Extent, impact, and predictors of diagnostic delay in Pompe disease: A combined survey approach to unveil the diagnostic odyssey

BACKGROUND

Early diagnosis is of substantial benefit for patients with Pompe disease. Yet underdiagnosing and substantial diagnostic delay are still frequent and the determinants of this are unknown. This study is the first to systematically investigate the diagnostic odyssey in Pompe disease from patients', parents', and physicians' perspectives.

METHODS

Patients with infantile or late onset Pompe disease, their parents as well as their metabolic experts were invited to fill in respective surveys. The survey addressed perceived disease symptoms at onset and during the course of the disease, specialties of involved physicians, activities of patient-initiated search for diagnosis and the perceived impact of time to diagnosis on outcome. Results of experts' and patients'/parents' surveys were compared and expressed by descriptive statistics.

RESULTS AND DISCUSSION

We collected data on 15 males and 17 females including 9 infantile and 23 late onset Pompe patients. All received the correct diagnosis at a metabolic or musculoskeletal expert center. Patients with direct referral to the expert center had the lowest diagnostic delay, while patients who were seen by several physicians, received the correct diagnosis after 44%-200% longer delay. The proportion of direct referral varied strongly between pediatricians (57%) and other disciplines (18%-36%).

CONCLUSION

Our study highlights a substantially larger diagnostic delay in Pompe patients that are not directly referred to expert centers for diagnostic work. Our findings may be used to develop more successful strategies for early diagnosis.

SYNOPSIS

Diagnostic delay in Pompe disease is substantial particularly in patients that are not directly referred to expert centers for diagnostic workup, so facilitating direct referral may be a new strategy for early diagnosis.

Nutrient pattern analysis in critically ill patients using Omics technology (NAChO) - Study protocol for a prospective observational study

INTRODUCTION

Intensive care unit-acquired weakness (ICU-AW) is often observed in critically ill patients with prolonged intensive care unit (ICU) stay. We hypothesized that evolving metabolic abnormalities during prolonged ICU stay are reflected by changing nutrient patterns in blood, urine and skeletal muscle, and that these patterns differ in patients with/without ICU-AW and between patients with/without sepsis.

METHODS

In a prospective single-center observational trial, we aim to recruit 100 critically ill patients (ICU length of stay ≥ 5 days) with severe sepsis/septic shock ("sepsis group", n = 50) or severe head trauma/intracerebral hemorrhage ("CNS group", n = 50). Patients will be sub-grouped for presence or absence of ICU-AW as determined by the Medical Research Council sum score. Blood and urine samples will be collected and subjected to comprehensive nutrient analysis at different time points by targeted quantitative mass spectrometric methods. In addition, changes in muscular tissue (biopsy, when available), muscular architecture (ultrasound), electrophysiology, body composition analyses (bioimpedance, cerebral magnetic resonance imaging), along with clinical status will be assessed. Patients will be followed-up for 180 and 360 days including assessment of quality of life.

DISCUSSION

Key objective of this trial is to assess changes in nutrient pattern in blood and urine over time in critically ill patients with/without ICU-AW by using quantitative nutrient analysis techniques. Peer-reviewed published NAChO data will allow for a better understanding of metabolic changes in critically ill patients on standard liquid enteral nutrition and will likely open up new avenues for future therapeutic and nutritional interventions.

Loss of tubulin deglutamylase CCP1 causes infantile-onset neurodegeneration

A set of glutamylases and deglutamylases controls levels of tubulin polyglutamylation, a prominent post-translational modification of neuronal microtubules. Defective tubulin polyglutamylation was first linked to neurodegeneration in the Purkinje cell degeneration (pcd) mouse, which lacks deglutamylase CCP1, displays massive cerebellar atrophy, and accumulates abnormally glutamylated tubulin in degenerating neurons. We found biallelic rare and damaging variants in the gene encoding CCP1 in 13 individuals with infantile-onset neurodegeneration and confirmed the absence of functional CCP1 along with dysregulated tubulin polyglutamylation. The human disease mainly affected the cerebellum, spinal motor neurons, and peripheral nerves. We also demonstrate previously unrecognized peripheral nerve and spinal motor neuron degeneration in pcd mice, which thus recapitulated key features of the human disease. Our findings link human neurodegeneration to tubulin polyglutamylation, entailing this post-translational modification as a potential target for drug development for neurodegenerative disorders.

Cessation and resuming of alglucosidase alfa in Pompe disease: a retrospective analysis

Enzyme replacement therapy (ERT) with recombinant human alglucosidase alfa (rhGAA) in late-onset Pompe disease is moderately effective. Little is known about the clinical course after treatment termination and the resumption of ERT. In Switzerland, rhGAA therapy for Pompe disease was temporarily withdrawn after the federal court judged that the treatment costs were greatly out of proportion compared to the benefits. Re-treatment was initiated after the therapy was finally licensed. We retrospectively analysed seven Pompe patients, who underwent cessation and resumption of ERT (median age 43 years). The delay from first symptoms to final diagnosis ranged from 4 to 20 years. The demographics, clinical characteristics, assessments with the 6-min walking test (6-MWT), the predicted forced vital capacity (FVC) and muscle strength were analysed. Before initiation of ERT, all patients suffered from proximal muscle weakness of the lower limbs; one was wheelchair-bound and two patients received night-time non-invasive ventilation. Initial treatment stabilised respiratory function in most patients and improved their walking performance. After treatment cessation, upright FVC declined in most and the 6-MWT declined in all patients. Two patients needed additional non-invasive ventilatory support. Twelve months after resuming ERT, the respiratory and walking capacity improved again in most patients. However, aside for one patient, none of the patients reached the same level of respiratory function or distance walked in 6 min, as at the time of ERT withdrawal. We conclude that cessation of ERT in Pompe disease causes a decline in clinical function and should be avoided. Resuming treatment only partially recovers respiratory function and walking capacity.

The latency distribution of motor evoked potentials in patients with multiple sclerosis

OBJECTIVE

To compare the individual latency distributions of motor evoked potentials (MEP) in patients with multiple sclerosis (MS) to the previously reported results in healthy subjects (Firmin et al., 2011).

METHODS

We applied the previously reported method to measure the distribution of MEP latencies to 16 patients with MS. The method is based on transcranial magnetic stimulation and consists of a combination of the triple stimulation technique with a method originally developed to measure conduction velocity distributions in peripheral nerves.

RESULTS

MEP latency distributions in MS typically showed two peaks. The individual MEP latency distributions were significantly wider in patients with MS than in healthy subjects. The mean triple stimulation delay extension at the 75% quantile, a proxy for MEP latency distribution width, was 7.3 ms in healthy subjects and 10.7 ms in patients with MS.

CONCLUSIONS

In patients with MS, slow portions of the central motor pathway contribute more to the MEP than in healthy subjects. The bimodal distribution found in healthy subjects is preserved in MS.

SIGNIFICANCE

Our method to measure the distribution of MEP latencies is suitable to detect alterations in the relative contribution of corticospinal tract portions with long MEP latencies to motor conduction.

Corticospinal output during muscular fatigue differs in multiple sclerosis patients compared to healthy controls

Background:

In multiple sclerosis (MS), fatigue is a common and often disabling symptom. It has multiple causes with central motor fatigue playing an important role.

Objective:

The objective of this study was to analyse the central motor conduction changes in relation to muscle contraction force during muscle fatigue and recovery in MS patients compared to healthy controls.

Methods:

A total of 23 MS patients with fatigue and 13 healthy subjects were assessed during 2 minutes of fatiguing exercise of the abductor digiti minimi muscle of the hand and the subsequent 7 minutes of recovery. Central motor conduction was quantified by transcranial magnetic stimulation using the triple stimulation protocol and calculating a central conduction index (CCI).

Results:

Force declined to 36% of the pre-exercise level (SD 16%; p < 0.01) in MS patients and to 44% (SD 9%, p < 0.01) in healthy subjects (group differences, not statistically significant). The decline of the CCI was significantly less marked in patients (–20%, SD 26%, p < 0.05) than in healthy subjects (–57%, SD 15%, p < 0.05; group differences, p < 0.05). The decline of force and CCI were not correlated in either group.

Conclusions:

During a fatiguing exercise, the decline in central motor conduction is significantly less pronounced in MS patients than healthy subjects, although the reduction of force is similar.

Reproducibility of sensory nerve conduction studies of the sural nerve using ultrasound-guided needle positioning

INTRODUCTION

In this study we sought to evaluate the reproducibility of sensory nerve conduction studies (NCS) using ultrasound-guided needle positioning (USNP).

METHODS

Orthodromic NCS of the sural nerve using needle electrodes with USNP as well as surface electrodes were conducted twice in 20 healthy volunteers.

RESULTS

The mean sensory nerve action potential (SNAP) amplitude in the initial examination was 39.5 μV using needle electrodes with USNP, and 12.5 μV using surface electrodes (P < 0.0001). The mean SNAP amplitude in the follow-up examination was 39.2 μV using needle electrodes with USNP, and 12.4 μV using surface electrodes (P < 0.0001). The mean intraindividual change in SNAP amplitude (test-retest) was 21.2% using needle electrodes with USNP, and 24.8% using surface electrodes (P = 0.6).

CONCLUSIONS

Sensory NCS of the sural nerve using needle electrodes with USNP have reliable test-retest reproducibility and yield greater SNAP amplitudes than sensory NCS using surface electrodes.

A method to measure the distribution of latencies of motor evoked potentials in man

OBJECTIVE

To measure the intra-individual distribution of the latencies of motor evoked potentials (MepL) using transcranial magnetic stimulation.

METHODS

We used the triple stimulation technique (TST) to quantify the proportion of excited spinal motor neurons supplying the abductor digiti minimi muscle in response to a maximal magnetic brain stimulus (Magistris et al., 1998). By systematically manipulating the TST delay, we could quantify the contribution of slow-conducting motor tract portions to the TST amplitude.

RESULTS

Our method allowed the establishment of a MepL distribution for each of the 29 examined healthy subjects. MepLs of 50% of the motor tract contributing to the motor evoked potential laid between the intra-individually minimal MepL (MepL(min)) and MepL(min)+4.9 ms (range 1.6-9.2). The individual MepL distributions showed two peaks in most subjects. The first peak appeared at a MepL that was 3.0 ms longer on average (range 0.7-6.0) than MepL(min); the second peak appeared at MepL(min)+8.1 ms on average (range 3.7-13.0).

CONCLUSIONS

Slow-conducting parts of the motor pathway contribute notably to the motor evoked potential. Our data suggest a bimodal distribution of central conduction times, which might possibly relate to different fibre types within the pyramidal tract.

SIGNIFICANCE

We present a non-invasive method to assess slow-conducting parts of the human central motor tract.

Ultrasound-guided needle positioning in sensory nerve conduction study of the sural nerve

OBJECTIVES

To evaluate the usefulness of ultrasound imaging to improve the positioning of the recording needle for nerve conduction studies (NCS) of the sural nerve.

METHODS

Orthodromic NCS of the sural nerve was performed in 44 consecutive patients evaluated for polyneuropathy. Ultrasound-guided needle positioning (USNP) was compared to conventional "blind" needle positioning (BNP), electrically guided needle positioning (EGNP), and to recordings with surface electrodes (SFN).

RESULTS

The mean distance between the needle tip and the nerve was 1.1 mm with USNP compared to 5.1 mm with BNP (p<0.0001). The mean amplitude of the sensory nerve action potential (SNAP) was 21 microV with USNP and 11 microV with BNP (p<0.0001). Compared to BNP, nerve-needle distances and SNAP amplitudes did not improve with EGNP. SNAP amplitudes recorded with SFN were significantly smaller than with BNP, EGNP and USNP.

CONCLUSION

Ultrasound increases the precision of needle positioning markedly, compared to conventional methods. The amplitude of the recorded SNAP is usually clearly greater using USNP. In addition, USNP is faster, less painful and less dependent on the patient.

SIGNIFICANCE

USNP is superior to BNP, EGNP, and SFN in accurate measurement of SNAP amplitude. It has a potential use in the routine near-nerve needle sensory NCS of pure sensory nerves.

Anti-myelin antibodies in clinically isolated syndrome indicate the risk of multiple sclerosis in a Swiss cohort

OBJECTIVES

In patients with a clinically isolated syndrome (CIS), the time interval to convert to clinically definite multiple sclerosis (CDMS) is highly variable. Individual and geographical prognostic factors remain to be determined. Whether anti-myelin antibodies may predict the risk of conversion to CDMS in Swiss CIS patients of the canton Berne was the subject of the study.

METHODS

Anti-myelin oligodendrocyte glycoprotein and anti-myelin basic protein antibodies were determined prospectively in patients admitted to our department.

RESULTS

After a mean follow-up of 12 months, none of nine antibody-negative, but 22 of 30 antibody-positive patients had progressed to CDMS. Beta-Interferon treatment delayed the time to conversion from a mean of 7.4 to 10.9 months.

CONCLUSIONS

In a Swiss cohort, antibody-negative CIS patients have a favorable short-term prognosis, and antibody-positive patients benefit from early treatment.

Muscle Metabolites: Functional MR Spectroscopy during Exercise Imposed by Tetanic Electrical Nerve Stimulation

Permission from the ethics committee and informed consent were obtained. The purpose of this study was to prospectively evaluate a method developed for the noninvasive assessment of muscle metabolites during exercise. Hydrogen 1 magnetic resonance (MR) spectroscopy peaks were measured during tetanic isometric muscle contraction imposed by supramaximal repetitive nerve stimulation. The kinetics of creatine-phosphocreatine and acetylcarnitine signal changes (P < .001) could be assessed continuously before, during, and after exercise. The control peak (trimethylammonium compounds), which served as an internal reference, did not change. This technique-that is, functional MR spectroscopy-opens the possibility for noninvasive diagnostic muscle metabolite testing in a clinical setting.

Quantification of central motor conduction deficits in multiple sclerosis patients before and after treatment of acute exacerbation by methylprednisolone

OBJECTIVE

To compare the effects of intravenous methylprednisolone (IVMP) in patients with relapsing-remitting (RR-MS), secondary progressive (SP-MS), and primary progressive multiple sclerosis (PP-MS).

METHODS

Clinical and neurophysiological follow up was undertaken in 24 RR-MS, eight SP-MS, and nine PP-MS patients receiving Solu-Medrol 500 mg/d over five days for exacerbations involving the motor system. Motor evoked potentials (MEPs) were used to measure central motor conduction time (CMCT) and the triple stimulation technique (TST) was applied to assess conduction deficits. The TST allows accurate quantification of the number of conducting central motor neurones, expressed by the TST amplitude ratio.

RESULTS

There was a significant increase in TST amplitude ratio in RR-MS (p<0.001) and SP-MS patients (p<0.02) at day 5, paralleling an increase in muscle force. TST amplitude ratio and muscle force remained stable at two months. In PP-MS, TST amplitude ratio and muscle force did not change. CMCT did not change significantly in any of the three groups.

CONCLUSIONS

In RR-MS and SP-MS, IVMP is followed by a prompt increase in conducting central motor neurones paralleled by improvement in muscle force, which most probably reflects partial resolution of central conduction block. The lack of similar clinical and neurophysiological changes in PP-MS corroborates previous clinical reports on limited IVMP efficacy in this patient group and points to pathophysiological differences underlying exacerbations in PP-MS.

Repetitive spinal motor neuron discharges following single transcranial magnetic stimuli: a quantitative study

OBJECTIVE

To quantify repetitive discharges of spinal motor neurons (repMNDs) in response to single transcranial magnetic stimuli (TMS). To assess their contribution to the size of motor evoked potentials (MEPs).

METHODS

We combined the triple stimulation technique (TST) with an additional nerve stimulus in the periphery (= quadruple stimulation; QuadS). The QuadS eliminates the first action potential descending on each axon after TMS, and eliminates effects on response size induced by desynchronization of these discharges, thereby allowing a quantification of motor neurons (MNs) discharging twice. In some instances, a quintuple stimulation (QuintS) was used, to quantify the number of MNs discharging three times. Recordings were from the abductor digiti minimi of 14 healthy subjects, using two different stimulation intensities and three different levels of facilitatory muscle pre-contractions.

RESULTS

The threshold to obtain repMNDs was high. Their maximal size differed markedly between subjects, ranging from 8 to 52% of all MNs. Stimulation intensity and facilitatory muscle contraction, but not resting motor threshold, correlated with the amount of repMNDs. QuintS never yielded discernible responses, hence all observed repMNDs were double discharges. RepMNDs contributed to the MEP areas, but did not influence MEP amplitudes.

CONCLUSIONS

QuadS and QuintS allow precise quantification of repMNDs. The threshold of repMNDs is high and varies considerably between subjects.

SIGNIFICANCE

repMNDs have to be considered when MEP areas are measured. Their analysis may be of interest in neurological disorders, but standardized stimulation parameters appear essential.

Uncrossed cortico-muscular projections in humans are abundant to facial muscles of the upper and lower face, but may differ between sexes

It is a popular concept in clinical neurology that muscles of the lower face receive predominantly crossed cortico-bulbar motor input, whereas muscles of the upper face receive additional ipsilateral, uncrossed input. To test this notion, we used focal transcranial magnetic brain stimulation to quantify crossed and uncrossed cortico-muscular projections to 6 different facial muscles (right and left Mm. frontalis, nasalis, and orbicularis oris) in 36 healthy right-handed volunteers (15 men, 21 women, mean age 25 years). Uncrossed input was present in 78% to 92% of the 6 examined muscles. The mean uncrossed: crossed response amplitude ratios were 0.74/0.65 in right/left frontalis, 0.73/0.59 in nasalis, and 0.54/0.71 in orbicularis oris; ANOVA p>0.05). Judged by the sizes of motor evoked potentials, the cortical representation of the 3 muscles was similar. The amount of uncrossed projections was different between men and women, since men had stronger left-to-left projections and women stronger right-to-right projections. We conclude that the amount of uncrossed pyramidal projections is not different for muscles of the upper from those of the lower face. The clinical observation that frontal muscles are often spared in central facial palsies must, therefore, be explained differently. Moreover, gender specific lateralization phenomena may not only be present for higher level behavioural functions, but may also affect simple systems on a lower level of motor hierarchy.

Assessment of central motor conduction to intrinsic hand muscles using the triple stimulation technique: normal values and repeatability

OBJECTIVE

To establish the triple stimulation technique (TST) for recordings from the first dorsal interosseus (FDI) and the abductor pollicis brevis muscles (APB), and to analyse the test-retest repeatability of the TST measurements in APB.

METHODS

The recently developed TST was slightly modified for recordings from small hand muscles to account for volume conducted activity from surrounding muscles. The TST combines transcranial magnetic stimulation (TMS) with a peripheral collision technique [Magistris et al. Brain 121 (1998) 437]. In contrast to conventional motor-evoked potentials (MEPs), it quantifies the number of conducting central motor neurons (expressed by the TST amplitude ratio, TST-AR). MEPs and TST were performed in 30 sides of 25 healthy subjects (target muscle FDI), and in 29 sides of 21 healthy subjects (target muscle APB). All APB recordings were repeated after 25+/-5.9 days.

RESULTS

The TST-AR averaged 97.4+/-2.5% in FDI and 95.9+/-4.7% in APB. There was a mean difference of the TST-AR ratio of 2.9+/-3.1% between the repeated APB recordings (95% limits of agreement+/-6.3%).

CONCLUSIONS

TMS allows activation of virtually all motor neurons supplying FDI and APB, when effects of volume conduction are eliminated. Its test-retest repeatability is excellent.

SIGNIFICANCE

The TST is well suited for follow-up examinations of central motor conduction failures. The greater number of established target muscles widens its clinical applicability.

Quantification of Uhthoff's phenomenon in multiple sclerosis: a magnetic stimulation study

OBJECTIVE

To quantify temperature induced changes (=Uhthoff phenomenon) in central motor conduction and their relation to clinical motor deficits in 20 multiple sclerosis (MS) patients.

METHODS

Self-assessment of vulnerability to temperature and clinical examination were performed. We used motor evoked potentials to measure central motor conduction time (CMCT) and applied the triple stimulation technique (TST) to assess conduction failure. The TST allows an accurate quantification of the proportion of conducting central motor neurons, expressed by the TST amplitude ratio (TST-AR).

RESULTS

Temperature induced changes of TST-AR were significantly more marked in patients with prolonged CMCT (P=0.037). There was a significant linear correlation between changes of TST-AR and walking velocity (P=0.0002). Relationships were found between pronounced subjective vulnerability to temperature and (i) abnormal CMCT (P=0.02), (ii) temperature induced changes in TST-AR (P=0.04) and (iii) temperature induced changes in walking velocity (P=0.04). CMCT remained virtually unchanged by temperature modification.

CONCLUSIONS

Uhthoff phenomena in the motor system are due to varying degrees of conduction block and associated with prolonged CMCT. In contrast to conduction block, CMCT is not importantly affected by temperature.

SIGNIFICANCE

This is the first study quantifying the Uhthoff phenomenon in the pyramidal tract of MS patients. The results suggest that patients with central conduction slowing are particularly vulnerable to develop temperature-dependent central motor conduction blocks.

Impact of coil position and electrophysiological monitoring on determination of motor thresholds to transcranial magnetic stimulation

OBJECTIVE

We compared motor and movement thresholds to transcranial magnetic stimulation (TMS) in healthy subjects and investigated the effect of different coil positions on thresholds and MEP (motor-evoked potential) amplitudes.

METHODS

The abductor pollicis brevis (APB) 'hot spot' and a standard scalp position were stimulated. APB resting motor threshold (APB MEP-MT) defined by the '5/10' electrophysiological method was compared with movement threshold (MOV-MT), defined by visualization of movements. Additionally, APB MEP-MTs were evaluated with the '3/6 method,' and MEPs were recorded at a stimulation intensity of 120% APB MEP-MT at each position.

RESULTS

APB MEP-MTs were significantly lower by stimulation of the 'hot spot' than of the standard position, and significantly lower than MOV-MTs (n=15). There were no significant differences between the '3/6' and the '5/10' methods, or between APB MEP amplitudes by stimulating each position at 120% APB MEP-MT.

CONCLUSIONS

Coil position and electrophysiological monitoring influenced motor threshold determinations. Performing 6 instead of 10 trials did not produce different threshold measurements. Adjustment of intensity according to APB MEP-MT at the stimulated position did not influence APB MEP amplitudes.

SIGNIFICANCE

Standardization of stimulation positions, nomenclature and criteria for threshold measurements should be considered in design and comparison of TMS protocols.

Significance of coil orientation for motor evoked potentials from nasalis muscle elicited by transcranial magnetic stimulation

OBJECTIVE

In transcranial magnetic stimulation (TMS) of the motor cortex, the optimal orientation of the coil on the scalp is dependent on the muscle under investigation, but not yet known for facial muscles.

METHODS

Using a figure-of-eight coil, we compared TMS induced motor evoked potentials (MEPs) from eight different coil orientations when recording from ipsi- and contralateral nasalis muscle.

RESULTS

The MEPs from nasalis muscle revealed three components: The major ipsi- and contra-lateral middle latency responses of approximately 10 ms onset latency proved entirely dependent on voluntary pre-innervation. They were most easily obtained from a coil orientation with posterior inducing current direction, and in this respect resembled the intrinsic hand rather than the masseter muscles. Early short duration responses of around 6 ms onset latency were best elicited with an antero-lateral current direction and not pre-innervation dependent, and therefore most probably due to stimulation of the nerve roots. Late responses (>18 ms) could inconsistently be elicited with posterior coil orientations in pre-innervated condition.

CONCLUSIONS

By using the appropriate coil orientation and both conditions relaxed and pre-innervated, cortically evoked MEP responses from nasalis muscle can reliably be separated from peripheral and reflex components and also from cross talk of masseter muscle activation.

Central motor conduction differs between acute relapsing–remitting and chronic progressive multiple sclerosis

OBJECTIVE

To characterize central motor conduction in relation to the clinical deficits and to the disease duration in 90 patients with acute relapsing-remitting MS (RR-MS) and in 51 patients with chronic primary or secondary progressive MS (P-MS).

METHODS

The triple stimulation technique (TST) was used to quantify the central motor conduction failure (expressed by the TST amplitude ratio) and conventional motor evoked potentials (MEPs) were used to measure the central motor conduction time (CMCT).

RESULTS

The TST amplitude ratio was reduced in presence of a clinical motor deficit (p=0.02 for RR-MS, p<0.01 for P-MS), but did not significantly differ in RR-MS and P-MS (p>0.05) when patients with similar clinical motor deficit were compared. The CMCT was not related to the clinical motor deficit in both RR-MS and P-MS. However, the CMCT was markedly prolonged in P-MS, when patients with similar clinical motor deficit and with similar disease duration were compared (p<0.01). The differences were not attributable to differential involvement of the spinal cord, which was similar in RR-MS and P-MS.

CONCLUSIONS

Our results disclose differences between the central motor conduction in RR-MS and P-MS that are not related to disease severity, spinal cord involvement or disease duration.

Abnormal trafficking of sarcolemmal proteins in alpha-glucosidase deficiency

The dystrophin-associated protein complex (DAP) plays an important role in the integrity and stability of the muscle membrane. Whereas much is known about the interaction between DAP members at the sarcolemmal location, intracellular DAP assembly and trafficking is still largely unknown. In alpha-glucosidase (acid maltase) deficiency (alphaGDD), accumulation of glycogen is accompanied by cytoarchitectural abnormalities impairing normal protein metabolism. In the present study, we took advantage of this fact to examine the consequences of impaired protein handling on the formation of DAP, with the aim of gaining indirect knowledge about its sarcoplasmic trafficking and a better understanding of mechanisms leading to myopathic changes found in alphaGDD. Histological examination of alphaGDD muscle confirmed a vacuolar myopathy with glycogen accumulation both in vacuoles and within the sarcoplasm. Sarcoplasmic accumulation of sarcolemmal proteins, including dystrophin and sarcoglycans, occurred around some vacuoles and within non-vacuolated fibres. Utrophin was up-regulated and found at extra-junctional sarcolemmal locations of many fibres. AlphaGDD muscle cells developed in a fashion similar to that of controls in culture. However, vacuoles were found in 2-week-old alphaGDD myotubes, and these subsequently increased in size and number. Substantial alterations in DAP handling were found, with accumulation close to the Golgi apparatus. Utrophin was not enriched in the sarcoplasm but was up-regulated along the whole sarcolemma. Our results demonstrate a close association of dystrophin and sarcoglycans during sarcoplasmic processing. Furthermore, they suggest that the myopathy found in alphaGDD is a secondary form of DAP deficiency.

[Contribution of electrophysiology to the study of a paresis of central origin]

Motor evoked potentials (MEPs) to magnetic transcranial stimulation allow a functional study of the central motor pathways (from cortex to muscle). The method--noninvasive, painless and hazard-free--is readily accepted by the patients. Two main parameters are measured, namely the central motor conduction time (CMCT) and the size of the MEP. The CMCT provides information on the conduction velocity along the corticospinal pathway, it is particularly prolonged in myelin disorders. The size of MEPs correlates with the proportion of functioning motor neurons. A particular technique allows a precise quantification of conduction defects due to conduction blocks or neuronal lesions that are responsible for the paresis. Clinical applications of the method are numerous; mainly, to detect, measure and localize a dysfunction of central motor conduction of any origin. The method serves the diagnosis and on some occasions the prognosis; it allows the follow up of central motor paresis and the effect of treatments.

Effect of discharge desynchronization on the size of motor evoked potentials: an analysis

OBJECTIVE

Motor evoked potentials (MEPs) after transcranial magnetic brain stimulation (TMS) are smaller than CMAPs after peripheral nerve stimulation, because desynchronization of the TMS-induced motor neurone discharges occurs (i.e. MEP desynchronization). This desynchronization effect can be eliminated by use of the triple stimulation technique (TST; Brain 121 (1998) 437). The objective of this paper is to study the effect of discharge desynchronization on MEPs by comparing the size of MEP and TST responses.

METHODS

MEP and TST responses were obtained in 10 healthy subjects during isometric contractions of the abductor digiti minimi, during voluntary background contractions between 0% and 20% of maximal force, and using 3 different stimulus intensities. Additional data from other normals and from multiple sclerosis (MS) patients were obtained from previous studies.

RESULTS

MEPs were smaller than TST responses in all subjects and under all stimulating conditions, confirming the marked influence of desynchronization on MEPs. There was a linear relation between the amplitudes of MEPs vs. TST responses, independent of the degree of voluntary contraction and stimulus intensity. The slope of the regression equation was 0.66 on average, indicating that desynchronization reduced the MEP amplitude on average by one third, with marked inter-individual variations. A similar average proportion was found in MS patients.

CONCLUSIONS

The MEP size reduction induced by desynchronization is not influenced by the intensity of TMS and by the level of facilitatory voluntary background contractions. It is similar in healthy subjects and in MS patients, in whom increased desynchronization of central conduction was previously suggested to occur. Thus, the MEP size reduction observed may not parallel the actual amount of desynchronization.

Effort-induced mirror movements. A study of transcallosal inhibition in humans

During sustained, fatiguing maximal voluntary contraction of muscles of one hand, muscles of the other hand gradually become activated also. Such effort-induced mirror movements indicate a decreased ability of the central nervous system (CNS) to selectively control individual muscles. We studied whether altered transcallosal inhibition (TCI) contributed to this phenomenon. TCI was determined in ten healthy subjects by measuring the ipsilateral silent period (iSP) and the contralateral silent period (cSP) during a sustained contraction of the abductor digiti minimi, induced by focal unihemispheric ipsilateral transcranial magnetic stimulation. Mirror movements occurred in all subjects in response to the effort. There was a bilateral increase in cSPs and a parallel increase in the iSP in the contralateral working muscle. In contrast, the iSP in the mirroring muscle remained unchanged, explained by a balance of increased crossed pyramidal inhibition (cSP) and decreased transcallosal inhibition. In finely tuned unimanual movements, mirroring activity of the contralateral hand is suppressed by TCI originating in the working hemisphere. During sustained, effortful contractions, the outflow of the contralateral hemisphere is increased due to reduced TCI. Effort-induced mirror contractions are thus the result of disinhibition of contralateral crossed projections rather than disinhibition of ipsilateral uncrossed pathways.

Transcranial magnetic brain stimulation: a tool to investigate central motor pathways

Transcranial magnetic stimulation allows the painless activation of cortical motor neurons and elicits responses in a wide range of muscles, termed “motor-evoked potentials.” Since its introduction in 1985, the technique has evolved as one of the most fruitful recent contributions to clinical neurophysiology.

Inhibitory conditioning stimulus in transcranial magnetic stimulation reduces the number of excited spinal motor neurons

OBJECTIVE

To study the mechanisms of amplitude attenuation caused by a transcranial magnetic conditioning stimulus. Both conventional MEPs and the recently described triple stimulation technique (TST) were applied; the latter to improve the quantification of the response size decrease.

METHODS

TST uses a peripheral collision method to eliminate the effects of desynchronization of the transcranial magnetic stimulation (TMS) induced spinal motor neuron discharges. The attenuation of motor evoked potentials (MEPs) and responses to TST was studied in 10 healthy volunteers using the conditioning-test paradigm with 2 ms interstimulus intervals.

RESULTS

Conventional MEPs and responses to TST demonstrated a marked attenuation by the preceding conditioning stimulus in all subjects. The ratio of MEP to TST amplitudes was the same in conditioned and unconditioned responses.

CONCLUSIONS

Our findings suggest that the transcranial conditioning stimulus does not change the degrees of desynchronization of spinal motor neuron discharges, but results in a reduced number of excited alpha motor neurons. This reduction can be estimated by both MEPs and TST.

The triple stimulation technique to study central motor conduction to the lower limbs

OBJECTIVE

To quantify the percentage of motor units of a foot muscle that can be activated by transcranial magnetic stimulation (TMS) in normal subjects and patients.

METHODS

We adapted the recently described triple stimulation technique (TST) for recordings from abductor hallucis (AH). Conventional motor evoked potentials (MEPs) of this muscle are usually small and variable in shape, because of an important temporal desynchronization of the TMS induced spinal motor neuron discharges. The TST allows 'resynchronization' of these discharges and thereby a quantification of the proportion of motor units activated by TMS. The lower limb (LL-) TST was applied to 33 sides of 18 normal subjects and 51 sides of 46 patients with multiple sclerosis, amyotrophic lateral sclerosis, or spinal cord disorders.

RESULTS

In healthy subjects, the LL-TST demonstrated that TMS achieves activation of virtually all motor neurons supplying the AH. In 33 of 51 patient sides, abnormal LL-TST responses suggested corticospinal conduction failures of various degrees. The LL-TST was 2.54 times more sensitive to detect central conduction failures than the conventional LL-MEPs. Combining the LL-TST with TST of the upper limbs further increased the sensitivity to detect a conduction failure by 1.50 times.

CONCLUSION

The LL-TST markedly improves the examination of corticospinal pathways.

Quantification of upper motor neuron loss in amyotrophic lateral sclerosis

OBJECTIVE

To quantitatively estimate upper motor neuron (UMN) loss in ALS.

METHODS

We used the recently developed triple stimulation technique (TST) to study corticospinal conduction to 86 abductor digiti minimi muscles of 48 ALS patients. This method employs a collision technique to estimate the proportion of motor units activated by a transcranial magnetic stimulus. At the same time, it yields an estimate of lower motor neuron (LMN) integrity.

RESULTS

The TST disclosed and quantified central conduction failures attributable to UMN loss in 38 sides of 24 patients (subclinical in 15 sides), whereas conventional motor evoked potentials detected abnormalities in only 18 sides of 12 patients (subclinical in two sides). The increased sensitivity of the TST to detect UMN dysfunction was particularly observed in early cases. Increased central motor conduction times (CMCT) occurred exclusively in sides with conduction failure. In sides with clinical UMN syndromes, the TST response size (but not the CMCT) correlated with the muscle weakness. In sides with clinical LMN syndromes, the size of the peripherally evoked compound muscle action potentials correlated with the muscle weakness.

CONCLUSION

The TST is a sensitive method to detect UMN dysfunction in ALS. It allows a quantitative estimate of the UMN loss, which is related to the functional deficit. Therefore, the TST has a considerable impact on diagnostic certainty in many patients. It will be suited to follow the disease progression and therapeutic trials.

Polyneuropathy attributes: a comparison between patients with anti-MAG and anti-sulfatide antibodies

Thirty-two patients with a peripheral neuropathy and paraproteinemia were tested for IgM antibodies against myelin-associated protein (MAG) and sulfatide by means of enzyme-linked immunosorbent assay. Nine patients (28 %) had increased anti-sulfatide IgM antibodies and showed a chronic, slowly progressive, distally pronounced, and symmetric polyneuropathy with sensory to sensory-motor impairment, ataxia, hyporeflexia, and axonal involvement in electrophysiological studies. Ten patients (31 %) with increased anti-MAG antibodies had a similar, homogeneous polyneuropathy syndrome but presented with demyelinating features. A weak cross-reactivity between anti-MAG and anti-sulfatide antibodies was present in only three patients. In conclusion, although the two neuropathy groups clearly differed in their electrophysiological features, their clinical presentation was rather similar.

Intraoperative electromyography of the superior gluteal nerve during lateral approach to the hip for arthroplasty: a prospective study of 12 patients

The purpose of this study was to evaluate the incidence of intraoperative superior gluteal nerve irritation and to identify specific surgical maneuvers that may harm the nerve. Continuous intraoperative electromyography (EMG) monitoring of the superior gluteal nerve-innervated muscles (gluteus medius and tensor fascia lata muscles) was performed in 12 patients undergoing total hip arthroplasty. A modified lateral approach was used, including a partial anterior osteotomy of the greater trochanter with splitting of the gluteus medius and vastus lateralis muscles. All patients had a clinical follow-up examination 1 year postoperatively to evaluate abductor muscle function. Irritation of the nerve occurred first during splitting of the gluteus medius muscle, then with increased gluteus medius retraction for exposure of the acetabulum, and finally during positioning of the leg for preparation of the femur. The detected EMG alterations were important because they were found in a single patient with persistent abductor muscle weakness.

Amyotrophic lateral sclerosis versus cervical spondylotic myelopathy: a study using transcranial magnetic stimulation with recordings from the trapezius and limb muscles

OBJECTIVE

We report an electrophysiological method to differentiate amyotrophic lateral sclerosis (ALS) from cervical spondylotic myelopathy (CSM).

METHODS

Motor evoked potentials (MEPs) by transcranial magnetic stimulation were investigated in patients with ALS (n=10) and CSM (n=9). In addition to limb MEPs using the triple stimulation technique (TST) at upper limbs, MEPs recorded from trapezius muscles were compared with those obtained from 23 normal subjects. The parameters studied were: central motor conduction time, amplitude ratio and, for the trapezius, the interside asymmetry.

RESULTS

Whereas limb MEPs were abnormal in most ALS and CSM patients (17/19), trapezius MEPs were abnormal in all ALS patients, and normal in 8 out of 9 CSM patients.

CONCLUSION

Recording of trapezius MEPs is a valuable addition to the limb MEPs study, since it distinguishes ALS from SCM in most patients.

Facial nerve dysfunction in hereditary motor and sensory neuropathy type I and III

Facial nerve function was studied in 19 patients with hereditary motor and sensory neuropathy type I (HMSN I) and 2 patients with hereditary motor and sensory neuropathy type III (HMSN III, Déjérine-Sottas), and compared to that in 24 patients with Guillain-Barré syndrome (GBS). The facial nerve was stimulated electrically at the stylomastoid fossa, and magnetically in its proximal intracanalicular segment. Additionally, the face-associated motor cortex was stimulated magnetically. The facial nerve motor neurography was abnormal in 17 of 19 HMSN I patients and in both HMSN III patients, revealing moderate to marked conduction slowing in both the extracranial and intracranial nerve segments, along with variable reductions of compound muscle action potential (CMAP) amplitudes. The facial nerve conduction slowing paralleled that of limb nerves, but was not associated with clinical dysfunction of facial muscles, because none of the HMSN I patients had facial palsy. Conduction slowing was most severe in the HMSN III patients, but only slight facial weakness was present. In GBS, conduction slowing was less marked, but facial weakness exceeded that in HMSN patients in all cases. We conclude that involvement of the facial nerve is common in HMSN I and HMSN III. It affects the intra- and extracranial part of the facial nerve and is mostly subclinical.

Nonspecific facilitation of responses to transcranial magnetic stimulation

We examined the effect of facial muscle contraction and eye movements on motor evoked potentials (MEPs) from the abductor pollicis brevis muscle (APB) evoked by transcranial magnetic stimulation (TMS). The hypothesis was that activity of large cortical regions (face) influences the excitability of spinal motoneurons via cortical or subcortical pathways. MEPs were recorded in 12 healthy subjects during the following conditions: (1) rest; (2) facial muscle contraction; (3) eye movements; (4) 10% precontraction of the target muscle; and (5) simultaneous target muscle precontraction and facial muscle contraction. In 9 subjects, spinal motoneuron excitability was assessed by measurements of F waves during the same facilitation maneuvers. Activation of eye and facial muscles clearly facilitated MEPs from the APB. The facilitation of MEP size during nonspecific maneuvers was almost similar to that obtained by target muscle precontraction, whereas shortening of latencies was significantly smaller. The occurrence and amplitude of F waves increased in parallel with MEP size during specific and nonspecific facilitation, pointing to spinal motoneuronal threshold changes as a potential facilitatory mechanism by facial and eye muscle activation. The different MEP latencies during specific and nonspecific facilitation were not explained by different spinal motoneuron excitability, but raise the possibility that supraspinal mechanisms contributed to nonspecific facilitation.

[Progressive muscular weakness due to subacute postinfectious polyradiculitis and myelitis]

In a 67-year-old patient, generalised stable muscular weakness preexisting for several years became rapidly progressive within a few weeks prior to hospitalisation. He died one month after admission from acute cardiocirculatory failure. There was no history of muscular pain, clinical examination showed weak or absent tendon reflexes, hyposensibility of the dorsa of his feet, fasciculations and myocloni of the muscles of the lower limbs as well as a generalised muscular atrophy. Polyneuropathy due to diabetes mellitus and monoclonal IGG-kappa-type gammopathy were preexisting. CSF examination showed inflammatory cerebral fluid changes and further investigations revealed inflammatory polyradiculopathy affecting mainly motor nerve fibres. There was evidence of a reactivated varicella-zoster infection in serum and in the cerebrospinal fluid samples. The search for a tumour, vasculitis or a drug-related cause for this syndrome remained negative. Neuropathological examination at autopsy showed subacute polyradiculitis accompanied by myelitis. The most probable cause of this disorder is immune-mediated polyradiculitis after varicella-zoster infection.

Rapid cortical motor output map changes assessed by the triple stimulation technique

The amplitudes of motor evoked potentials (MEPs) were mapped by transcranial magnetic stimulation (TMS) using the triple stimulation technique (TST) in 11 normal individuals. Stimuli were given while the subjects were (a) distracted, (b) concentrating on their target (recorded) hand, and (c) concentrating on their contralateral hand. Within seconds, the proportion of excited motor units increased, similarly in all subjects, by an average of 70% from (a) to (b), and by 48% from (a) to (c). At the optimal stimulation site, results obtained with the TST were compared to those of conventional MEPs. The TST proved superior in detecting the rapid changes of the motor output caused by the non-specific mental tasks studied.