Disinhibition of sensory cortex in patients with amyotrophic lateral sclerosis

Brain metabolic signatures in patients with genetic and nongenetic amyotrophic lateral sclerosis

AIMS

To study the brain metabolic signature in Chinese amyotrophic lateral sclerosis (ALS) patients and compare the difference in brain metabolic patterns between ALS with and without genetic variants.

METHODS

We included 146 patients with ALS and 128 healthy controls (HCs). All patients with ALS underwent genetic testing to screen for ALS related genetic variants and were then divided into genetic (n = 22) and nongenetic ALS (n = 93) subgroups. All participants underwent brain 18 F-FDG-PET scans. Group comparisons were performed using the two-sample t-test model of SPM12.

RESULTS

We identified a large of hypometabolic clusters in ALS patients as compared with HCs, especially in the bilateral basal ganglia, midbrain, and cerebellum. Moreover, hypometabolism in the bilateral temporal lobe, precentral gyrus and hypermetabolism in the left anterior cingulate, occipital lobe, and bilateral frontal lobe were also found in ALS patients as compared with HCs. Compared with nongenetic ALS patients, genetic ALS patients showed hypometabolism in the right postcentral gyrus, precuneus, and middle occipital gyrus. The incidence of sensory disturbance in patients with genetic ALS was higher than that in patients with nongenetic ALS (5 of 22 [22.72%] vs. 7 of 93 [7.52%], p = 0.036).

CONCLUSIONS

Our investigation provided unprecedented evidence of relative hypometabolism in the midbrain and cerebellum in ALS patients. Genetic ALS patients showed a specific signature of brain metabolism and a higher incidence of sensory disturbance, indicating that genetic factors may be an underlying cause affecting the brain metabolism and increasing the risk of sensory disturbance in ALS.

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.

Dysregulated cortical synaptic plasticity under methyl-CpG binding protein 2 deficiency and its implication in motor impairments

Caused by the mutation of methyl-CpG binding protein 2 (MeCP2), Rett syndrome leads to a battery of severe neural dysfunctions including the regression of motor coordination and motor learning. Current understanding has revealed the motor cortex as the critical region mediating voluntary movement. In this review article, we will summarize major findings from human patients and animal models regarding the cortical synaptic plasticity under the regulation of MeCP2. We will also discuss how mutation of MeCP2 leads to the disruption of cortical circuitry homeostasis to cause motor deficits. Lastly, potential values of physical exercise and neuromodulation approaches to recover neural plasticity and motor function will be evaluated. All of this evidence may help to accelerate timely diagnosis and effective interventions for Rett syndrome patients.

Neuronal Hyperexcitability and Free Radical Toxicity in Amyotrophic Lateral Sclerosis: Established and Future Targets

Amyotrophic lateral sclerosis (ALS) is a devastating disease with evidence of degeneration involving upper and lower motor neuron compartments of the nervous system. Presently, two drugs, riluzole and edaravone, have been established as being useful in slowing disease progression in ALS. Riluzole possesses anti-glutamatergic properties, while edaravone eliminates free radicals (FRs). Glutamate is the excitatory neurotransmitter in the brain and spinal cord and binds to several inotropic receptors. Excessive activation of these receptors generates FRs, inducing neurodegeneration via damage to intracellular organelles and upregulation of proinflammatory mediators. FRs bind to intracellular structures, leading to cellular impairment that contributes to neurodegeneration. As such, excitotoxicity and FR toxicities have been considered as key pathophysiological mechanisms that contribute to the cascade of degeneration that envelopes neurons in ALS. Recent advanced technologies, including neurophysiological, imaging, pathological and biochemical techniques, have concurrently identified evidence of increased excitability in ALS. This review focuses on the relationship between FRs and excitotoxicity in motor neuronal degeneration in ALS and introduces concepts linked to increased excitability across both compartments of the human nervous system. Within this cellular framework, future strategies to promote therapeutic development in ALS, from the perspective of neuronal excitability and function, will be critically appraised.

Pharyngeal electrical stimulation in amyotrophic lateral sclerosis: a pilot study

Background:

Patients with amyotrophic lateral sclerosis (ALS) suffer from dysphagia that increases the risk for aspiration, pneumonia and weight loss. Pharyngeal electrical stimulation (PES) is a therapeutic technique that applies electric stimuli to the patient’s pharynx in order to improve swallowing based on the principle of cortical plasticity and reorganization. Previous studies have demonstrated positive effects in patients with various neurological diseases.

Objective:

This study was initiated to investigate the effect of PES on swallowing function in patients with ALS.

Methods:

In all, 20 ALS patients with severe dysphagia [characterized by a Penetration Aspiration Scale (PAS) of at least 4 in thin liquid] were randomized to receive either PES for 10 min at 3 consecutive days in addition to Standard Logopaedic Therapy (SLT) or SLT alone. Swallowing function was evaluated by Fiberoptic Endoscopic Evaluation of Swallowing (FEES) at five timepoints: at baseline, 1 day, 4 days, 3 weeks and 3 months after treatment. Primary endpoint was the severity of penetrations or aspirations as classified by PAS. Secondary endpoints were adverse events, dysphagia-related quality of life, Swallowing Quality of Life (SWAL-QOL), Dysphagia Severity Rating Scale (DSRS), residues, leaking, ALS Functional Rating Scale Revised (ALSFRS-R), and the performance in Clinical Evaluation of Swallowing (CES). The trial is registered under the name of ‘Pharyngeal Electrical Stimulation in Amyotrophic Lateral Sclerosis’ with ClinialTrials.gov, number NCT03481348 (https://clinicaltrials.gov/ct2/show/NCT03481348).

Results:

Both groups combined showed a significant improvement (p = 0.003) of median Total-PAS from 3.6 [interquartile range (IQR) = 2.9–5.0] at baseline to 2.3 (IQR = 1.8–4.0) 1 day after treatment. During subsequent study visits, PAS increased again but remained below baseline. PES and control group did not differ significantly 1 day after intervention (p = 0.32). Similar effects were found in the majority of secondary endpoints.

Interpretation:

The findings suggest that PES may not provide an additional positive effect on swallowing function in ALS. SLT seems to yield at least short-term positive effects on swallowing function and swallowing-specific life quality in ALS.

Registration: ClinialTrials.gov: NCT03481348

Non-Motor Symptoms of Amyotrophic Lateral Sclerosis: A Multi-Faceted Disorder

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive degeneration of motor pathways. A growing body of evidence from recent years suggests that ALS results in a wide range of non-motor symptoms as well, which can have a significant impact on patients' quality of life. These symptoms could also, in turn, provide useful information as biomarkers for disease progression, and can shed insight on ALS mechanisms. Here we aim to review a wide range of non-motor symptoms of ALS, with emphasis on their importance to research and clinical treatment of patients.

Enlarged high frequency oscillations of the median nerve somatosensory evoked potential and survival in amyotrophic lateral sclerosis

OBJECTIVE

A large N20 and P25 of the median nerve somatosensory evoked potential (SEP) predicts short survival in amyotrophic lateral sclerosis (ALS). We investigated whether high frequency oscillations (HFOs) over N20 are enlarged and associated with survival in ALS.

METHODS

A total of 145 patients with ALS and 57 healthy subjects were studied. We recorded the median nerve SEP and measured the onset-to-peak amplitude of N20 (N20o-p), and peak-to-peak amplitude between N20 and P25 (N20p-P25p). We obtained early and late HFO potentials by filtering SEP between 500 and 1 kHz, and measured the peak-to-peak amplitude. We followed up patients until endpoints (death or tracheostomy) and analyzed the relationship between SEP or HFO amplitudes and survival using a Cox analysis.

RESULTS

Patients showed larger N20o-p, N20p-P25p, and early and late HFO amplitudes than the control values. N20p-P25p was associated with survival periods (p = 0.0004), while early and late HFO amplitudes showed no significant association with survival (p = 0.4307, and p = 0.6858, respectively).

CONCLUSIONS

The HFO amplitude in ALS is increased, but does not predict survival.

SIGNIFICANCE

The enlarged HFOs in ALS might be a compensatory phenomenon to the hyperexcitability of the sensory cortex pyramidal neurons.

Diagnostics of Amyotrophic Lateral Sclerosis: Up to Date

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by gradual loss of upper and lower motor neurons and their pathways, usually without affecting the extraocular and sphincter muscles. The cause of the disease is not yet known. It is a chain of subsequent events, ending in programmed cell death in selective neuronal subpopulations. The prognosis for survival is rather short with a median of 2 to 4 years. Survival may be prolonged based on prompt diagnosis, ALS subtype and proper management with supportive treatment (tracheostomy, gastrostomy, etc.). According to the clinical picture, the typical form of ALS with upper and lower motoneuron involvement and progressive bulbar paralysis with bulbar muscle involvement is observed. The ALS form with progressive muscle atrophy, where only the lower motoneuron is affected, and primary lateral sclerosis with only upper motoneuron damage are rare. Familiar forms of ALS (FALS) associated with specific genes (the most common is C9orf72) have been discovered. FALS is usually associated with dementia (frontotemporal lobar dementia, FTLD), behavioral disorders, cognitive dysfunction and impairment of executive functions. The diagnosis of ALS is determined by excluding other conditions and utilizing clinical examinations, laboratory and genetic tests and nerve conduction/needle electromyography studies (EMG). Needle EMG records abnormal activities at rest and looks for neurogenic patterns during muscle contraction. Motor evoked potentials after transcranial magnetic stimulation remain the test of choice to identify impairment of upper motor neurons. New biochemical, neurophysiological and morphological biomarkers are extensively studied as early diagnostic and prognostic factors and have implications for clinical trials, research and drug development.

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.