Abnormal sensory evoked potentials in amyotrophic lateral sclerosis

Non-motor symptoms in patients with amyotrophic lateral sclerosis: current state and future directions

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive degeneration of both upper and lower motor neurons. A defining histopathological feature in approximately 97% of all ALS cases is the accumulation of phosphorylated trans-activation response (TAR) DNA-binding protein 43 protein (pTDP-43) aggregates in the cytoplasm of neurons and glial cells within the central nervous system. Traditionally, it was believed that the accumulation of TDP-43 aggregates and subsequent neurodegeneration primarily occurs in motor neurons. However, contemporary evidence suggests that as the disease progresses, other systems and brain regions are also affected. Despite this, there has been a limited number of clinical studies assessing the non-motor symptoms in ALS patients. These studies often employ various outcome measures, resulting in a wide range of reported frequencies of non-motor symptoms in ALS patients. The importance of assessing the non-motor symptoms reflects in a fact that they have a significant impact on patients' quality of life, yet they frequently go underdiagnosed and unreported during clinical evaluations. This review aims to provide an up-to-date overview of the current knowledge concerning non-motor symptoms in ALS. Furthermore, we address their diagnosis and treatment in everyday clinical practice.

Multimodal MRI improves diagnostic accuracy and sensitivity to longitudinal change in amyotrophic lateral sclerosis

BACKGROUND

Recent advances in MRI acquisitions and image analysis have increased the utility of neuroimaging in understanding disease-related changes. In this work, we aim to demonstrate increased sensitivity to disease progression as well as improved diagnostic accuracy in Amyotrophic lateral sclerosis (ALS) with multimodal MRI of the brain and cervical spinal cord.

METHODS

We acquired diffusion MRI data from the brain and cervical cord, and T1 data from the brain, of 20 participants with ALS and 20 healthy control participants. Ten ALS and 14 control participants, and 11 ALS and 13 control participants were re-scanned at 6-month and 12-month follow-ups respectively. We estimated cross-sectional differences and longitudinal changes in diffusion metrics, cortical thickness, and fixel-based microstructure measures, i.e. fiber density and fiber cross-section.

RESULTS

We demonstrate improved disease diagnostic accuracy and sensitivity through multimodal analysis of brain and spinal cord metrics. The brain metrics also distinguished lower motor neuron-predominant ALS participants from control participants. Fiber density and cross-section provided the greatest sensitivity to longitudinal change. We demonstrate evidence of progression in a cohort of 11 participants with slowly progressive ALS, including in participants with very slow change in ALSFRS-R. More importantly, we demonstrate that longitudinal change is detectable at a six-month follow-up visit. We also report correlations between ALSFRS-R and the fiber density and cross-section metrics.

CONCLUSIONS

Our findings suggest that multimodal MRI is useful in improving disease diagnosis, and fixel-based measures may serve as potential biomarkers of disease progression in ALS clinical trials.

Tibial nerve SEPs in diagnosing lumbar spinal stenosis: The utility of segmental evaluation using P15 and N21

Objective

To establish the utility of the additional evaluation of the P15 potential generated at the greater sciatic foramen in the tibial nerve somatosensory evoked potentials (SEPs) in diagnosing lumbar spinal stenosis (LSS).

Methods

We retrospectively reviewed tibial nerve SEP findings in patients having MRI-confirmed LSS at the cauda equina or conus/epiconus region. P15 and N21 potentials were recorded and the following findings were defined as localizing abnormalities: 1) normal P15 latency either with prolonged P15-N21 interval or with absent N21; 2) decreased ratio of the N21 amplitude to P15 amplitude. As non-localizing abnormalities, N21 and P38 latencies were also evaluated. Tibial nerve F-wave findings were also investigated.

Results

According to the entry criteria, 18 patients were included, 15 with cauda equina lesions and 3 with conus/epiconus lesions. Localizing abnormalities in SEPs were found in 67% of patients, achieving significantly higher sensitivity than delayed P38 latency (28%), and higher sensitivity than N21 abnormalities (39%), though this was not significant. Localizing abnormalities were observed even in 6 out of 11 patients lacking both sensory symptoms and signs. Tibial nerve F-wave was abnormal in 36% of 14 patients with F-wave examinations, whereas the localizing abnormalities in SEPs were found in 64% of the same patient population. P15 amplitude was depressed in 4 patients (22%), which may indicate the involvement of the dorsal root ganglion in LSS, although its latency was normal even for these patients.

Conclusions

Tibial nerve SEPs with the recording of P15 and N21 potentials achieved sufficiently high sensitivity in diagnosing LSS. They have the advantage over F-wave in that they can localize the lesion at the cauda equina or conus/epiconus level.

Significance

Tibial nerve SEPs are promising in evaluating LSS, especially in documenting sensory tract involvement in cases lacking sensory symptoms/signs.

Sensory Involvement in Amyotrophic Lateral Sclerosis

Although amyotrophic lateral sclerosis (ALS) is pre-eminently a motor disease, the existence of non-motor manifestations, including sensory involvement, has been described in the last few years. Although from a clinical perspective, sensory symptoms are overshadowed by their motor manifestations, this does not mean that their pathological significance is not relevant. In this review, we have made an extensive description of the involvement of sensory and autonomic systems described to date in ALS, from clinical, neurophysiological, neuroimaging, neuropathological, functional, and molecular perspectives.

Reduced Occipital Cortex Excitability in Amyotrophic Lateral Sclerosis

PURPOSE

In addition to motor cortex involvement, sensory abnormalities have been demonstrated in amyotrophic lateral sclerosis (ALS), including structural and metabolic alterations in the occipital cortex. The aim of this study was to examine occipital excitability changes in ALS.

METHODS

Twenty-one patients with ALS and 16 healthy subjects were enrolled into the study. Phosphene experience and phosphene threshold were studied to assess occipital excitability. Cognitive function was evaluated in both groups by means of Montreal Cognitive Assessment and Addenbrooke's Cognitive Examination-Revised visuospatial score tests.

RESULTS

Phosphene was experienced in 13 (81.3%) healthy subjects and 9 (42.9%) patients with ALS (P = 0.04). The mean phosphene threshold was not significantly different between the two groups. No correlation existed between phosphene threshold and motor cortical excitability parameters, ALS Functional Rating Scale Revised, Montreal Cognitive Assessment, and Addenbrooke's Cognitive Examination-Revised scores.

CONCLUSIONS

Visual cortex is affected, and the occipital excitability is reduced in ALS, without any relation to motor cortical excitability changes, providing another clue suggestive of sensory involvement in ALS.

Clinical and preclinical evidence of somatosensory involvement in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron neurodegenerative disease. Although it has been classically considered as a disease limited to the motor system, there is increasing evidence for the involvement of other neural and non-neuronal systems. In this review, we will discuss currently existing literature regarding the involvement of the sensory system in ALS. Human studies have reported intradermic small fibre loss, sensory axonal predominant neuropathy, as well as somatosensory cortex hyperexcitability. In line with this, ALS animal studies have demonstrated the involvement of several sensory components. Specifically, they have highlighted the impairment of sensory-motor networks as a potential mechanism for the disease. The elucidation of these "non-motor" systems involvement, which might also be part of the degeneration process, should prompt the scientific community to re-consider ALS as a pure motor neuron disease, which may in turn result in more holistic research approaches. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Tract-specific analysis improves sensitivity of spinal cord diffusion MRI to cross-sectional and longitudinal changes in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset fatal neurodegenerative disease that causes progressive degeneration of motor neurons in the brain and the spinal cord. Corticospinal tract degeneration is a defining feature of ALS. However, there have been very few longitudinal, controlled studies assessing diffusion MRI (dMRI) metrics in different fiber tracts along the spinal cord in general or the corticospinal tract in particular. Here we demonstrate that a tract-specific analysis, with segmentation of ascending and descending tracts in the spinal cord white matter, substantially increases the sensitivity of dMRI to disease-related changes in ALS. Our work also identifies the tracts and spinal levels affected in ALS, supporting electrophysiologic and pathologic evidence of involvement of sensory pathways in ALS. We note changes in diffusion metrics and cord cross-sectional area, with enhanced sensitivity to disease effects through a multimodal analysis, and with strong correlations between these metrics and spinal components of ALSFRS-R.

Interrogating interneurone function using threshold tracking of the H reflex in healthy subjects and patients with motor neurone disease

OBJECTIVE

The excitability of the lower motoneurone pool is traditionally tested using the H reflex and a constant-stimulus paradigm, which measures changes in the amplitude of the reflex response. This technique has limitations because reflex responses of different size must involve the recruitment or inhibition of different motoneurones. The threshold-tracking technique ensures that the changes in excitability occur for an identical population of motoneurones. We aimed to assess this technique and then apply it in patients with motor neurone disease (MND).

METHODS

The threshold-tracking approach was assessed in 17 healthy subjects and 11 patients with MND. The soleus H reflex was conditioned by deep peroneal nerve stimulation producing reciprocal Ia and so-called D1 and D2 inhibitions, which are believed to reflect presynaptic inhibition of soleus Ia afferents.

RESULTS

Threshold tracking was quicker than the constant-stimulus technique and reliable, properties that may be advantageous for clinical studies. D1 inhibition was significantly reduced in patients with MND.

CONCLUSIONS

Threshold tracking is useful and may be preferable under some conditions for studying the excitability of the motoneurone pool. The decreased D1 inhibition in the patients suggests that presynaptic inhibition may be reduced in MND.

SIGNIFICANCE

Reduced presynaptic inhibition could be evidence of an interneuronopathy in MND. It is possible that the hyperreflexia is a spinal pre-motoneuronal disorder, and not definitive evidence of corticospinal involvement in MND.

Changes in Retinal OCT and Their Correlations with Neurological Disability in Early ALS Patients, a Follow-Up Study

BACKGROUND

To compare early visual changes in amyotrophic lateral sclerosis (ALS) patients with healthy controls in a baseline exploration, to follow-up the patients after 6 months, and to correlate these visual changes with neurological disability.

METHODS

All patients underwent a comprehensive neurological and ophthalmological examination. A linear mixed analysis and Bonferroni p-value correction were performed, testing four comparisons as follows: Control baseline vs. control follow-up, control baseline vs. ALS baseline, control follow-up vs. ALS follow-up, and ALS baseline vs. ALS follow-up.

RESULTS

The mean time from the diagnosis was 10.80 ± 5.5 months. The analysis of the optical coherence tomography (OCT) showed: (1) In ALS baseline vs. control baseline, a macular significantly increased thickness of the inner macular ring temporal and inferior areas; (2) in ALS follow-up vs. ALS baseline, a significant macular thinning in the inner and outer macular ring inferior areas; (3) in ALS follow-up vs. ALS baseline, a significant peripapillary retinal nerve fiber layer (pRNFL) thinning in the superior and inferior quadrants; and (4) ALS patients showed a moderate correlation between some OCT pRNFL parameters and Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) score.

CONCLUSION

The OCT showed retinal changes in patients with motoneuron disease and could serve as a complementary tool for studying ALS.

Excitability in somatosensory cortex correlates with motoric impairment in amyotrophic lateral sclerosis

Objective: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative motoneuron disease. As previous studies reported alterations in motor cortex excitability, we evaluate excitability changes in somatosensory system. Methods: We examined 15 ALS patients and 15 healthy controls. Cortical excitability was assessed using paired somatosensory evoked potentials of median nerves. To determine disease severity and functional impairment, we assessed muscle strength and revised ALS-Functional Rating Scale (ALSFRS-R). Results: We found significantly reduced bilateral paired-stimulation inhibition in the ALS-group (both p < 0.05). Additionally, paired-stimulation ratios significantly correlated with ALSFRS-R (left somatosensory cortex: r= -orte; right somatosensory cortex: r= -ort4; both p < 0.05) and contralateral muscle strength (left somatosensory cortex: r= -orte, p = 0.007; right somatosensory cortex: r= -ortex p = 0.003). Conclusions: The results indicate disinhibition of the somatosensory cortex in ALS. It remains open if central somatosensory disinhibition is a primary characteristic of ALS as one element of a multisystem neurodegenerative disorder or a compensatory up-regulation due to functional motoric impairment. Longitudinal studies are necessary to categorize these findings.

Imaging Cerebral Activity in Amyotrophic Lateral Sclerosis

Advances in neuroimaging, complementing histopathological insights, have established a multi-system involvement of cerebral networks beyond the traditional neuromuscular pathological view of amyotrophic lateral sclerosis (ALS). The development of effective disease-modifying therapy remains a priority and this will be facilitated by improved biomarkers of motor system integrity against which to assess the efficacy of candidate drugs. Functional MRI (FMRI) is an established measure of both cerebral activity and connectivity, but there is an increasing recognition of neuronal oscillations in facilitating long-distance communication across the cortical surface. Such dynamic synchronization vastly expands the connectivity foundations defined by traditional neuronal architecture. This review considers the unique pathogenic insights afforded by the capture of cerebral disease activity in ALS using FMRI and encephalography.

Electrophysiological correlates of neurodegeneration in motor and non-motor brain regions in amyotrophic lateral sclerosis-implications for brain-computer interfacing

OBJECTIVE

For patients with amyotrophic lateral sclerosis (ALS) who are suffering from severe communication or motor problems, brain-computer interfaces (BCIs) can improve the quality of life and patient autonomy. However, current BCI systems are not as widely used as their potential and patient demand would let assume. This underutilization is a result of technological as well as user-based limitations but also of the comparatively poor performance of currently existing BCIs in patients with late-stage ALS, particularly in the locked-in state.

APPROACH

Here we review a broad range of electrophysiological studies in ALS patients with the aim to identify electrophysiological correlates of ALS-related neurodegeneration in motor and non-motor brain regions in to better understand potential neurophysiological limitations of current BCI systems for ALS patients. To this end we analyze studies in ALS patients that investigated basic sensory evoked potentials, resting-state and task-based paradigms using electroencephalography or electrocorticography for basic research purposes as well as for brain-computer interfacing. Main results and significance. Our review underscores that, similarly to mounting evidence from neuroimaging and neuropathology, electrophysiological measures too indicate neurodegeneration in non-motor areas in ALS. Furthermore, we identify an unexpected gap of basic and advanced electrophysiological studies in late-stage ALS patients, particularly in the locked-in state. We propose a research strategy on how to fill this gap in order to improve the design and performance of future BCI systems for this patient group.

Excitability of sensory axons in amyotrophic lateral sclerosis

OBJECTIVE

To evaluate the excitability of sensory axons in patients with amyotrophic lateral sclerosis (ALS).

METHODS

Comprehensive sensory nerve excitability studies were prospectively performed on 28 sporadic ALS patients, compared to age-matched controls. Sensory nerve action potentials were recorded from digit 2 following median nerve stimulation at the wrist. Disease severity was measured using motor unit number estimation (MUNE), the revised ALS Functional Rating Scale (ALSFRS-R) and the MRC scale.

RESULTS

There were no significant differences in standard and extended measures of nerve excitability between ALS patients and controls. These unchanged excitability measures included accommodation to long-lasting hyperpolarization and the threshold changes after two supramaximal stimuli during the recovery cycle. Excitability parameters did not correlate with MUNE, ALSFRS-R, APB MRC scale or disease duration.

CONCLUSIONS

This cross-sectional study has identified normal axonal membrane properties in myelinated sensory axons of ALS patients. Previously described sensory abnormalities could be the result of axonal fallout, possibly due to a ganglionopathy, or to involvement of central sensory pathways rostral to gracile and cuneate nuclei.

SIGNIFICANCE

These results demonstrate the absence of generalized dysfunction of the membrane properties of sensory axons in ALS in the face of substantial deficits in motor function.

Sensory cortex hyperexcitability predicts short survival in amyotrophic lateral sclerosis

OBJECTIVE

To investigate somatosensory cortex excitability and its relationship to survival prognosis in patients with amyotrophic lateral sclerosis (ALS).

METHODS

A total of 145 patients with sporadic ALS and 73 healthy control participants were studied. We recorded compound muscle action potential and sensory nerve action potential of the median nerve and the median nerve somatosensory evoked potential (SEP), and we measured parameters, including onset-to-peak amplitude of N13 and N20 and peak-to-peak amplitude between N20 and P25 (N20p-P25p). Clinical prognostic factors, including ALS Functional Rating Scale-Revised, were evaluated. We followed up patients until the endpoints (death or tracheostomy) and analyzed factors associated with survival using multivariate analysis in the Cox proportional hazard model.

RESULTS

Compared to controls, patients with ALS showed a larger amplitude of N20p-P25p in the median nerve SEP. Median survival time after examination was shorter in patients with N20p-P25p ≥8 μV (0.82 years) than in those with N20p-P25p <8 μV (1.68 years, p = 0.0002, log-rank test). Multivariate analysis identified a larger N20p-P25p amplitude as a factor that was independently associated with shorter survival (p = 0.002).

CONCLUSION

Sensory cortex hyperexcitability predicts short survival in patients with ALS.

Motor neurone disease

Motor neurone disease (MND) patients exhibit poor gait, balance, and postural control, all of which significantly increases their risk of falling. Falls are frequent in the MND population, and are associated with an increased burden of disease. The complex interplay of both motor and extramotor manifestations in this disease contributes to the heterogeneous and multifactorial causes of such dysfunction. This review highlights the pathophysiologic influence of motor degeneration in gait disturbance, but also the additional influence on postural instability from other inputs such as cognitive impairment, autonomic dysregulation, cerebellar dysfunction, sensory impairment, and extrapyramidal involvement. In various combinations, these impairments are responsible for reduced gait speed and alteration in gait cycle, as well as structurally more variable and disorganized gait patterns. Based on these features, this chapter will also provide disease-specific interventions to assess, manage, and prevent falls in the MND cohort.

Abnormal cortical brain integration of somatosensory afferents in ALS

OBJECTIVES

Infraclinical sensory alterations have been reported at early stages of amyotrophic lateral sclerosis (ALS). While previous studies mainly focused on early somatosensory evoked potentials (SEPs), late SEPs, which reflect on cortical pathways involved in cognitive-motor functions, are relatively underinvestigated. Early and late SEPs were compared to assess their alterations in ALS.

METHODS

Median and ulnar nerves were electrically stimulated at the wrist, at 9 times the perceptual threshold, in 21 ALS patients without clinical evidence of sensory deficits, and 21 age- and gender-matched controls. SEPs were recorded at the Erb point using surface electrodes and using a needle inserted in the scalp, in front of the primary somatosensory area (with reference electrode on the ear lobe).

RESULTS

Compared to controls, ALS patients showed comparable peripheral (N9) and early cortical component (N20, P25, N30) reductions, while the late cortical components (N60, P100) were more depressed than the early ones.

CONCLUSIONS

The peripheral sensory alteration likely contributed to late SEP depression to a lesser extent than that of early SEPs.

SIGNIFICANCE

Late SEPs may provide new insights on abnormal cortical excitability affecting brain areas involved in cognitive-motor functions.

Extra-motor abnormalities in amyotrophic lateral sclerosis: another layer of heterogeneity

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease defined by the presence of muscle weakness. The motor features of disease are heterogeneous in site of onset and progression. There are also extra-motor features in some patients. The genetic basis for extra-motor features is uncertain. The heterogeneity of ALS is an issue for clinical trials. Areas covered: This paper reviews the range and prevalence of extra-motor features associated with ALS, and highlights the current information about genetic associations with extra-motor features. Expert commentary: There are extra-motor features of ALS, but these are not found in all patients. The most common is cognitive abnormality. More data is required to ascertain whether extra-motor features arise with progression of disease. Extra-motor features are reported in patients with a range of causative genetic mutations, but are not found in all patients with these mutations. Further studies are required of the heterogeneity of ALS, and genotype/phenotype correlations are required, taking note of extra-motor features.

Electrophysiological and spinal imaging evidences for sensory dysfunction in amyotrophic lateral sclerosis

OBJECTIVES

The prevalence of sensory impairment at an early stage of amyotrophic lateral sclerosis (ALS) is still debated. The study aim was to investigate the anatomofunctional properties of sensory pathways in patients with ALS, combining spinal diffusion tensor imaging (DTI) and somatosensory evoked potentials (SEPs).

DESIGN

Case-control study.

SETTINGS

ALS referral centre and laboratory of biomedical imaging (Paris, France).

PARTICIPANTS

Well-characterised group of 21 patients with ALS with moderate disability (mean amyotrophic lateral sclerosis Functional Rating Scale (ALSFRS) score 39.3±1.0) and no clinical sensory signs and control group of 21 gender and age-matched healthy subjects.

OUTCOME MEASURES

Fractional anisotropy and diffusivity of the dorsal columns at C5-T1 levels (DTI metrics) and SEPs after median and ulnar nerve stimulations (latency and amplitude of N9 and N20 components).

RESULTS

Abnormal DTI metrics indicated anatomical damages of ascending sensory fibres in ∼60% of patients (p<0.05). Raw SEPs (μV) were smaller in ∼40% of patients but the difference with healthy subjects was not significant (p>0.16). Their normalisation to prestimulus activity strengthened the difference between groups (p<0.05) and allowed identification of ∼60% of patients with abnormal values. According to N9 latency, the peripheral conduction time was normal in patients (p>0.32) but based on N20 latency, the central conduction time (between spinal cord and parietal cortex) was found to be slower (p<0.05). Significant correlation was found between DTI metrics and N9 amplitude (p<0.05). Altered SEPs were also correlated with the disease duration (p<0.05). Taken together, spinal imaging and electrophysiology helped to identify ∼85% of patients with subclinical sensory defect while separated methods revealed abnormal values in ∼60%.

CONCLUSIONS

Sensory impairments have been underestimated at early stages of ALS. These results show for the first time the interest to combine electrophysiology and imaging to assess non-motor system involvement in ALS.

TRIAL REGISTRATION NUMBER

IDRCB2012-A00016-37.

Assessing attention and cognitive function in completely locked-in state with event-related brain potentials and epidural electrocorticography

OBJECTIVE

Patients in the completely locked-in state (CLIS), due to, for example, amyotrophic lateral sclerosis (ALS), no longer possess voluntary muscle control. Assessing attention and cognitive function in these patients during the course of the disease is a challenging but essential task for both nursing staff and physicians.

APPROACH

An electrophysiological cognition test battery, including auditory and semantic stimuli, was applied in a late-stage ALS patient at four different time points during a six-month epidural electrocorticography (ECoG) recording period. Event-related cortical potentials (ERP), together with changes in the ECoG signal spectrum, were recorded via 128 channels that partially covered the left frontal, temporal and parietal cortex.

MAIN RESULTS

Auditory but not semantic stimuli induced significant and reproducible ERP projecting to specific temporal and parietal cortical areas. N1/P2 responses could be detected throughout the whole study period. The highest P3 ERP was measured immediately after the patient's last communication through voluntary muscle control, which was paralleled by low theta and high gamma spectral power. Three months after the patient's last communication, i.e., in the CLIS, P3 responses could no longer be detected. At the same time, increased activity in low-frequency bands and a sharp drop of gamma spectral power were recorded.

SIGNIFICANCE

Cortical electrophysiological measures indicate at least partially intact attention and cognitive function during sparse volitional motor control for communication. Although the P3 ERP and frequency-specific changes in the ECoG spectrum may serve as indicators for CLIS, a close-meshed monitoring will be required to define the exact time point of the transition.

Stages of pTDP-43 pathology in amyotrophic lateral sclerosis

OBJECTIVE

To see whether the distribution patterns of phosphorylated 43kDa TAR DNA-binding protein (pTDP-43) intraneuronal inclusions in amyotrophic lateral sclerosis (ALS) permit recognition of neuropathological stages.

METHODS

pTDP-43 immunohistochemistry was performed on 70 μm sections from ALS autopsy cases (N = 76) classified by clinical phenotype and genetic background.

RESULTS

ALS cases with the lowest burden of pTDP-43 pathology were characterized by lesions in the agranular motor cortex, brainstem motor nuclei of cranial nerves V, VII, and X-XII, and spinal cord α-motoneurons (stage 1). Increasing burdens of pathology showed involvement of the prefrontal neocortex (middle frontal gyrus), brainstem reticular formation, precerebellar nuclei, and the red nucleus (stage 2). In stage 3, pTDP-43 pathology involved the prefrontal (gyrus rectus and orbital gyri) and then postcentral neocortex and striatum. Cases with the greatest burden of pTDP-43 lesions showed pTDP-43 inclusions in anteromedial portions of the temporal lobe, including the hippocampus (stage 4). At all stages, these lesions were accompanied by pTDP-43 oligodendroglial aggregates. Ten cases with C9orf72 repeat expansion displayed the same sequential spreading pattern as nonexpansion cases but a greater regional burden of lesions, indicating a more fulminant dissemination of pTDP-43 pathology.

INTERPRETATION

pTDP-43 pathology in ALS possibly disseminates in a sequential pattern that permits recognition of 4 neuropathological stages consistent with the hypothesis that pTDP-43 pathology is propagated along axonal pathways. Moreover, the finding that pTDP-43 pathology develops in the prefrontal cortex as part of an ongoing disease process could account for the development of executive cognitive deficits in ALS.

Optical coherence tomography does not support optic nerve involvement in amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

In recent years a possible non-motor involvement of the nervous system in amyotrophic lateral sclerosis (ALS) has come into the focus of research and has been investigated by numerous techniques. Optical coherence tomography (OCT) - with its potential to reveal neuroaxonal retinal damage - may be an appropriate tool to investigate whether the anterior visual pathway is involved. Our aim was to determine whether OCT-based measures of retinal nerve fiber layer, ganglion cell layer, inner nuclear layer and outer nuclear layer thickness are abnormal in ALS, or correlated with disease severity.

METHODS

Seventy-six ALS patients (144 eyes) and 54 healthy controls (108 eyes; HCs) were examined with OCT, including automated intraretinal macular segmentation. ALS disease severity was determined with the Amyotrophic Lateral Sclerosis Functional Rating Scale - Revised.

RESULTS

There was no significant difference between ALS patients and HCs in any of the examined OCT measures. Moreover, OCT parameters showed no correlation with clinical measures of disease severity.

CONCLUSIONS

These findings indicate that involvement of the anterior visual pathway is not one of the non-motor manifestations of ALS.

Patterns of spontaneous brain activity in amyotrophic lateral sclerosis: a resting-state FMRI study

By detecting spontaneous low-frequency fluctuations (LFF) of blood oxygen level–dependent (BOLD) signals, resting-state functional magnetic resonance imaging (rfMRI) measurements are believed to reflect spontaneous cerebral neural activity. Previous fMRI studies were focused on the examination of motor-related areas and little is known about the functional changes in the extra-motor areas in amyotrophic lateral sclerosis (ALS) patients. The aim of this study is to investigate functional cerebral abnormalities in ALS patients on a whole brain scale. Twenty ALS patients and twenty age- and sex-matched healthy volunteers were enrolled. Voxel-based analysis was used to characterize the alteration of amplitude of low frequency fluctuation (ALFF). Compared with the controls, the ALS patients showed significantly decreased ALFF in the visual cortex, fusiform gyri and right postcentral gyrus; and significantly increased ALFF in the left medial frontal gyrus, and in right inferior frontal areas after grey matter (GM) correction. Taking GM volume as covariates, the ALFF results were approximately consistent with those without GM correction. In addition, ALFF value in left medial frontal gyrus was negatively correlated with the rate of disease progression and duration. Decreased functional activity observed in the present study indicates the underlying deficits of the sensory processing system in ALS. Increased functional activity points to a compensatory mechanism. Our findings suggest that ALS is a multisystem disease other than merely motor dysfunction and provide evidence that alterations of ALFF in the frontal areas may be a special marker of ALS.

Involvement of spinal sensory pathway in ALS and specificity of cord atrophy to lower motor neuron degeneration

Our objective was to demonstrate that ALS patients have sensory pathway involvement and that local cord atrophy reflects segmental lower motor neuron involvement. Twenty-nine ALS patients with spinal onset and twenty-one healthy controls were recruited. Diffusion tensor imaging (DTI), magnetization transfer and atrophy index were measured in the spinal cord, complemented with transcranial magnetic stimulations. Metrics were quantified within the lateral corticospinal and the dorsal segments of the cervical cord. Significant differences were detected between patients and controls for DTI and magnetization transfer metrics in the lateral and dorsal segments of the spinal cord. Fractional anisotropy correlated with ALSFRS-R (p = 0.04) and motor threshold (p = 0.02). Stepwise linear regression detected local spinal cord atrophy associated with weakness in the corresponding muscle territory, i.e. C4 level for deltoid and C7 level for hand muscles. In conclusion, impairment of spinal sensory pathways was detected at an early stage of the disease. Our data also demonstrate an association between muscle deficits and local spinal cord atrophy, suggesting that atrophy is a sensitive biomarker for lower motor neurons degeneration.

Median nerve somatosensory evoked potentials and their high-frequency oscillations in amyotrophic lateral sclerosis

OBJECTIVE

To investigate sensory cortical changes in amyotrophic lateral sclerosis (ALS), we studied somatosensory evoked potentials (SEPs) and their high-frequency oscillation potentials.

METHODS

Subjects were 15 healthy volunteers and 26 ALS patients. Median nerve SEPs were recorded and several peaks of oscillations were obtained by digitally filtering raw SEPs. The patients were sorted into three groups according to the level of weakness of abductor pollicis brevis muscle (APB): mild, moderate and severe. The latencies and amplitudes of main and oscillation components of SEP were compared among normal subjects and the three patient groups.

RESULTS

The early cortical response was enlarged in the moderate weakness group, while it was attenuated in the severe weakness group. No differences were noted in the size ratios of oscillations to the main SEP component between the patients and normal subjects. The central sensory conduction time (CCT) and N20 duration were prolonged in spite of normal other latencies.

CONCLUSIONS

The median nerve SEP amplitude changes are associated with motor disturbances in ALS. The cortical potential enhancement of SEPs with moderate weakness in ALS may reflect some compensatory function of the sensory cortex for motor disturbances.

SIGNIFICANCE

The sensory cortical compensation for motor disturbances is shown in ALS, which must be important information for rehabilitation.

Sensory testing in the assessment of laryngeal sensation in patients with amyotrophic lateral sclerosis

OBJECTIVES

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease of unknown cause. Mortality in the population is frequently due to aspiration pneumonia. Although typically considered to be a disorder limited to motor neuron involvement, some investigators have indicated that decreased sensory function in ALS patients additionally contributes to the disease process. The objective of this study was to evaluate laryngopharyngeal sensation in the ALS population in order to quantify the range of sensory deficits and correlate any abnormalities with demographic data to determine which patients are at risk of having sensory deficits.

METHODS

We examined the sensation of the larynx in 22 patients with ALS to determine whether a sensory deficit was present. After completion of a dysphagia questionnaire and medical history, patients underwent flexible endoscopic evaluation of swallowing with sensory testing (FEESST) to evaluate sensory function. Threshold values were determined and recorded for initiation of the adductor reflex.

RESULTS

The results of the sensory and swallowing function assessments performed on 22 patients demonstrate abnormal sensation in 54.5% of the tested population. Asymmetric findings were noted in 75% of these patients. There was no correlation noted between the presence of sensory deficits and the severity or duration of the disease.

CONCLUSIONS

Progressive dysphagia in the ALS population has typically been attributed to muscle weakness. This study points to the presence of sensory deficits in the larynx, which can further affect proper swallowing function.

Evaluation and rehabilitation of patients with adult motor neuron disease

Adult motor neuron disease (amyotrophic lateral sclerosis [ALS]) is a neurodegenerative disorder characterized by loss of motor neurons in the cortex, brain stem, and spinal cord, manifested by upper and lower motor neuron signs and symptoms affecting bulbar, limb, and respiratory musculature. Clinically, the disease course is characterized by progressive weakness, atrophy, spasticity, dysarthria, dysphagia, and respiratory compromise, ultimately resulting in death or mechanical ventilation in the vast majority of patients. Patterns of presentation and pathological features of the disease, along with clinical and electrophysiologic criteria for diagnosis, are discussed in this review. Since 8% to 22% of patients survive more than 10 years without ventilator use, meticulous medical and rehabilitation management is extremely important to ensure optimal health and quality of life in these patients. Major issues in the care of individuals with ALS include weakness and spasticity, impairments in activities of daily living and mobility, communication deficits and dysphagia in those with bulbar involvement, respiratory compromise, fatigue and sleep disorders, pain, and psychosocial distress. Research in ALS changes rapidly, but is currently focused on potential etiologic factors such as glutamate excitotoxicity, role of oxidative stress, autoimmunity to calcium channels, and cytoskeletal abnormalities, as well as related treatment initiatives including glutamate modulators, neurotrophic factors, antioxidants, antiapoptotic factors, and gene therapy. Recently, mutations in the gene encoding Cu/Zn superoxide dismutase were identified in a subset of familial ALS patients. Riluzole, a glutamate antagonist and Na-channel blocker, became the only drug currently approved for treatment of ALS after studies showed a small positive effect on survival. Until a definitive treatment or cure for ALS is found, the multifaceted rehabilitation team approach remains the best hope for improving health and survival in this devastating illness.

Selective attention is impaired in amyotrophic lateral sclerosis--a study of event-related EEG potentials

In humans, selective attention is assumed to be under control of the frontal lobe. A significant proportion of patients with amyotrophic lateral sclerosis (ALS) shows impairments in various tasks touching frontal lobe function. We, therefore, undertook a study of event-related EEG potentials (ERPs) in eight non-demented ALS patients in order to investigate a possible deficit of auditory selective attention: tones were presented in random sequence to the left or right ear, one of which was to be attended. The negative shift of the ERPs evoked by attended tones in relation to unattended tones ('processing negativity': PN) was smaller in ALS patients than in age-matched healthy control persons. This was true for Fz and Cz and for both a slow and a fast presentation rate of the tones. In the patients, reduced PN amplitude correlated with functional motor impairment. The utility of ERP testing to assess impaired frontal lobe function is shown for the first time in ALS patients. The results of our study fit to recent positron emission tomography (PET) and fMRI data.

Multisystem neuronal involvement and sicca complex: broadening the spectrum of complications

We report two patients with multisystem neuronal involvement associated with sicca complex. One had a lower motor neuron syndrome combined with a flaccid bladder and rectum. The second patient had unilateral hearing loss, sensory neuronopathy, Adie's pupils, upper motor neuron signs, and autopsy-proven anterior horn cell degeneration. Our cases lead us to propose that the spectrum of neuronal involvement occurring with sicca syndrome may be wider than is currently appreciated.

Somatosensory evoked potentials elicited by stimulation of lower-limb nerves in amyotrophic lateral sclerosis

To determine lower limb somatosensory modifications in amyotrophic lateral sclerosis (ALS), we studied somatosensory evoked potentials (SEPs) elicited by stimulation of tibial posterior nerves (TP), sural nerves (SN), saphenous internous nerves (SA), and medial plantar nerves (PL) of both limbs in 24 ALS patients, and compared the results with those from 17 normal subjects. Responses were recorded according to the international 10-20 system. Normal sensory conduction velocities of SN, SA and PL and H reflexes in soleus muscles were prerequisites for patient inclusion in this study. The results showed marked alterations in SEPs cortical components of all lower limb nerves, which could be related to abnormal sensory transmission (after spinal N22), or cortical abnormalities. We put forward the hypothesis of impairment of pyramidal control of the sensory system and Clark's column involvement to explain such anomalies. It was concluded that SEPs abnormalities in the lower limbs are a common feature in ALS.

Increasing neurofilament subunit NF-M expression reduces axonal NF-H, inhibits radial growth, and results in neurofilamentous accumulation in motor neurons

The carboxy-terminal tail domains of neurofilament subunits neurofilament NF-M and NF-H have been postulated to be responsible for the modulation of axonal caliber. To test how subunit composition affects caliber, transgenic mice were generated to increase axonal NF-M. Total neurofilament subunit content in motor and sensory axons remained essentially unchanged, but increases in NF-M were offset by proportionate decreases in both NF-H and axonal cross-sectional area. Increase in NF-M did not affect the level of phosphorylation of NF-H. This indicates that (a) in vivo NF-H and NF-M compete either for coassembly with a limiting amount of NF-L or as substrates for axonal transport, and (b) NF-H abundance is a primary determinant of axonal caliber. Despite inhibition of radial growth, increase in NF-M and reduction in axonal NF-H did not affect nearest neighbor spacing between neurofilaments, indicating that cross-bridging between nearest neighbors does not play a crucial role in radial growth. Increase in NF-M did not result in an overt phenotype or neuronal loss, although filamentous swellings in perikarya and proximal axons of motor neurons were frequently found.

Somatosensory evoked potentials in the differential diagnosis between spinal cord compression and amyotrophic lateral sclerosis

Spinal cord compression (SCC) often presents a similar clinical picture to amyotrophic lateral sclerosis (ALS). An early differential diagnosis is important because SCC is a potentially treatable clinical disorder. We carried out a longitudinal study of 43 patients with an initial diagnosis of ALS, in order to ascertain the percentage of patients with SCC, and to evaluate the usefulness of somatosensory evoked potentials (SEPs) in early diagnosis. Thirty-three patients had a final diagnosis of ALS and 8 of SCC. SEPs central conduction was abnormal in 3 ALS and 7 SCC patients, respectively (Fisher exact test, p < 0.05). We concluded that SEPs investigation is useful in the differential diagnosis between ALS and SCC patients with pure motor signs.

Motor neuron disease (amyotrophic lateral sclerosis) arising from longstanding primary lateral sclerosis

Three men were initially diagnosed as having primary lateral sclerosis (PLS), but eventually developed amyotrophic lateral sclerosis (ALS) after 7.5, 9, and at least 27 years. Non-familial ALS and PLS might be different manifestations of a single disease or constitute completely distinct entities. The clinical diagnosis of PLS predicts a median survival that is four to five times longer than in ALS.

Sympathetic skin response abnormalities in amyotrophic lateral sclerosis

The sympathetic skin response (SSR) was evaluated in 25 patients with amyotrophic lateral sclerosis (ALS) to assess for involvement of the autonomic nervous system. Twenty-two age-matched normals and 6 patients with muscular dystrophy served as controls. The SSR was intact in all normal volunteers and all patients with muscular dystrophy. The mean SSR latency in the ALS patients was prolonged compared to that of normals (2.29 +/- 0.28 versus 2.13 +/- 0.16 s, P < 0.05). The SSR was absent in one or both legs of 10 ALS patients (40%). Absence or abnormal latency of SSR in patients with ALS without clinical findings of autonomic failure suggests involvement of the autonomic nervous system in addition to the motor system.

Progressive sensory nerve dysfunction in amyotrophic lateral sclerosis: a prospective clinical and neurophysiological study

Sensory nerve function was determined in 19 patients with amyotrophic lateral sclerosis (ALS), using a battery of clinical and neurophysiological tests. This assessment was repeated on 12 patients after intervals of 6-18 months. Twelve controls were also studied. In the ALS group, only 2 patients had noticed mild sensory symptoms and none had sensory signs. Between successive studies the vibration thresholds increased, but not to a significant degree. ALS patients showed a significant fall in amplitude of the sensory nerve action potentials in the median, radial, and sural nerves (P < 0.04); sensory nerve conduction velocity did not alter. The median nerve somatosensory evoked potential N19 latency showed a highly significant increase (P < 0.008). Significant subclinical deterioration in sensory nerve function occurs in ALS, and parallels the progressive motor decline. Neuronal degeneration in ALS is not restricted to motor neurons.

Progressive neuronopathy in transgenic mice expressing the human neurofilament heavy gene: a mouse model of amyotrophic lateral sclerosis

We generated four transgenic mice with a 34 kb genomic fragment including the complete human neurofilament heavy (NF-H) gene. This human NF-H fragment contained all regulatory elements for tissue-specific expression, and in two transgenic lines, human NF-H proteins were produced at levels up to 2-fold the levels of endogenous mouse NF-H protein. By 3-4 months of age, these NF-H transgenics progressively develop neurological defects and abnormal neurofilamentous swellings that are highly reminiscent of those found in amyotrophic lateral sclerosis (ALS). We propose that a modest up-regulation of NF-H cross-linkers can result in an impairment of neurofilament transport, causing neuronal swellings with ensuing axonopathy and muscle atrophy, a mechanism of pathogenesis pertinent to the possible etiology of ALS.

Involvement of peripheral sensory fibers in amyotrophic lateral sclerosis: electrophysiological study of 64 cases

We report electrophysiological findings of conduction along peripheral sensory fibers in 64 patients with amyotrophic lateral sclerosis. Distribution of the values of action potential amplitudes and conduction velocities of peripheral afferent fibers were significantly lower than in normal age-matched controls. Sensory action potential amplitudes (SAPas) were more affected than sensory conduction velocities (SCVs). When single patients were considered, SAPas were slightly but significantly reduced in 22% of the cases (median nerve 17%, ulnar nerve 11%, and sural nerve 22%). A parallel decrease in SCVs and MCVs in 14 patients in whom the study was repeated over a period of time was also found. All these electrophysiological findings are due to progressive neuronopathy of peripheral sensory fibers. A pathogenetic mechanism is proposed.

Abnormalities in the sensory action potential in patients with amyotrophic lateral sclerosis

Sensory function in patients with amyotrophic lateral sclerosis (ALS) is thought to be normal; however, there is convincing morphologic evidence that sensory systems are affected in addition to motor systems. In this study, compound sensory action potentials were recorded with near nerve electrodes from 18 patients with ALS. Up to 1024 responses were averaged at high gain to determine minimum conduction velocity; that is, the conduction velocity of the slowest conducting component of the sensory action potential. Nine of 18 patients had abnormally reduced minimum conduction velocity, even when peak-to-peak amplitude and maximum conduction velocity (calculated from the latency to the initial positive peak) were normal. Only 3 of 18 patients showed abnormalities in peak-to-peak amplitude. Thus, subtle abnormalities in the sensory action potential can be detected in many patients with ALS.

Motor neuron disease (amyotrophic lateral sclerosis)

Amyotrophic lateral sclerosis is an insidiously developing, adult-onset, progressive anterior horn cell degeneration with associated degeneration of descending motor pathways. It has been recognized as an important clinical syndrome since the middle of the 19th century. Despite increasing clinical and research interest in this condition, its cause remains obscure, even in the broadest terms. Epidemiologic characteristics of the disease have been interpreted as evidence of both genetic and environmental causes. A major change in the view of this disease is the widely developing perception that it is a disease of elderly persons more than of middle-aged adults as was previously taught. Etiologic hypotheses encompass a broad range of postulated pathophysiologic mechanisms, and we review these in detail. The clinical limits of the disease can now be better defined by using modern diagnostic techniques. Although interest in supportive symptomatic therapy is growing, no intervention has yet been shown to modify the biologically determined motor system degeneration.

Far-field and cortical somatosensory evoked potentials in motor neuron disease

We examined median somatosensory evoked potentials (SEPs) in 26 patients with sporadic motor neuron disease (MND). SEPs were recorded with multiple scalp derivations, using both the midfront and the earlobe as references for each subject. Central conduction time (CCT) was abnormal in three patients, but only when using the midfront reference. Moreover, an exclusive alteration of the early prerolandic potentials (absent or delayed P20 and/or P22) was noted using the earlobe reference in amyotrophic lateral sclerosis and in progressive bulbar palsy (54% and 50% of patients, respectively) but not in progressive muscular atrophy. These findings correlated with clinical evidence of upper motor neuron signs and with the severity of the disease. In agreement with recent views regarding the sources of the early anterior cortical responses, neuronal loss in the motor cortex may be considered as affecting the generator sites of these potentials.

Animal models of amyotrophic lateral sclerosis and the spinal muscular atrophies

The causes of human amyotrophic lateral sclerosis (ALS) and the spinal muscular atrophies (SMA) are, almost without exception, unknown. This ignorance has stimulated the search for animal models to obtain insight into the etiology, pathogenesis and biochemical mechanisms underlying the human disorders. None of the 38 animal models, described in this review, provides an exact animal copy of a specific human motor neuron disease. Most of the models reproduce certain structural or physiological aspects of their human counterparts. The various experimental models can be classified according to the pathogenetic mechanism involved and according to the structural changes observed. Models based on experimentally induced disease, include heavy metals and trace elements (lead intoxication in guinea pigs, rabbits, rats, cats and primates; mercury intoxication in rats; aluminium intoxication in rabbits; swayback in goat kids; calcium and magnesium deficient rabbits and primates and calcium deficient cynomolgus monkeys), toxins (IDPN, vincristine, vinblastine, podophyllotoxin, colchicine, maytansine, maytanprine, L-BMAA, lectins, adriamycin), nutritional factors (ascorbic acid deficient guinea pigs), virus infection (spongiform polioencephalomyelitis, attenuated poliovirus, lactate dehydrogenase-elevating virus), and immunological factors (immunization with motor neurons). Hereditary models comprise hereditary canine spinal muscular atrophy, hereditary neurogenic amyotrophy in the pointer dog, Stockard paralysis, Swedish Lapland dog paralysis, "wobbler" mouse, "shaker" calf, and hereditary spinal muscular atrophy in zebra foals, crossbred rabbits,

Multimodality evoked potentials in amyotrophic lateral sclerosis

Visual, brainstem auditory and somatosensory evoked potentials to medial nerve stimulation were recorded in 27 patients affected by amyotrophic lateral sclerosis. VEP N75, P100, N140, N75-P100 latencies and P100 amplitude, BAEP I-III, III-V and I-V interpeak-latencies were within normal limits in all ALS patients. Somatosensory evoked potentials were abnormally delayed in 8 patients: in 3 arms because of a delayed N9-N13 latency, in 9 arms because of a delayed N13-N19 latency.

Sensory neuron degeneration in familial Kugelberg-Welander disease

A 53 year old man developed symptoms of motor neuron disease in childhood. There was a family history of a similar disorder and it was felt to represent a form of Kugelberg-Welander disease. In addition to the motor deficits, sensory abnormalities in his legs were documented during life. Autopsy revealed anterior horn cell loss throughout the length of the spinal cord, with preservation of the phrenic nucleus. The lumbar dorsal root ganglia showed active degeneration of sensory neurons, with nuclear changes exceeding cytoplasmic ones. The fasciculus gracilis showed Wallerian degeneration. The findings provide direct evidence that sensory neurons can degenerate in some forms of motor neuron disease, and that the "demyelination" or "degeneration" of posterior columns sometimes seen in the various forms of motor neuron disease may actually be secondary to cell body disease in the dorsal root ganglia.