Sensory Action Potentials Research Articles

ELECTROPHYSIOLOGICAL ABNORMALITIES IN DIABETIC PATIENTS

We studied 476 patients affected by diabetes: 166 male (mean age 61.6 ± 10 years, range 27–91) and 310 female (mean age 61.5 ± 8.4 years, range 25–82). Mean disease duration was 11.3 ± 7.6 years, range 0.3–37).All patients underwent surface motor and sensory nerve conduction along median, popliteal, and sural nerve.Results. Median nerve: in 3.1% of subjects sensory action potentials (SAP) was absent; sensory nerve conduction velocity (SNCV) was reduced in 41.8% in distal segment and in 27.5% in the proximal segment. Motor nerve conduction (MNCV) was reduced in 29.9% of the subjects.Sural nerve: SAP was absent in 24.4% and SNCV was reduced in 32.7%.Popliteal nerve: MNCV was abnormal in 30.4% of the subjects. Combining electrophysiological data we observed that:1. 28.6% of the subjects resulted normal2. 12.8% were affected by a lower limbs sensory neuropathy3. 0.2% had a lower limbs motor neuropathy4. 5.9% had a lower limbs sensory‐motor neuropathy5. 6.1% had a diffused sensory neuropathy6. 30.2% had a diffused sensory‐motor neuropathy7. 16.2% had a carpal tunnel syndrome.Patients were divided in 2 groups: patients with and patients without neuropahy: the latter showed a significantly shorter disease duration (12.7 ± 8.1 vs 9.0 ± 6.3; p < 0.0001).In addition, we observed a significant correlation between disease duration and distal latency, median and popliteal MNCV, and SNCV in median and sural nerve (Regression test; p < 0.0001).Patients on insulin showed a longer disease duration and more severe electrophysiological abnormalities.

Diagnostic criteria for demyelinating polyneuropathy associated with monoclonal gammopathy

In order to define diagnostic criteria for the demyelinating polyneuropathy associated with monoclonal gammopathy of undetermined significance (MGUS), we compared 30 patients with idiopathic chronic inflammatory demyelinating polyneuropathy (CIDP) without a monoclonal gammopathy, with 29 patients with polyneuropathy associated with MGUS. All 59 patients fulfilled research criteria for CIDP. In the patients with MGUS, sensory symptoms and signs predominated, there was usually no cranial nerve involvement, and the neuropathy was symmetrical with a slowly progressive course. On electrophysiological examination, an abnormal median nerve sensory action potential in combination with a normal sural nerve action potential (AMNS) was not found. In idiopathic CIDP patients, a preceding infection was frequent, motor features predominated, there was often cranial nerve involvement, the neuropathy could be asymmetrical, and AMNS was frequently found. Diagnostic criteria for demyelinating polyneuropathy associated with MGUS are presented. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 73–79, 2000

Dysfunction of small myelinated afferents in diabetic polyneuropathy, as assessed by laser evoked potentials

Objective: To verify whether laser evoked potentials are useful in assessing the function of small afferent fibers and to compare dysfunction of large and small afferent fibers in patients with diabetic polyneuropathy. Methods: The brain potentials evoked by CO 2 laser stimulation of the hand and foot were studied in diabetic patients ( n=45) with various degrees of peripheral nerve damage. Laser evoked potentials (which assess the function of small myelinated afferents) were also compared with ulnar and sural nerve sensory action potentials (which assess the function of large myelinated afferents) by scoring the abnormalities of the two neurophysiological tests with similar criteria. Results: Laser evoked potentials were often absent; the mean latency was normal and mean amplitude decreased, as expected in axonopathies. Although clinical examination showed more frequent impairment of vibratory than pinprick sensation, laser evoked potentials and sensory action potentials yielded similar abnormality scores and showed a strong intra-individual correlation. Conclusions: Laser evoked potentials, possibly better than standard clinical examination for assessing the abnormalities of small-diameter afferents, indicate that diabetic polyneuropathy induces large- and small-afferent dysfunction in parallel.

Electrophysiological deficiency in peripheral nerve induced by treatment for 12 weeks with 2-butenenitrile, 3-butenenitrile, cis-2-pentenenitrile and 3,3-iminodipropionitrile in rats.

Motor and sensory conduction velocities and amplitudes of the sensory and motor action potentials of the tail nerve were studied in male Sprague-Dawley rats during subchronic oral treatment with three unsaturated aliphatic nitriles. The rats were given, by gastric intubation, doses of 10, 20 and 40 mg x kg(-1) 3-butenenitrile (allyl cyanide) and 25, 50 and 100 mg x kg(-1) of either cis/trans-2-butenenitrile (crotononitrile) or cis-2-pentenenitrile once a day, 5 days per week for 12 weeks. Moreover, 3,3'-iminodipropionitrile was administered likewise at doses of 25, 50 and 100 mg x kg(-1) as reference neurotoxicant. Oral administration of the three unsaturated nitriles produced deafness and absence of reaction when the animals were subject to droptest. Moreover, rats exhibited both time- and concentration-dependent decreases in motor and sensory conduction velocities and amplitudes of the sensory action potentials. Nerve conduction velocities were partially reversible after 8 weeks of recovery. Rats receiving 3,3'-iminodipropionitrile developed deafness, head weaving and significant irreversive deficiencies in all the electrophysiological parameters studied. Further toxicological studies with related unsaturated nitriles should be carried out to determine the potential importance of the cis/trans isomerism in the observed neurotoxicity.

Neurophysiological evaluation of areflexia in Holmes-Adie syndrome

To evaluate ankle areflexia in Holmes-Adie syndrome (HAS). Hoffmann (H) and Tendon (T) soleus reflexes, tonic vibration reflex (TVR), and polysynaptic extension reflex of soleus muscle (PERS) were evaluated in eight patients with idiopathic HAS. Motor (MNCV) and sensory (SNCV) nerve conduction velocities, compound motor-action potential (CMAP), and sensory action potential (SAP) were also determined in upper and lower limbs. Soleus T reflex was obtained in one out of eight patients, and H-reflex was found in none of the patients. TVR was recorded in four out of eight patients, and PERS in all of the patients. MNCV, SNCV, CMAP and SAP showed normal values in all patients. In six out of the eight patients a late response following the tibial nerve stimulation showed constant latency, amplitude and morphology, with no recovery cycle or vibration inhibition. In this study, the neurophysiological spinal reflex circuitry evaluations support the view that HAS ankles areflexia is due to a selective impairement of monosynaptic connections of Ia afferents. A normal nuclear excitability is suggested by polysynaptic activation of the soleus motor nucleus.

Motor terminal latency index in carpal tunnel syndrome

We determined the motor terminal latency index (MTLI) of the median nerve across the carpal tunnel in 41 upper extremities of 31 patients with carpal tunnel syndrome. Changes in motor nerve conduction velocity (MNCV), motor terminal latency (MTL), sensory action potential and the amplitude of the compound muscle action potential recorded from the abductor pollicis brevis muscle were all suggestive of proximal and distal segment involvement of the nerve across the carpal tunnel. There was no correlation between forearm MNCV and MTL (r = 0.40), although MTLI was correlated with MTL (r = 0.67) but not with MNCV, indicating a disproportionate conduction across the carpal tunnel.

Peripheral neuropathy in systemic lupus erythematosus.

The prevalence of clinically apparent peripheral neuropathy in systemic lupus erythematosus is reported to be between 2% to 18%. The purpose of this prospective case-control study was to determine the prevalence of peripheral neuropathy (PN) using electrodiagnostic criteria. Subgroup analysis was performed to determine whether PN correlated with disease activity, renal involvement, or serum immune markers. Fifty-four systemic lupus erythematosus patients and 30 controls were recruited in the study. The right median, ulnar, peroneal, tibial, and sural sensory and motor nerve conduction studies were obtained. PN in our study was defined as any abnormal values in motor and sensory distal latency, sensory action potential, motor action potential, or conduction velocity affecting 2 or more nerves. Of the 54 patients studied, PN was present in 15 patients (27.8%) of which 4 were symptomatic. There was a significant correlation between PN and anti-SM antibody, and there was a trend showing decreased motor and sensory action potential amplitudes in our systemic lupus erythematosus group compared to the controls. This observation was also seen in an active disease group when compared to those with inactive disease. The amplitude of the action potential was more often affected than the distal latency, and sensory nerves were more susceptible than motor nerves. The sural sensory action potential amplitude appears to be the most sensitive indicator of PN which may be used as an index to monitor disease activity.

Alpha-lipoic acid provides neuroprotection from ischemia-reperfusion injury of peripheral nerve.

Reperfusion aggravates nerve ischemic fiber degeneration, likely by the generation of reduced oxygen species. We therefore evaluated if racemic alpha-lipoic acid (LA), a potent antioxidant, will protect peripheral nerve from reperfusion injury, using our established model of ischemia-reperfusion injury. We used male SD rats, 300+/-5 g. Ischemia was produced by the ligature of each of the supplying arteries to the sciatic-tibial nerve of the right hind-limb for predetermined periods of time (either 3 or 5 h), followed by the release of the ligatures, resulting in reperfusion. LA was given intraperitoneally daily for 3 days for both pre- and post-surgery. Animals received either LA, 100 mg/kg/day, or the same volume of saline intraperitoneally. Clinical behavioral score and electrophysiology of motor and sensory nerves were obtained at 1 week after ischemia-reperfusion. After electrophysiological examination, the sciatic-tibial nerve was fixed in situ and embedded in epon. We evaluated for ischemic fiber degeneration (IFD) and edema, as we described previously. Distal sensory conduction (amplitude of sensory action potential and sensory conduction velocity (SCV) of digital nerve) was significantly improved in the 3-h ischemia group, treated with LA (P<0.05). LA also improved IFD of the mid tibial nerve (P=0.0522). LA failed to show favorable effects if the duration of ischemia was longer (5-h ischemia). These results suggest that alpha-lipoic acid is efficacious for moderate ischemia-reperfusion, especially on distal sensory nerves.

Pitfalls in using the ring finger test alone for the diagnosis of carpal tunnel syndrome.

Latency differences (>0.5 ms) of median and ulnar sensory action potentials (mSAP and uSAP) at the wrist evoked by ring finger stimulation are considered a sensitive and specific test for diagnosis of carpal tunnel syndrome (CTS). In this study, we aimed to assess the practical usefulness of the ring finger test (RFT) in routine electromyography (EMG) examinations. We investigated 2 series of patients: in the first prospective series we considered 300 hands affected by only mild CTS; in the second series we examined retrospectively the EMG charts of 961 hands affected only by CTS but not selected for severity or duration of symptoms. In the first series we found pathological RFT scores in 87% of cases, and pathological RFT or mSAP latency results in 92%. In the second series, pathological RFT scores were found only in 55% of cases, while in 20% where mSAP failed, a volume conducted uSAP had been erroneously interpreted as arising from the median nerve. RFT sensitivity tested in routine EMG examinations of unselected hands affected by CTS drops considerably. Fingers innervated by one only nerve, such as the index and the little fingers, must also be investigated to increase the diagnostic value of RFT.

Relationships between Clinical Scales on Severity of Symptoms and Electrodiagnostic Measures on Abnormality of Nerve Conduction in Carpal Tunnel Syndrome

This study examined the severity of carpal tunnel syndrome symptoms in relation to nerve conduction measures of the median nerve. The symptom scales include (1) numbness, (2) tingling, (3) nocturnal symptoms, (4) pain, (5) weakness, and (6) clumsiness; the nerve conduction measures are (1) peak amplitude and (2) peak latency of the sensory action potential, (3) conduction velocity of the sensory nerve fibers, (4) peak amplitude and (5) onset latency of the motor action potential. The symptom severity and nerve conduction impairment were evaluated for 34 affected hands of 24 patients (6 males and 18 females) by using a questionnaire developed by Levine et al. and an electromyographic instrument, respectively. Significant relationships identified among the clinical scales resulted in a dichotomous symptom classification scheme with a criterion of the relatedness to nerve damage: primary and secondary symptoms. Correlation analysis on the symptom and electrodiagnostic measures showed both the severity scales for the primary and all the symptoms had higher correlations with the extent of the nerve injury than that for the secondary symptoms. These results demonstrated a biological significance of the clinical scales, which can be used in evaluating the outcome of treatments and developing a model for exposure-severity relationship.

Quantitative description of the voltage dependence of axonal excitability in human cutaneous afferents.

The voltage dependence of indices of axonal excitability were quantified for cutaneous afferents in eight normal subjects, using the threshold for a target compound sensory action potential as a measure of membrane potential. The membrane potential was altered using subthreshold depolarizing and hyperpolarizing currents of various sizes (-50% to +50% of threshold). Refractoriness and supernormality were determined as the threshold change required to produce the target potential when preceded by a supramaximal stimulus at appropriate conditioning-test intervals. The strength-duration time constant (tauSD) was calculated from the threshold currents using unconditioned test stimuli of 0.1 and 1 ms. There was a near-linear relationship between each of these indices and the reciprocal of threshold (a measure of 'excitability'). It is argued that the voltage dependencies of refractoriness and tauSD largely reflect the behaviour of transient and persistent Na+ channels, respectively, and that the present data therefore quantify aspects of Na+ channel behaviour in human nerves.

Clinical and electrophysiological findings and follow-up in tarsal tunnel syndrome

The authors report clinical and electrophysiological findings in 59 patients with tarsal tunnel syndrome (TTS) and follow-up in 23 of them. The entrapment was prevalent in females; was bilateral in 6 patients and involved medial plantar in 7 and lateral plantar nerves in two cases. Eleven presented with other nerve entrapment syndromes or focal mononeuropathies, due to hereditary neuropathy with liability to pressure palsy or systemic diseases. The other 48 subjects had TTS without any other related entrapment syndromes: 23 were idiopathic cases, 13 had a history of local trauma, 3 had systemic diseases and the others had external or intrinsic compressions. The most frequent symptoms were paraesthesia or dysaesthesia (86% of feet) and pain (55%). Hypoaesthesia of the sole and weakness of toe flexion were evident in 74% and 22% of feet, respectively. Absence of sensory action potential or slowing of sensory conduction velocity (SCV) of the plantar nerves were present in 77% of feet; significant differences of SCV between affected and unaffected plantar nerves and/or between distal sural and plantar nerves were evident in 14%. Abnormalities of plantar SCV were therefore absent in only 9% of feet. Distal motor latency was delayed in 55% and electromyography showed neurogenic changes in 45% of sole muscles. Five cases (6 feet) underwent surgery with excellent or good results in 5, 4 of them also showing improvement in distal conduction of the plantar nerves. Nine were treated with local steroid injections, with good results shown in 6 patients. Nine other patients who did not receive any therapy showed a disappearance of symptoms or good outcome in 6 cases. The subjects with poor therapeutic results had S1 radiculopathy or systemic diseases. The authors underline that patients with connective tissue diseases should not be treated by surgical decompression because they may have subclinical neuropathy. Some subjects with idiopathic or trauma-induced TTS recover spontaneously. Surgical release should be limited to cases with space-occupying lesions and when conservative treatments fail.

Patterns of neurophysiological abnormality in prolonged critical illness.

To describe the various patterns of neurophysiological abnormalities which may complicate prolonged critical illness and identify possible aetiological factors. Prospective case series of neurophysiological studies, severity of illness scores, organ failures, drug therapy and hospital outcome. Some patients also had muscle biopsies. General intensive care unit (ICU) in a University Hospital. Forty-four patients requiring intensive care unit stay of more than 7 days. The median age was 60 (range 27-84 years), APACHE II score 19 (range 8-33), organ failures 3 (range 1-6), and mortality was 23%. Seven patients had normal neurophysiology (group I), 4 had a predominantly sensory axonal neuropathy (group II), 11 had motor syndromes characterised by markedly reduced compound muscle action potentials and sensory action potentials in the normal range (group III) and 19 had combinations of motor and sensory abnormalities (group IV). Three patients had abnormal studies but could not be classified into the above groups (group V). All patients had normal nerve conduction velocities. Electromyography revealed evidence of denervation in five patients in group III and five in group IV. There was no obvious relationship between the pattern of neurophysiological abnormality and the APACHE II score, organ failure score, the presence of sepsis or the administration of muscle relaxants and steroids. A wide range of histological abnormalities was seen in the 24 patients who had a muscle biopsy; there was no clear relationship between these changes and the neurophysiological abnormalities, although histologically normal muscle was only found in patients with normal neurophysiology. Only three of the eight patients from group III in whom muscle biopsy was performed had histological changes compatible with myopathy. Neurophysiological abnormalities complicating critical illness can be broadly divided into three types -- sensory abnormalities alone, a pure motor syndrome and a mixed motor and sensory disturbance. The motor syndrome could be explained by an abnormality in the most distal portion of the motor axon, at the neuromuscular junction or the motor end plate and, in some cases, by inexcitable muscle membranes or extreme loss of muscle bulk. The mixed motor and sensory disturbance which is characteristic of 'critical illness polyneuropathy' could be explained by a combination of the pure motor syndrome and the mild sensory neuropathy. More precise identification of the various neurophysiological abnormalities and aetiological factors may lead to further insights into the causes of neuromuscular weakness in the critically ill and ultimately to measures for their prevention and treatment.

Electrophysiological and nerve biopsy: comparative study in Friedreich's ataxia and Friedreich's ataxia phenotype with vitamin E deficiency

The authors report a comparative study of peripheral nerve conductions and nerve biopsy and somatosensory evoked potentials between 15 patients with Friedreich's ataxia and 15 patients with Friedreich's ataxia phenotype with selective vitamin E deficiency. The patients in the two groups are of similar age, age of onset, and clinical phenotype. Peripheral motor nerve action potential amplitude, and conduction velocities are within normal ranges in the two groups. In the Friedreich's ataxia group there is an early and severe peripheral sensory axonal neuronopathy, characterised by an important reduction of the amplitude of sensory action potential, and important loss of myelinated fibres with complete disappearance of large myelinated fibres without any regenerative process. In the Friedreich's ataxia phenotype with selective vitamin E deficiency group there is slight-to-moderate axonal sensory neuropathy with normal to moderate decrease of large myelinated fibre density and important regeneration in nerve biopsy. Somatosensory evoked potentials are markedly involved in the two groups asserting a severe involvement of somatosensory pathway in lumbar, thoracic and cervical spinal cord. These findings suggest that the pathological mechanism involved in the two diseases are different: central peripheral axonopathy in Friedreich's ataxia and central distal axonopathy in Friedreich's ataxia phenotype with selective vitamin E deficiency.

Different indentation velocities activate different populations of mechanoreceptors in humans.

We have examined whether different skin machanoreceptors are activated by different indentation velocities of a tactile probe. Indentations of 300 microns at velocities of 100 and 400 microns/ms were applied at the dorsolateral side of the foot and at the tip of digit III. Compound sensory action potentials (CSAPs) were recorded from the sural and median nerves, respectively. The amplitudes of the tactile CSAPs were < 1-2 muV, and less than 15% of the CSAPs evoked by electrical stimulation. The areas of the polyphasic tactile CSAPs were 35-38% smaller at 100 microns/ms than at 400 microns/ms. The maximal sensory nerve conduction velocities (SNCVs) were higher in the median than in the sural nerves. In both nerves, the SNCVs were similar at electrical and 400-micron/ms tactile stimulation but 11-17% lower at 100-micron/ms stimulation. Cocaine hydrochloride was applied iontophoretically at the dorsolateral side of the foot, causing a decrease of 50% of the CSAP evoked by 100 microns/ms but only 14% at 400 microns/ms. These studies suggested that identation at 400 microns/ms activated mainly deeply placed (Pacini corpuscles) and to some extent superficial mechanoreceptors, whereas the 100-micron/ms indentation activated primarily superficially situated receptors (Meissner corpuscles, and some slowly adapting units).

Observations on Severe Ulnar Neuropathy in Diabetes

We describe the clinical and neurophysiologic findings in a group of diabetic patients with a severe ulnar neuropathy. All patients attending a large inner-city diabetes center were prospectively screening for hand wasting and weakness due to ulnar nerve disease. Twenty diabetic patients fulfilling the clinical criteria underwent nerve conduction studies and electromyography. All but one patient with a motor ulnar neuropathy had systemic complications, mostly severe: ten were amputees, four had had a renal transplant, and two were blind. The onset of hand weakness was sudden in five. All patients had a classical “ulnar hand” (bilateral in five) but forearm muscles were little affected. Sensory loss was prominent in only one-half. Nerve conduction studies showed markedly reduced ulnar motor responses (mean, 1.2 mV versus 7.4 mV in controls) and ulnar/median motor ratios. Motor conduction was disproportionately slowed across the elbows, with or without conduction block, in only eight of 34 affected ulnar nerves. Five of these patients had a habit of leaning on their elbows and/or a Tinel’s sign. Median sensory action potentials (SAPs) were recordable in 12 patients but ulnar SAPs were absent in 30 of 34 affected nerves. Electromyography revealed advanced denervation of ulnar supplied hand muscles. We conclude that motor ulnar neuropathy is not uncommon in patients with diabetes of long standing, especially in those with severe systemic complications. Nerve entrapment at the elbows occurs in some, but in many the lesion is axonal, and damage may occur through ischemia.

An unusual cause of peripheral neuropathy.

A 74-year-old man presented with a 2-month history of weight gain, lethargy and cold intolerance. He had had endoscopic retrograde cholangiopancreatography (ERCP) 3 years prior to admission. His free thyroxine...

Electroneurographic investigation of the mandibular nerve in lingual neuropathy.

We developed a method for determination of motor conduction along the mandibular and sensory conduction along the lingual and inferior alveolar nerves in 10 controls and 6 patients with lingual neuropathy following lower wisdom tooth extraction. Patients with lingual neuropathy had reduced/absent or delayed compound sensory action potentials and normal conduction along the fibers of the inferior alveolar nerve and mandibular nerve. The method provides a useful electrophysiological means of evaluating lingual nerve lesions.

Correlation of peripheral nerve fiber loss and trinucleotide repeats in Machado-Joseph disease.

Machado-Joseph disease (MJD) is a dominantly inherited cerebellar ataxia associated with spasticity, ophthalmoplegia and dystonia. There has been no report of electrophysiological or histological alterations of the peripheral nervous system in patients with MJD. Four patients with MJD were identified by polymerase chain reaction. The peripheral nerves of these patients were subjected to electrophysiological testing and histological study. Correlation analyses were made between various clinical parameters and the electrophysiological and histological changes. Electrophysiological studies demonstrated a marked reduction of sensory action potential, acute denervation changes on needle EMG, as well as mild decrease in the compound motor action potential. Light microscopy of the sural nerves revealed clear loss of myelinated fibers, and morphometry studies showed a loss of large myelinated fibers. Moreover, the severity of these pathological changes was found to be related to the CAG repeat length in the MJD gene. Our findings indicated that the peripheral nervous system was frequently affected in patients with MJD. These findings were similar to those seen in Friedreich's ataxia, suggesting a loss of sensory and motor fibers probably following a lesion of the dorsal root ganglion and the anterior horns in the spinal cord. Furthermore, the number of CAG repeats seems to have an inverse relationship to the extent of pathological changes of the peripheral nerves.

Hereditary motor and sensory neuropathy with deafness, mental retardation, and absence of sensory large myelinated fibers: Confirmation of a new entity

We describe two brothers, 11 and 13 years old, respectively, with an early-onset hereditary motor and sensory neuropathy, deafness, and mental retardation. Electrophysiological studies showed marked reduction of motor and sensory conduction velocity and absence of sensory action potentials. Sural nerve biopsy, performed in both patients, showed absence of large myelinated fibers with normal density of small myelinated fibers without axonal degeneration. Signs of demyelination were found only in the younger patient. We suggest that motorsensory neuropathy associated with deafness and mental retardation with absence of large myelinated fibers on sural nerve biopsy represents a distinct clinicopathological entity, which is transmitted in families probably as an autosomal recessive trait.