Conduction block in carpal tunnel syndrome

Conduction blocks of the median nerve at the wrist in pregnancy and postpartum carpal tunnel syndromes

INTRODUCTION/AIMS

The aim in this study is to describe the clinical and electrophysiological patterns of pregnancy-related carpal tunnel syndrome (PRCTS) occurring during pregnancy or after delivery.

METHODS

Clinical, epidemiological, and electrodiagnostic (EDx) data were studied in 130 women with PRCTS onset during pregnancy (n = 80) or after delivery (n = 50). Twenty-six women with PRCTS underwent EDx analysis during pregnancy and 104 after delivery (83 within 6 months of delivery and 21 up to 24 months after pregnancy onset). PRCTS was compared with idiopathic CTS in a control group consisting of 57 age-matched women with 98 cases of CTS. Twenty-four women with PRCTS had clinical and electrophysiological follow-up after corticosteroid injection (CSI) at the wrist.

RESULTS

Clinical analysis showed a higher rate of bilateral and diurnal/permanent paraesthesia and more severe symptoms in PRCTS compared with idiopathic CTS. EDx analysis showed more severe abnormalities in classical tests and a higher rate of conduction block (CB) in PRCTS. Statistical analysis showed a strong negative correlation between the incidence and importance of CB and the time interval at which PRCTS women underwent EDx examination, between pregnancy onset and 24 months later. CSI resulted in significant clinical and EDx improvement in 22 of 24 PRCTS women, with disappearance of all motor and most sensory CBs.

DISCUSSION

The EDx pattern of PRCTS is an acute/subacute median nerve lesion at the wrist identified by many CBs. This occurs concurrently with hormonal changes, is responsible for more severe clinical symptoms and EDx data, and it explains why CSI is so effective.

Nerve excitability test and lead toxicity: a case-control study

BACKGROUND

Although conventional electrophysiological parameters have been proposed as clinical indicators for monitoring lead neuropathies, their correlations with blood lead level are weak. In this study, we investigated the applicability of nerve excitability tests (NETs) to evaluate lead intoxication.

METHODS

Fourteen workers who were exposed to lead with an elevated blood level ranging from 17.8 to 64.9 µg/dL and 20 healthy controls with similar ages and body heights were enrolled. Both workers and controls underwent nerve conduction studies (NCSs), motor evoked potentials (MEPs) with transcranial magnetic stimulation (TMS), and NETs.

RESULTS

NCSs showed prolonged distal latencies and decreased motor nerve conduction velocity of median nerves in the workers but without significant correlation to blood lead level (BLL). Significantly prolonged MEP latency was observed in the workers (+ 6 ms). NETs demonstrated hyperpolarized resting membrane potentials in stimulus-response curves and changes in the property of potassium channels under a hyperpolarized current in threshold electrotonus, implying that lead hyperpolarized nerves by interfering with potassium channels. NETs also showed a better correlation with BLL than conventional electrophysiological parameters.

CONCLUSIONS

Axonal hyperpolarization and central conduction delay are more apparently reflecting elevated BLL than NCS. NET may have the potential for early detection of lead neuropathy.

The sensitivity of median versus ulnar palmar mixed nerve study in the early diagnosis of carpal tunnel syndrome

Background

Electrodiagnostic tests (EDX) are the most frequent and applicable studies in early diagnosis of carpal tunnel syndrome (CTS), but the definitive sensitive and specific tests are still under study. We aimed to evaluate the role of the median versus ulnar palmar mixed nerve study (Mix M-U), and its sensitivity in comparison to other provocative comparison studies, in supporting the early diagnosis of CTS. This cross-sectional study included 142 idiopathic early CTS hands from 100 patients and 71 hands from 50 healthy subjects as a control group. We did routine median motor and sensory studies and 4 comparative tests namely median versus radial sensory study (MVR), Mix M-U, median versus ulnar sensory study (MVU), and median versus ulnar lumbrical-interossei motor study (LU-IN).

Results

The routine median motor and sensory latency and amplitude showed a statistically significant difference between CTS and control groups as (p< 0.05) and a highly statistically significant difference between the 2 groups as regards the 4 comparative tests as (p< 0.0001). The specificities of all the 4 comparative tests were higher than 90%. MVR test had the highest sensitivity (92.2%) and followed by Mix M-U study (82.2%) and MVU (78.7%), and the least sensitive test was the LM-IN (66.9%).

Conclusions

Although the patients’ results fall within the normal range according to the reference range in the literature, it showed a statistically significant difference when compared to controls. A high percentage of those symptomatic patients showed results of typical CTS when tested with the comparative studies so there is a need to use these sensitive tests to diagnose cases with early CTS. According to sensitivity studies, the selection of which tests to do in order is a challenging choice. For the diagnosis of cases with early CTS with a normal ordinary motor and sensory studies, MVR comparative technique appeared as the best sensitive and specific provocative electrophysiological test followed by the Mix M-U test. We recommend the use of a combination of both tests first in the diagnosis of early CTS and if one of them was negative we can use the other comparative studies MVU and then LM-IN studies.

[Entrapment neuropathies: a contemporary approach to pathophysiology, clinical assessment, and management : German version]

Entrapment neuropathies such as carpal tunnel syndrome, radiculopathies, or radicular pain are the most common peripheral neuropathies and also the most common cause for neuropathic pain. Despite their high prevalence, they often remain challenging to diagnose and manage in a clinical setting. Summarising the evidence from both preclinical and clinical studies, this review provides an update on the aetiology and pathophysiology of entrapment neuropathies. Potenzial mechanisms are put in perspective with clinical findings. The contemporary assessment is discussed and diagnostic pitfalls highlighted. The evidence for the noninvasive and surgical management of common entrapment neuropathies is summarised and future areas of research are identified.

Multifocal acquired demyelinating sensory and motor neuropathy misdiagnosed as carpal tunnel syndrome: a case report

Multifocal acquired demyelinating sensory and motor neuropathy (MADSAM), a subtype of chronic inflammatory demyelinating polyneuropathy, is a non-compressive peripheral nerve disorder. Symptoms of MADSAM include asymmetrical weakness and sensory deficits in the distribution of individual peripheral nerves, which are frequently noted in the distal portion of peripheral nerves. MADSAM can be easily misdiagnosed as any of the various compressive peripheral neuropathies. Here, we present a case of MADSAM misdiagnosed as carpal tunnel syndrome (CTS). A 53-year-old woman had bilateral asymmetrical hand weakness (left hand: significant weakness, right hand: slight motor weakness) and a slight weakness of her bilateral lower extremities. Sensory deficit was found on the volar side of her left hand. She had visited many clinics previously and was diagnosed with CTS. However, an electrodiagnostic study performed in our hospital did not identify CTS but indicated a demyelinating peripheral neuropathy in all limbs. On the basis of the patient’s clinical symptoms and laboratory findings, she was diagnosed with MADSAM. When patients exhibit progressive aggravating motor weakness and sensory deficits in more than one distal limb without a specific finding of compressive neuropathy in electrodiagnostic studies, clinicians should consider the possibility of MADSAM.

Is There a Role of Cupping Therapy in the Treatment of Carpal Tunnel Syndrome in Primary Care Setting?

Carpal tunnel syndrome (CTS) is a clinical syndrome, which causes significant morbidity. It is currently managed conservatively with splinting or steroidal injections. Where conservative management is unsatisfactory, surgical decompression is carried out. Because of dangerous complications of surgical procedures and increasing economical burden of CTS condition, safe, traditional, cost effective conservative adjunct option is being evaluated in this review article. Cupping therapy is an ancient but increasingly popular therapy for a variety of pathologies. Studies over the last decade have indicated potential therapeutic value of cupping therapy for the management of CTS. Whilst there is some biomedical rationale supporting the usage of cupping therapy in CTS the evidence is not sufficient to support the inclusion of cupping therapy in management of carpal tunnel syndrome in formal pathways. High quality trials with increased participant numbers, development of blinded study options and a regulatory body for cupping therapy are required so that cupping therapy can be established as a potent therapeutic option for CTS. The review was conducted to examine the efficacy of cupping therapy in management of CTS.

Electrophysiological investigation of motor axonal excitability in a mouse model of nerve constriction injury

Peripheral nerve injuries caused by focal constriction are characterised by local nerve ischaemia, axonal degeneration, demyelination, and neuroinflammation. The aim of this study was to understand temporal changes in the excitability properties of injured motor axons in a mouse model of nerve constriction injury (NCI). The excitability of motor axons following unilateral sciatic NCI was studied in male C57BL/6J mice distal to the site of injury at the acute (6 hours-1 week) and chronic (up to 20 weeks) phases of injury, using threshold tracking. Multiple measures of nerve excitability, including strength-duration properties, threshold electrotonus, current-threshold relationship, and recovery cycle were examined using the automated nerve excitability protocol (TRONDNF). Acutely, injured motor axons developed a pattern of excitability characteristic of ischemic depolarisation. In most cases, the sciatic nerve became transiently inexcitable. When a liminal compound muscle action potential could again be recorded, it had an increase in threshold and latency, compared to both pre-injury baseline and sham-injured groups. These axons showed a greater threshold change in response to hyperpolarising threshold electrotonus and a significant upward shift in the recovery cycle. Mathematical modelling suggested that the changes seen in chronically injured axons involve shortened internodes, reduced myelination, and exposed juxtaparanodal fast K⁺ conductances. The findings of this study demonstrate long-term changes in motor excitability following NCI (involving alterations in axonal properties and ion channel activity) and are important for understanding the mechanisms of neurapraxic injuries and traumatic mononeuropathies.

Early changes of nerve integrity in preclinical carriers of hereditary transthyretin Ala117Ser amyloidosis with polyneuropathy

BACKGROUND AND PURPOSE

Disease-modifying therapies provide new horizons for hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN) to slow neuropathic progression. Initiating treatment at the earliest time requires biomarkers reflecting both small- and large-fiber degeneration in carriers.

METHODS

This study included examinations of pathology (intraepidermal nerve fiber [IENF] density), physiology (nerve conduction studies, autonomic function test, and nerve excitability), and psychophysics (thermal thresholds) in carriers to compare to healthy controls and asymptomatic diabetic patients.

RESULTS

There were 43 carriers (44.2 ± 11.4 years, p.Ala117Ser in 42 carriers), 43 controls (43.4 ± 12.7 years) including 26 noncarrier families, and 50 asymptomatic diabetic patients (58.1 ± 9.5 years). Carriers had lower IENF densities than controls and similar densities as diabetic patients. Median nerve conduction parameters, especially distal motor latency, were the most frequent neurophysiological abnormality in carriers, could differentiate carriers from controls and diabetic patients, were correlated with IENF densities in carriers but not in controls and diabetic patients, and were correlated with nerve excitability parameters in carriers but not in controls. Fifteen carriers (34.9%) with electrophysiological evidence of median nerve entrapment at the wrist had lower IENF densities and more abnormal conduction parameters than carriers without. We defined nerve dysfunction index-the ratio of median distal motor latency to IENF density-which differentiated carriers from controls.

CONCLUSIONS

In late-onset ATTRv-PN carriers with predominant p.Ala117Ser, median conduction parameters were the most common neurophysiological abnormalities and served as surrogate signatures of small- and large-fiber impairment. Combination of median distal motor latency and IENF density can reflect early neuropathy in carriers.

Entrapment neuropathies: a contemporary approach to pathophysiology, clinical assessment, and management

Entrapment neuropathies such as carpal tunnel syndrome, radiculopathies, or radicular pain are the most common peripheral neuropathies and also the most common cause for neuropathic pain. Despite their high prevalence, they often remain challenging to diagnose and manage in a clinical setting. Summarising the evidence from both preclinical and clinical studies, this review provides an update on the aetiology and pathophysiology of entrapment neuropathies. Potential mechanisms are put in perspective with clinical findings. The contemporary assessment is discussed and diagnostic pitfalls highlighted. The evidence for the noninvasive and surgical management of common entrapment neuropathies is summarised and future areas of research are identified.

The optimum hand temperature to study nerve conduction in patients with carpal tunnel syndrome

To define the skin temperature at which diseased nerves are better differentiated from the healthy. Motor and sensory conduction of median and ulnar nerve were evaluated in 52 patients with carpal tunnel syndrome (CTS) and 52 matched healthy controls at environmental skin temperature (mean 32-33 °C), after warming by an average of 2 °C and cooling to approximately 6 °C below baseline. In the hot condition, group comparisons for the median nerve showed a similar rate of distal motor latency (DML) reduction and sensory conduction velocity (SCV) increase in CTS and controls. With cold, the rate of change was smaller for the patients: DML mean increase was 5% /°C (7% for controls) and SCV mean decrease was 2.5%/°C (3.2% for controls). Individual patients' analysis revealed fewer abnormal median DML and SCV values at hot or at cold, compared to environmental temperature. It is concluded that conduction adjustments for low hand temperatures based on healthy measurements resulted in overcorrection and therefore underdiagnosis of CTS. Alternatively, at excessive hand warming the convergence of patient and healthy measurements also lead to underdiagnosis. Maintenance of skin temperature at 32-33 °C, corresponding to normal body temperature, is the optimum approach and should always be employed in clinical practice.

Nerve conduction studies and EMG in carpal tunnel syndrome: Do they add value?

This paper summarises the views of four experts on the place of neurophysiological testing (EDX) in patients presenting with possible carpal tunnel syndrome, in guiding their treatment, and in reevaluations. This is not meant to be a position paper or a literature review, and heterogeneous viewpoints are presented. Nerve conduction studies should be performed in patients presenting with possible carpal tunnel syndrome to assist diagnosis, and may need to be repeated at intervals in those managed conservatively. There is evidence that local corticosteroid injection is safe and effective for many patients, thereby avoiding or deferring surgical decompression. All patients should undergo EDX studies before any invasive procedure for CTS (injection or surgery). Needle EMG studies are not obligatory, but may be needed in those with severe disease and those in whom an alternate or concomitant diagnosis is suspected.

Exploratory use of ultrasound to determine whether demyelination following carpal tunnel syndrome co-exists with axonal degeneration

Carpal tunnel syndrome (CTS) accompanied by secondary axonal degeneration cannot be clearly discriminated using the current cross-validated ultrasound severity classification system. This study aimed at exploring cut-off values of ultrasound parameters, including wrist cross-sectional area (W-CSA), wrist perimeter (W-P), ratio of cross-sectional area (R-CSA) and perimeter (R-P), changes of CSA and P from wrist to one third distal forearm (ΔCSA&ΔP) for differentiation. Seventy-three patients (13 male and 60 female) were assigned into group A (demyelination only, n = 40) and group B (demyelination with secondary axonal degeneration, n = 33) based on the outcomes of nerve conduction studies (NCS). Receiver Operative Characteristics (ROC) curves were plotted to obtain sensitivity, specificity, and accuracy of cut-off values for all the ultrasound parameters. The overall identified cut-off values (W-CSA 12.0 mm², W-P 16.27 mm, R-CSA 1.85, R-P 1.48, ΔCSA 6.98 mm², ΔP 5.77 mm) had good sensitivity (77.1–88.6%), fair specificity (40–62.2%) and fair-to-good accuracy (0.676–0.758). There were also significant differences in demographics (age and severity gradation, P < 0.001), NCS findings (wrist motor latency and conduction velocity, P < 0.0001; wrist motor amplitude, P < 0.05; distal sensory latency, P < 0.05; sensory amplitude, P < 0.001) and ultrasound measurements (W-CSA, W-P, R-CSA, R-P, ΔCSA&ΔP, P < 0.05) between groups. These findings suggest that ultrasound can be potentially used to differentiate demyelinating CTS with secondary axonal degeneration and provide better treatment guidance.

Local and Extensive Neuroplasticity in Carpal Tunnel Syndrome: A Resting-State fMRI Study

Carpal tunnel syndrome (CTS) is a most common peripheral nerve entrapment neuropathy characterized by sensorimotor deficits in median nerve innervated digits. Block-design task-related functional magnetic resonance imaging (fMRI) studies have been used to investigate CTS-related neuroplasticity in the primary somatosensory cortices. However, considering the persistence of digital paresthesia syndrome caused by median nerve entrapment, spontaneous neuronal activity might provide a better understanding of CTS-related neuroplasticity, which remains unexplored. The present study aimed to investigate both local and extensive spontaneous neuronal activities with resting-state fMRI. A total of 28 bilateral CTS patients and 24 normal controls were recruited, and metrics, including amplitude of low-frequency fluctuation (ALFF) and voxel-wise functional connectivity (FC), were used to explore synaptic activity at different spatial scales. Correlations with clinical measures were further investigated by linear regression. Decreased amplitudes of low-frequency fluctuation were observed in the bilateral primary sensory cortex (SI) and secondary sensory cortex (SII) in CTS patients (AlphaSim corrected P < .05). This was found to be negatively related to the sensory thresholds of corresponding median nerve innervated fingers. In the voxel-wise FC analysis, with predefined seed regions of interest in the bilateral SI and primary motor cortex, we observed decreased interhemispheric and increased intrahemispheric FC. Additionally, both interhemispheric and intrahemispheric FC were found to be significantly correlated with the mean ALFF.

Immune dysregulation in patients with carpal tunnel syndrome

Peripheral immunity plays a key role in maintaining homeostasis and conferring crucial neuroprotective effects on the injured nervous system, while at the same time may contribute to increased vulnerability to neuropathic pain. Little is known about the reciprocal relationship between entrapment neuropathy and peripheral immunity. This study investigated immune profile in patients with carpal tunnel syndrome (CTS), the most prevalent entrapment neuropathy. All patients exhibited neurophysiological abnormalities in the median nerve, with the majority reporting neuropathic pain symptoms. We found a significant increase in serum CCL5, CXCL8, CXCL10 and VEGF, and in CD4+ central and effector memory T cells in CTS patients, as compared to healthy controls. CCL5 and VEGF were identified as having the highest power to discriminate between patients and controls. Interestingly, and contrary to the prevailing view of CCL5 as a pro-nociceptive factor, the level of circulating CCL5 was inversely correlated with neuropathic pain intensity and median nerve motor latency. In contrast, the level of central memory T cells was positively associated with abnormal neurophysiological findings. These results suggest that entrapment neuropathy is associated with adaptive changes in the homeostasis of memory T cells and an increase in systemic inflammatory modulating cytokines/chemokines, which potentially regulate neuropathic symptoms.

Trimetazidine potentiates the antiepileptic activity and ameliorates the metabolic changes associated with pentylenetetrazole kindling in rats treated with valproic acid

Oxidative stress is implicated in epileptogenesis as well as in the metabolic changes associated with increased risk of atherosclerotic vascular disease in epilepsy. The present work investigated the impact of the antioxidant trimetazidine (TMZ) on the antiepileptic activity of valproic acid (VPA) and on the metabolic and histological changes in hippocampal, aortic, and hepatic tissues associated with epilepsy and (or) VPA. Rats were divided into non-pentylenetetrazole (non-PTZ) group subdivided into control and VPA-treated groups, and PTZ-treated group subdivided into PTZ, PTZ/VPA, PTZ/TMZ, and PTZ/VPA + TMZ groups. VPA treatment in PTZ rats resulted in an antioxidant effect with improvement in oxidative stress, metabolic and histopathological changes induced by PTZ in hippocampus, aortic, and hepatic tissues. TMZ exhibited anticonvulsant activity and potentiated the anticonvulsant effect of VPA. Combination of TMZ with VPA induced a greater reduction in oxidative stress, improvement in the metabolic and histopathological changes compared to VPA treatment. In contrast, VPA administration in non-PTZ-treated rats induced a pro-oxidative effect, associated with metabolic and histopathological changes in aortic and hepatic tissues. These findings suggest that co-administration of TMZ with VPA in epilepsy might antagonize not only the oxidative stress associated with epilepsy but might also counteract a potential pro-oxidative effect of VPA.

Double peak sensory nerve action potentials to single stimuli in nerve conduction studies

INTRODUCTION

In humans, sensory nerve action potentials (SNAPs) can show 2 separate deflections, i.e., double peak potentials (DPp), which necessarily means that 1 peak is delayed with respect to the other. DPps may have various origins and be due to either physical or physiological properties.

METHODS

We review the nature of commonly encountered DPps in clinical practice, provide the most likely interpretations for their physiological origin, and assess their reproducibility and clinical utility.

RESULTS

We classified the DPps into 3 categories: (1) simultaneous anodal and cathodal stimulation. (2) simultaneous recording from 2 different nerves at the same site, and (3) SNAP desynchronization.

CONCLUSIONS

Although the recording of DPps is not a standardized neurophysiological method, their study brings interesting cues about the physiology of nerve stimulation and paves the way for clinical application of such an observation. Muscle Nerve 55: 619-625, 2017.

Placebo-controlled investigation of low-level laser therapy to treat carpal tunnel syndrome

OBJECTIVE

This study investigated the short-term efficacy of low-level laser therapy (LLLT) in patients with mild to moderate carpal tunnel syndrome (CTS), lasting for <1 year.

METHODS

Seventy-nine patients with CTS were included in this double-blind, placebo-controlled study, and randomly divided in two treatment groups: Experimental group (EG), active laser group (40 patients); and control group (CG), placebo (sham) laser group (39 patients). A GaAlAs diode laser [780 nm, 30 mW continuous wave (CW), 0.785 cm(2), 38.2 mW/cm(2)] was applied in contact with four points perpendicularly to the skin over the carpal tunnel area for 90 sec per point (2.7 J, 3.4 J/cm(2)/point). Both groups were treated five times per week, once a day over 2 weeks, followed by 10 treatments every other day for 3 weeks, that is, for a total of 20 treatments. Clinical assessment, including visual analogue scale (VAS) pain rating, Tinel's sign, and median nerve conduction studies (NCSs) were evaluated before, and 3 weeks after, the last LLLT treatment.

RESULTS

Significant reduction in pain, reduction in the percentage of patients with a positive Tinel's sign, and shortening of sensory and motor latency time in the NCS examination was observed in the experimental LLLT group (but not in the control group).

CONCLUSIONS

This study has observed and documented the statistically significant short-term effects of LLLT on CTS patients in comparison with a placebo group. The results support this conclusion, especially if the LLLT is applied in the earlier stages of CTS, and with mild to moderate cases.

Sensory axons excitability changes in carpal tunnel syndrome after neural mobilization

Increased mechanosensitivity of the median nerve in carpal tunnel syndrome (CTS) has been demonstrated during upper limb tension test 1 (ULTT1) when the nerve is passively elongated. However, the neurophysiological changes of the sensory axons during stressing activities are unknown. The aim of present study was to verify possible changes in the excitability of median nerve afferent axons following nerve stress in elongation, in subjects with and without CTS. Eight CTS hands and eight controls were selected. Recruitment properties of the median nerve were studied by analyzing the relationship between the intensity of electrical stimulation and the size of motor response, before and after intermittent-repetitive neural mobilization. Only in CTS hands, after the intervention, the stimulus-response curve was strikingly abnormal: both plateau and slope values were significantly lower. During anatomical stress across the median nerve in elongation, compressive forces may exert mechanical traction on the median nerve, since it is 'tethered' at the carpal tunnel, resulting inactivation of Na(+) channels at the wrist, or impairment of energy-dependent processes which affect axonal conduction block. We conclude that in entrapment neuropathies, neural mobilization during nerve elongation may generate conduction failure in peripheral nerve. Our study supports specific considerations for patient education and therapeutic approaches.

Acupuncture Evoked Response in Contralateral Somatosensory Cortex Reflects Peripheral Nerve Pathology of Carpal Tunnel Syndrome

BACKGROUND

Most neuroimaging studies exploring brain response to different acupoints have been performed in healthy adults.

OBJECTIVE

The aim of this study was to compare brain responses to acupuncture at local versus distal acupoints in patients with carpal tunnel syndrome (CTS), who have chronic pain, versus healthy controls (HC) and correlate these responses with median nerve function.

MATERIALS AND METHODS

Brain response to electroacupuncture (EA; 2Hz) was evaluated with event-related functional MRI (fMRI) in patients with CTS (n=37) and age-matched HC (n=30). EA was applied at acupoints local (PC 7 to TW 5) and distal (SP 6 to LV 4) to the CTS lesions.

RESULTS

Brain response in both groups and acupoints included activation of the bilateral secondary somatosensory cortex (S2) and insula, and the contralesional primary somatosensory cortex (cS1). Deactivation was noted in ipsilesional primary somatosensory cortex (S1). A significant difference between local and distal acupoints was found in cS1 for HC, but not CTS. Furthermore, cS1 activation by EA at local acupoints was negatively correlated with median nerve peak sensory latency in HC, but was positively correlated in CTS. No correlation was found for EA at distal acupoints for either group.

CONCLUSIONS

Brain response to EA differs between CTS and HC and, for local acupoint stimulation, is associated with median nerve function, reflecting the peripheral nerve pathophysiology of CTS.

Acupuncture-evoked response in somatosensory and prefrontal cortices predicts immediate pain reduction in carpal tunnel syndrome

The linkage between brain response to acupuncture and subsequent analgesia remains poorly understood. Our aim was to evaluate this linkage in chronic pain patients with carpal tunnel syndrome (CTS). Brain response to electroacupuncture (EA) was evaluated with functional MRI. Subjects were randomized to 3 groups: (1) EA applied at local acupoints on the affected wrist (PC-7 to TW-5), (2) EA at distal acupoints (contralateral ankle, SP-6 to LV-4), and (3) sham EA at nonacupoint locations on the affected wrist. Symptom ratings were evaluated prior to and following the scan. Subjects in the local and distal groups reported reduced pain. Verum EA produced greater reduction of paresthesia compared to sham. Compared to sham EA, local EA produced greater activation in insula and S2 and greater deactivation in ipsilateral S1, while distal EA produced greater activation in S2 and deactivation in posterior cingulate cortex. Brain response to distal EA in prefrontal cortex (PFC) and brain response to verum EA in S1, SMA, and PFC were correlated with pain reduction following stimulation. Thus, while greater activation to verum acupuncture in these regions may predict subsequent analgesia, PFC activation may specifically mediate reduced pain when stimulating distal acupoints.

Altered brain morphometry in carpal tunnel syndrome is associated with median nerve pathology

Objective

Carpal tunnel syndrome (CTS) is a common median nerve entrapment neuropathy characterized by pain, paresthesias, diminished peripheral nerve conduction velocity (NCV) and maladaptive functional brain neuroplasticity. We evaluated structural reorganization in brain gray matter (GM) and white matter (WM) and whether such plasticity is linked to altered median nerve function in CTS.

Methods

We performed NCV testing, T1-weighted structural MRI, and diffusion tensor imaging (DTI) in 28 CTS and 28 age-matched healthy controls (HC). Voxel-based morphometry (VBM) contrasted regional GM volume for CTS versus HC. Significant clusters were correlated with clinical metrics and served as seeds to define associated WM tracts using DTI data and probabilistic tractography. Within these WM tracts, fractional anisotropy (FA), axial (AD) and radial (RD) diffusivity were evaluated for group differences and correlations with clinical metrics.

Results

For CTS subjects, GM volume was significantly reduced in contralesional S1 (hand-area), pulvinar and frontal pole. GM volume in contralesional S1 correlated with median NCV. NCV was also correlated with RD and was negatively correlated with FA within U-fiber cortico-cortical association tracts identified from the contralesional S1 VBM seed.

Conclusions

Our study identified clear morphometric changes in the CTS brain. This central morphometric change is likely secondary to peripheral nerve pathology and altered somatosensory afference. Enhanced axonal coherence and myelination within cortico-cortical tracts connecting primary somatosensory and motor areas may accompany peripheral nerve deafferentation. As structural plasticity was correlated with NCV and not symptomatology, the former may be a better determinant of appropriate clinical intervention for CTS, including surgery.

Technical considerations for measurement of median nerve conduction velocity at wrist

Nerve conduction velocity (NCV) testing for the median nerve is the gold standard for diagnosing carpal tunnel syndrome (CTS), which affects about 6% of the general population. However, NCV equipment is relatively expensive and not always available at outpatient clinics. This study investigated the effects of different sampling rates and electrode placements on the NCV values of the median nerve to establish the practical significance of those specifications. The NCV of the median nerve at the wrist was measured in 30 healthy subjects with sampling rates of 2 kHz or 10 kHz and wide or narrow spacing of the electrode; Paired t-tests were used to compare the NCV values acquired by the different testing protocols. We found that the sampling rate had a statistically significant effect on the NCV values (P < 0.01), while the electrode placements did not significantly affect the NCV values (P > 0.05). The findings of this study have implications for improving the cost-effectiveness and technical applicability of NCV instruments.

Clarifying distal axonal properties of the median nerve

INTRODUCTION

Although length-dependent axonal excitability changes have been reported in the median nerve, the mechanisms underlying these changes remain to be further clarified.

METHODS

Axonal excitability studies were performed on median nerve at the palm and wrist in 20 healthy controls, with responses recorded over the abductor pollicis brevis.

RESULTS

The strength-duration time constant was significantly shorter (palm: 0.35 ± 0.01 ms; wrist: 0.48 ± 0.03 ms; P < 0.001), whereas rheobase was significantly increased (palm: 2.90 ± 1.12 mA; wrist: 2.09 ± 1.11 mA; P < 0.05) at the palm. In addition, there was a significant increase in depolarizing threshold electrotonus at 90-100 ms (P < 0.001) and a reduction in S2 accommodation (P < 0.001) and late subexcitability (P < 0.001) at the palm. The changes in excitability were independent of factors influencing median nerve cross-sectional area.

CONCLUSIONS

The present study reveals significant length dependent changes in median nerve excitability which may reflect differences in intrinsic membrane properties.

Nerve compression, membrane excitability, and symptoms of carpal tunnel syndrome

INTRODUCTION

In this study we investigated the changes in axonal excitability and the generation of neurological symptoms in response to focal nerve compression (FNC) of the median nerve in carpal tunnel syndrome (CTS).

METHODS

Sensory excitability recordings were undertaken in 11 CTS patients with FNC being applied at the wrist using a custom-designed electrode.

RESULTS

During FNC, refractoriness increased significantly (62.4 ± 3.4%; P < 0.001), associated with a rapid reduction in superexcitability (16.9 ± 2.8%; P < 0.001) and sensory nerve action potential amplitude (SNAP) (32.4 ± 3.9%; P < 0.001), consistent with axonal depolarization. Associated with these changes, paresthesiae steadily increased throughout FNC, as did numbness. Reductions in SNAP amplitude and superexcitability developed more rapidly for CTS patients during FNC compared with controls, and these changes were associated with more marked symptoms.

CONCLUSIONS

Axonal responses to compression are impaired in CTS. This may suggest a greater reliance on axonal membrane Na(+) /K(+) -ATPase function.

Diurnal variation in clinical and electrophysiologic parameters associated with carpal tunnel syndrome

OBJECTIVE

Patients with carpal tunnel syndrome (CTS) often report aggravated symptoms in the early morning. In this study, we aimed to identify diurnal variations in clinical and electrophysiologic parameters of patients with CTS.

DESIGN

A cross-sectional clinical and electrophysiologic study was designed. First, electrophysiologic examinations were performed at 2 p.m. to confirm the diagnosis of patients who had been clinically labeled with CTS. Patients who were electrophysiologically and clinically diagnosed with CTS were included in the study, and electrophysiologic examinations were repeated at 7 p.m. and 7 a.m. A total of 64 hands with CTS (27 bilateral, 10 unilateral) and 40 control hands were studied. Grip and pinch strength of all the patients included in the study were measured using a hand dynamometer. Finally, a CTS clinical symptom severity scale and functional status scale were used to measure the symptoms and functional impairment, respectively.

RESULTS

The median motor nerve distal latency and median F-minimum latency were found to be prolonged in the CTS group in the morning, and the grip strength was also markedly reduced at this time. Similar results were obtained for the median palm mixed nerve conduction velocity and amplitude.

CONCLUSIONS

This study demonstrated that the clinical and electrophysiologic parameters of CTS patients were clearly different in the morning hours, with the symptoms of CTS manifesting at that time.

Changes in human sensory axonal excitability induced by focal nerve compression

The aim of the present study was to establish the changes in nerve excitability and symptom generation associated with the application of focal nerve compression (FNC). FNC was applied at the wrist by means of a custom-designed electrode in 10 healthy subjects, and was maintained for 24 min. Symptoms of paraesthesiae and signs of numbness were recorded every 30 s. Despite apparently minimal changes in axonal threshold, FNC was associated with prolongation in latency by 14.5 +/- 2.1% (P < 0.001) and reduction in compound sensory action potential (CSAP) amplitude by 34.3 +/- 5.1% (P < 0.001), with two subjects developing conduction block. The reduction in CSAP was associated with abolition of superexcitability, and an increase in refractoriness of 295.2 +/- 55.5% (P < 0.005) and strength-duration time constant (SDTC) by 48.1 +/- 10.3% (P < 0.005), all consistent with axonal depolarization. With release of FNC, threshold rapidly increased above pre-compression levels (P < 0.01), consistent with the development of axonal hyperpolarization. Associated with these changes in axonal excitability, paraesthesiae and numbness steadily increased throughout FNC and reached a peak at the termination of FNC, followed by a gradual recovery on release of FNC. When compared to previous studies that utilised the effects of more generalised limb ischaemia, the changes in axonal excitability recorded during FNC were qualitatively and quantitatively alike, suggesting that similar biophysical mechanisms contributed to the changes observed with both manoeuvres.

Ischaemic sensitivity of axons in carpal tunnel syndrome

Although carpal tunnel syndrome (CTS) is the most common human entrapment neuropathy characterized by paraesthesiae and numbness with nocturnal exacerbation, the mechanisms underlying the generation of these symptoms remain unclear. Consequently, the aim of the present study was to investigate the relationship between changes in axonal excitability and the development of neurological symptoms in response to an ischaemic insult in CTS patients. Sensory and motor excitability were measured in 10 CTS patients and compared with 10 healthy controls, with participants asked to report symptom generation and intensity during the development of limb ischaemia. To induce ischaemia, a sphygmomanometer was inflated above the elbow and maintained at 200 mmHg for 10 min. During ischaemia there were decreases in axonal threshold, with less overall reduction in CTS patients when compared with controls. Associated with these differences in threshold, both sensory (p < 0.001) and motor (p < 0.05) refractoriness increased dramatically in CTS patients. This prominent increase in refractoriness was accompanied by a significant reduction in compound sensory action potentials and compound motor action potentials amplitudes for CTS patients when compared with controls (p < 0.05). These changes in axonal excitability resulted in a higher intensity of numbness and paraesthesiae reported by CTS patients during ischaemia. The present study has established differences in the nerve excitability and symptom development during ischaemia for patients with mild and moderate CTS, and may suggest that axons in the median nerve of CTS patients have an altered functional capacity to respond to an ischaemic insult, further contributing to nocturnal exacerbation of their symptoms.

Assessing the accuracy of a combination of clinical tests for identifying carpal tunnel syndrome

The aim of the study was to investigate whether a combination of selected provocative manoeuvres and sensory testing could improve the accuracy of clinical diagnosis of carpal tunnel syndrome (CTS). Prospective studies were undertaken in 43 of 296 consecutive patients who were referred with suspected CTS and had undergone nerve conduction studies (NCS). Responses to Phalen's test, a modified carpal compression test (MCCT), and sensory testing over the thenar eminence were assessed for each patient. For each test (Phalen's; MCCT), sensitivity (0.64; 0.14), specificity (0.75; 0.96), positive likelihood ratio (PLR) (2.54; 3.64) and negative likelihood ratio (NLR) (0.49; 0.89) were calculated. The inclusion of sensory testing did not improve sensitivity (0.55; 0.13), specificity (0.75; 0.96), PLR (2.22; 3.29) or NLR (0.60; 0.91). These data indicate that assessment of thenar sensation does not improve the diagnostic accuracy of CTS. However, a positive Phalen's test is more likely to be associated with NCS changes that are consistent with CTS.

Evidence of altered motor axon properties of the ulnar nerve in carpal tunnel syndrome

OBJECTIVE

To analyse recruitment properties of ulnar nerve motor axons in 60 CTS patients with negative ulnar nerve electrodiagnostic tests.

METHODS

Recruitment properties of the ulnar nerve were studied by analysing the relationship between the intensity of electrical stimulation and the size of motor response, i.e. the stimulus-response curve. Parameters of the curve (threshold, slope and plateau) were compared with those of the corresponding curve of the median nerve and both with parameters of 30 control curves.

RESULTS

The ulnar nerve stimulus-response curve was strikingly abnormal and, except for severity, closely resembled that of the median nerve. The slope of the curve was significantly less than that of controls and decreased with increasing abnormalities of the median nerve. This suggested that the pathological process involving the ulnar nerve was contingent with the severity of median nerve involvement.

CONCLUSIONS

We propose that the ulnar nerve may be subject to compression in Guyon's canal as a consequence of high pressure in the carpal tunnel of CTS patients.

SIGNIFICANCE

Ectopic activity from ulnar axons may contribute to clinical spread of symptoms outside the median nerve territory in CTS. This does not exclude possible involvement of central plasticity mechanisms in producing extra-median symptoms in CTS patients.

Changes in the recruitment curve of the soleus H-reflex associated with chronic low back pain

OBJECTIVE

We investigated whether patients with chronic low back pain (CLBP) manifest changes in the excitability of the soleus H-reflex.

METHODS

H-reflex stimulus-response curve was studied in 14 CLBP patients and 14 age-matched healthy subjects. H-threshold, H-maximum size, H-steepness and H-latency were determined for both legs. Homosynaptic depression (HD), following a train of H-reflexes, and presynaptic inhibition (PI) from flexor afferents onto soleus Ia afferents were also evaluated.

RESULTS

H-threshold was significantly increased, H-size as a function of stimulus intensity was significantly different, and H-recruitment curve steepness was significantly lower in CLBP patients compared to healthy subjects. No significant difference in the amount of HD and PI of the H-reflex was found between the two groups. H-latency and Hmax/Mmax ratio was comparable between the subjects groups.

CONCLUSIONS

In CLBP there is a reduced excitability of group Ia afferent fibres from the soleus muscle to which presynaptic factors do not seem to contribute and that presumably depend on changes in the peripheral sensory input.

SIGNIFICANCE

Changes in H-reflex excitability may underlie a decrease in the gain of a peripheral sensor in CLBP. Estimation of soleus H-threshold and H-recruitment curve may contribute to the diagnostic evaluation of CLBP and may be used to monitor the efficacy of treatment.

Changes in motor axon recruitment in the median nerve in mild carpal tunnel syndrome

OBJECTIVE

To determine whether patients with mild carpal tunnel syndrome (CTS) and conventional electrodiagnostic evidence of selective involvement of sensory conduction show changes in motor axon recruitment in the median nerve.

METHODS

Wrist-to-abductor pollicis brevis (APB) motor axon conduction was studied by analysing the relationship between the intensity of electrical stimulation and the size of motor response (input-output curve) in 30 CTS patients with conventional electrodiagnostic evidence of selective involvement of sensory conduction. Parameters (threshold, slope and plateau) of input-output curves were compared with those obtained in 30 controls.

RESULTS

The slope of the input-output curve of CTS patients was less steep than that of controls. For stimulus intensity above M-wave threshold (MTh), fewer motor axons were recruited in patients than controls.

CONCLUSIONS

Motor fibres are affected in CTS when conventional electrodiagnostic tests show normal motor conduction. Altered recruitment of motor axons could mainly be due to impairment of energy-dependent processes which affect temporal dispersion of the compound volley or axonal conduction block.

SIGNIFICANCE

In mild CTS, motor fibres are more often affected than was originally thought. The sensitivity of wrist-to-APB motor conduction studies may be increased by using submaximal stimulus intensities.

Nerve excitability testing and its clinical application to neuromuscular diseases

Non-invasive nerve excitability testing measures the membrane polarization, ion channel function and paranodal/internodal condition of peripheral nerves. This technique has been recently used for various neuromuscular disorders, such as pure motor conduction block in multifocal motor neuropathy, conduction block in carpal tunnel syndrome and Na(+) channel function disorders in diabetic neuropathy, to shed light on their pathophysiology. Here, we review the basics of ion channel functions and membrane properties that influence nerve excitability, the basic principles of nerve excitability testing and the reported findings in various disorders.

Effect of foot and ankle position on tarsal tunnel compartment volume

BACKGROUND

Tarsal tunnel pressure is increased when the foot and ankle are positioned in eversion or inversion from neutral, aggravating symptoms of tarsal tunnel syndrome in some patients. Space-occupying lesions may cause tarsal tunnel syndrome. We hypothesized that positional change of the foot and ankle from neutral to eversion or inversion causes decreased tarsal tunnel compartment volume that may aggravate symptoms of posterior tibial nerve entrapment.

METHODS

MRI of 13 ankles in nine healthy subjects in three positions (neutral, eversion, inversion) were obtained with respect to the malleolar-calcaneal plane; this plane was defined by the distal tip of the anterior colliculus of the medial malleolus, the medial tubercle of the posterior calcaneal tuberosity, and the lateral tubercle of the posterior calcaneal tuberosity. The borders of the tarsal tunnel noted on the MRI were traced with a computer digitizing apparatus to determine the cross-sectional area of the tarsal tunnel on each image, and the slice thickness and interspace distance for the seven central images were used to calculate tarsal tunnel volume.

RESULTS

The mean tarsal tunnel volume was significantly greater when the foot and ankle were in neutral position (21.5 +/- 0.9 cm(3)) than in either full eversion (18.0 +/- 0.9 cm(3); p = or < 0.001) or inversion (20.3 +/- 1.0 cm(3); p = or < 0.001).

CONCLUSIONS

The results support the hypothesis that eversion and inversion of the foot and ankle cause decreased compartment volume of the tarsal tunnel and increased tarsal tunnel pressure that may contribute to symptoms of posterior tibial nerve entrapment in tarsal tunnel syndrome.

CLINICAL RELEVANCE

Neutral immobilization of the foot and ankle may relieve symptoms of posterior tibial nerve entrapment in tarsal tunnel syndrome by minimizing pressure on the nerve and maximizing tarsal tunnel compartment volume available for the nerve.