有显著性意义。随访患者组3年，其运动神经传导速度和F波检查结果经配对方差检验，差异均有显著性意义。结论 MCV和F波可作为ALS电生理诊断的一项有价值的检查,其异常程度与病情和病程有关。     

肌萎缩侧索硬化症的周围神经损害

目的 阐明肌萎缩侧索硬化症患者腓肠神经的病理改变特点。方法 选择已确诊的肌萎缩侧索硬化症患者行周围神经活检。取其腓肠神经进行光镜及电镜检查，观察其病理改变。结果 周围神经的改变以轴索损害为主，伴有髓鞘的脱失。根据病理改变可分为4组：正常；轻度轴索变性及髓鞘脱失；有髓神经纤维轻度脱失，轴索变性及脱髓鞘；有髓神经纤维严重脱失，轴索变性及脱髓鞘。结论 肌萎缩侧索硬化症患者常常早期即出现周围神经的损害，其中以轴索性的改变为主，同时可伴有不同程度的髓鞘脱失。     

Assessment and analysis of mechanical allodynia-like behavior induced by spared nerve injury (SNI) in the mouse

Experimental models of peripheral nerve injury have been developed to study mechanisms of neuropathic pain. In the spared nerve injury (SNI) model in rats, the common peroneal and tibial nerves are injured, producing consistent and reproducible pain hypersensitivity in the territory of the spared sural nerve. In this study, we investigated whether SNI in mice is also a valid model system for neuropathic pain. SNI results in a significant decrease in withdrawal threshold in SNI-operated mice. The effect is very consistent between animals and persists for the four weeks of the study. We also determined the relative frequency of paw withdrawal for each of a series of 11 von Frey hairs. Analysis of response frequency using a mixed-effects model that integrates all variables (nerve injury, paw, gender, and time) shows a very stable effect of SNI over time and also reveals subtle divergences between variables, including gender-based differences in mechanical sensitivity. We tested two variants of the SNI model and found that injuring the tibial nerve alone induces mechanical hypersensitivity, while injuring the common peroneal and sural nerves together does not induce any significant increase in mechanical sensitivity in the territory of the spared tibial nerve. SNI induces a mechanical allodynia-like response in mice and we believe that our improved method of assessment and data analysis will reveal additional internal and external variability factors in models of persistent pain. Use of this model in genetically altered mice should be very effective for determining the mechanisms involved in neuropathic pain.     

皮层体感诱发电位监测脊髓牵张性损害的实验研究

目的　探讨术中及术后皮层体感诱发电位 (CSEP)对脊髓牵张性损害的监测作用。方法　切除大鼠T13 ～L2 双侧椎板显露脊髓 ,用特制的脊柱撑开器放置在大鼠T12 ～L3 椎体横突上纵向牵张 ,同时用CSEP进行术中、术后监测。 40只SD大鼠随机分成对照组和CSEPP1 N1波幅下降 3 0 % ,5 0 % ,70 %组 ,观察术中、术后CSEP的变化 ,比较各组术后神经功能和病理检查结果。结果　随着撑开距离的增加 ,波幅下降至术前波幅 3 0 %组及正常组的CBS评分分别为 (14 .80± 3 .98)和 0分 ,神经元计数分别为 (79.60± 3 .5 3 )个和 (82 .70± 3 .41)个 ,二者相比差异无显著性意义。光镜下脊髓神经元体积稍小 ,神经纤维形态正常 ;波幅下降 5 0 %及 70 %组的CBS评分分别为 (5 2 .10± 6.12 )和 (74.60± 8.97)分 ,神经元计数分别为 (67.80± 3 .85 )个和 (4 5 .70± 4.42 )个。与正常组及 3 0 %组相比差异有显著性意义 (P <0 .0 1)。光镜观察神经元间隙增大 ,神经元退变、减少、溶解或坏死 ,脊髓结构破坏 ,出现片状出血灶 ,大量胶质细胞浸润。结论　CSEP对脊髓牵张性损害具有良好的监测作用 ,对脊髓神经功能和预后判断具有重要价值     

Spinal nerve ligation-induced neuropathy in the rat: sensory disorders and correlation between histology of the peripheral nerves

We studied the effect of unilateral ligation of two spinal nerves on behavioral pain responses evoked by various types of cutaneous stimuli in the adult rat. Furthermore, we determined the effect of spinal nerve ligation on morphology of the peripheral nerves. The most consistent behavioral finding (83%) was a marked decrease in monofilament-induced hindlimb withdrawal thresholds (mechanical allodynia) ipsilateral to the spinal nerve ligation. This mechanical allodynia was observed as early as during the 1st post-operative day and it persisted up to 2 months (the maximum length of the observation period). In contrast, hyperalgesia to noxious mechanical stimulation (Randal-Sellitto test) was not observed in allodynic rats until the 3rd post-operative day. In a minority of rats (13%), spinal nerve ligation-induced mechanical hyperalgesia without a concomitant mechanical allodynia. There was no corresponding heat hyperalgesia in the injured hindlimb (hot water immersion-, radiant heat- or hot-plate-induced hindlimb withdrawal tests). In contrast, hypoalgesia to heat was observed on the 1st postoperative day, but not later. Neuropathological analysis of the peripheral nerves revealed a dramatic decrease in the number of myelinated nerve fibers distal to the spinal nerve ligation site. The results support the previous evidence indicating that ligation of spinal nerves induces a marked allodynia to mechanical stimulation. However, this mechanical allodynia may differentially dissociate from mechanical and thermal hyperalgesia at various post-operative time points. The marked mechanical allodynia together with a dramatic decrease in the number of myelinated nerve fibers is paradoxical, since the activation of myelinated nerve fibers by monofilaments produced abnormally strong behavioral responses. This paradox may be explained by spinal nerve ligation-induced amplification or disinhibition of tactile signals at central levels.     

Peripheral Nerve Ultrasound in Small Fiber Polyneuropathy

Routine nerve conduction studies are normal in patients with small fiber neuropathy (SFN), and a definitive diagnosis is based on skin biopsy revealing reduced intra-epidermal nerve fiber density (IENFD). In large fiber polyneuropathy, ultrasound (US) parameters indicate enlargement in cross-sectional area (CSA). This study was aimed at determining if similar changes in large fibers on US are apparent in patients with SFN. Twenty-five patients with SFN diagnosed by reduced IENFD and 25 age- and body mass index (BMI)-matched healthy controls underwent US studies of sural and superficial peroneal sensory nerves. The mean CSA of the sural nerve in SFN patients was 3.2 ± 0.8 mm², and in controls, 2.7 ± 0.6 mm² (p < 0.0070), and this was independent of sex. There was no difference in the thickness-to-width ratio or echogenicity of the nerves. US of the sural nerve in patients diagnosed with small fiber neuropathy reveals an enlarged cross-sectional area similar to that in large fiber polyneuropathy.