Association of paraspinal and diaphragm denervation in ALS

The impact of upper and lower motor neuron burden on diagnostic certainty, and clinical course of spinal-onset amyotrophic lateral sclerosis: a cluster-based approach

BACKGROUND

Upper motor neuron (UMN) and lower motor neuron (LMN) involvement represent the core clinical features of amyotrophic lateral sclerosis (ALS). Several studies divided patients into prevalent UMN and LMN impairment phenotypes to investigate the association between motor systems impairments and ALS clinical course. However, this distinction was somehow heterogeneous and significantly affected the comparability across studies.

AIMS

This study aimed to investigate whether patients spontaneously segregate based on the extent of UMN and LMN involvement without a-priori categorization and to identify potential clinical and prognostic features of different clusters.

METHODS

Eighty-eight consecutive spinal-onset ALS patients were referred to an ALS tertiary center between 2015 and 2022. UMN and LMN burden was assessed with the Penn Upper Motor Neuron scale (PUMNS) and the Devine score, respectively. PUMNS and LMN scores were normalized into 0-1 and analyzed using a two-step cluster analysis and the Euclidean distance measure. The Bayesian Information Criterion was used to determine the cluster number. Demographic and clinical variables were tested for differences among the clusters.

RESULTS

Three distinct clusters emerged at cluster analysis. Patients in "cluster-1" showed moderate UMN and severe LMN involvement, corresponding to the typical ALS phenotype. Patients in "cluster-2" showed mild LMN and severe UMN damage, corresponding to a predominant UMN phenotype, while "cluster-3" patients showed mild UMN and moderate LMN damage, corresponding to a predominant LMN phenotype. Patients in "cluster-1" and "cluster-2" showed a higher prevalence of definite ALS than those in "cluster-3" (61% and 46 vs 9%, p < 0.001). "Cluster-1" patients had a lower median ALSFRS-r score compared to both "cluster-2" and 3 patients (27 vs 40 and 35, < 0.001). "Cluster-1" (HR: 8.5; 95% CI 2.1-35.1 and p = 0.003) and 3 (HR: 3.2; 95% CI 1.1-9.1; p = 0.03) were associated with shorter survival than those in "cluster-2".

CONCLUSIONS

Spinal-onset ALS can be categorized into three groups according to LMN and UMN burden. The UMN burden is related to higher diagnostic certainty and broader disease spread, while LMN involvement is associated with higher disease severity and shorter survival.

Widespread Mislocalization of FUS Is Associated With Mitochondrial Abnormalities in Skeletal Muscle in Amyotrophic Lateral Sclerosis With FUS Mutations

Mutations in the fused in sarcoma (FUS) gene have been reported to be the most common genetic cause of early-onset amyotrophic lateral sclerosis (ALS); cytoplasmic inclusions containing FUS protein are the predominant pathological feature. Recent studies indicated that mutant FUS impaired neuromuscular junctions and induced muscle intrinsic toxicity in cell and animal models. However, the role of FUS in muscle degeneration remains unclear. In this study, we investigated FUS protein distribution in skeletal muscle fibers in ALS-FUS. Our data show that cytoplasmic mislocalized FUS in the unaggregated form represented a remarkable pathological feature in affected muscle fibers in ALS-FUS. Additional studies found that cytoplasmic FUS colocalized with some mitochondria and was associated with mitochondrial swelling and disorganized cristae. RNA sequencing and quantitative real-time polymerase chain reaction analyses indicated downregulation of the key subunits of mitochondrial oxidative phosphorylation complexes in the affected skeletal muscle in ALS-FUS patients. Further immunoblot analysis showed increased levels of FUS, but decreased levels of Cox I (subunit of complex IV) in ALS-FUS patients compared with age-matched controls. This is the first demonstration of the close association of cytoplasmic mislocalized FUS with mitochondrial dysfunction in skeletal muscle, implicating the presence of a cell-autonomous mechanism in muscle degeneration in ALS.

Electrophysiological assessment of respiratory function

While the traditional lung function tests are used to assess lung capacity and pulmonary function, they cannot evaluate respiratory driving function and the integrity of the conduction pathway from the central nervous system to the respiratory motor neuron in the spinal cord and to the diaphragm. The inspiratory trigger is sent from the central nervous system through the phrenic nerve and drives the diaphragm to generate inspiratory movement. Therefore, phrenic nerve stimulation and diaphragmatic electromyography are two fundamental methods to assess respiratory function. There are several useful tools to assess respiratory motor system including electrical or magnetic phrenic nerve stimulation, diaphragmatic needle electromyography, and diaphragmatic ultrasound. By these means, physicians can assess current respiratory status in different neurological diseases that affect respiratory muscles, follow-up of the severity of respiratory impairment, help to predict the chance of successfully weaning from ventilatory support, and confirm clinical diagnoses such as diaphragmatic myoclonus. Although some of these tests require special training, applying these neurophysiological assessments in clinical practice is highly recommended.

Electromyographic findings in primary lateral sclerosis during disease progression

OBJECTIVE

To characterize electromyographic (EMG) findings in patients with primary lateral sclerosis (PLS) during the disease course.

METHODS

In PLS patients we scored spontaneous activity and motor unit action potential (MUP) pattern on EMG. We compared patients according to lower (group A) and higher (group B) EMG scores. EMG studies were repeated at intervals longer than 11 months; two or three repeat studies were required for inclusion in the analysis.

RESULTS

We studied 22 patients. Fasciculation potentials were found in 13 and fibrillations/positive sharp waves (fibs/sw) in 3 patients. Both were stable over time. Most patients had MUP abnormalities (n = 17), with worsening in the lower limbs in patients with three evaluations (p = 0.010). Compared to group A (n = 12), patients of group B (n = 10) had a significant shorter disease duration (median 10.9 vs 15.2 years, p < 0.001), lower functional score at both first (39 vs 45, p = 0.034) and last (29 vs 38, p = 0.003) evaluations, and had a faster functional decline (0.19 vs 0.08, p = 0.004).

CONCLUSIONS

Most PLS patients showed minor and stable EMG abnormalities, without progression to ALS. Patients with more EMG abnormalities have a faster progression.

SIGNIFICANCE

EMG abnormalities in most PLS patients are minor and stable.

Prognostic value of EMG genioglossus involvement in amyotrophic lateral sclerosis

OBJECTIVE

To evaluate the prognostic value of needle electromyography (EMG) genioglossus involvement in patients with amyotrophic lateral sclerosis (ALS) at diagnosis.

METHODS

We separately explored the prognostic value of clinical bulbar lower motor neuron (LMN) signs and EMG genioglossus involvement using Cox proportional hazard models adjusted for age, gender, diagnostic delay, presence of bulbar upper motor neuron (UMN) signs, EMG cervical and lumbosacral region involvement, ALSFRS-R score and C9Orf72 gene status. Then, we compared the prognostic value of EMG masseter and genioglossus abnormalities in a subset of patients in whom both muscles were analysed.

RESULTS

103 ALS patients were included in the study. Neurophysiological genioglossus involvement was associated with a shorter survival (p = 0.002), a shorter time to moderate dysphagia (p = 0.0001) and to severe dysarthria (p = 0.012). Its prognostic value was still evident in patients without clinical bulbar LMN signs. Bulbar clinical LMN signs were only associated with an earlier onset of moderate dysphagia (p = 0.0001). EMG masseter abnormalities did not reach statistical significance with regard to all the clinical milestones.

CONCLUSIONS

Genioglossus EMG at diagnosis could provide important information about ALS progression rate. The masseter muscle seems to be less involved in ALS.

SIGNIFICANCE

EMG genioglossus involvement is a prognostic factor in ALS.

The Skeletal Muscle Emerges as a New Disease Target in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that leads to progressive degeneration of motor neurons (MNs) and severe muscle atrophy without effective treatment. Most research on ALS has been focused on the study of MNs and supporting cells of the central nervous system. Strikingly, the recent observations of pathological changes in muscle occurring before disease onset and independent from MN degeneration have bolstered the interest for the study of muscle tissue as a potential target for delivery of therapies for ALS. Skeletal muscle has just been described as a tissue with an important secretory function that is toxic to MNs in the context of ALS. Moreover, a fine-tuning balance between biosynthetic and atrophic pathways is necessary to induce myogenesis for muscle tissue repair. Compromising this response due to primary metabolic abnormalities in the muscle could trigger defective muscle regeneration and neuromuscular junction restoration, with deleterious consequences for MNs and thereby hastening the development of ALS. However, it remains puzzling how backward signaling from the muscle could impinge on MN death. This review provides a comprehensive analysis on the current state-of-the-art of the role of the skeletal muscle in ALS, highlighting its contribution to the neurodegeneration in ALS through backward-signaling processes as a newly uncovered mechanism for a peripheral etiopathogenesis of the disease.

Spreading in ALS: The relative impact of upper and lower motor neuron involvement

Objective

To investigate disease spread in amyotrophic lateral sclerosis (ALS), and determine the influence of lower (LMN) and upper motor neuron (UMN) involvement.

Methods

We assessed disease spread in ALS in 1376 consecutively studied patients, from five European centers, applying an agreed proforma to assess LMN and UMN signs. We defined the pattern of disease onset and progression from predominant UMN or lower motor neuron (LMN) dysfunction in bulbar, upper limbs, lower limbs, and thoracic regions Non‐linear regression analysis was applied to fit the data to a model that described the relation between two random variables, graphically represented by an inverse exponential curve. We analyzed the probability, rate of spread, and both combined (area under the curve).

Results

We found that progression was more likely and quicker to or from the region of onset to close spinal regions. When the disease had a limb onset, bulbar motor neurons were more resistant. Furthermore, in the same time frame more patients progressed from bulbar to lower limbs than vice‐versa, whether predominantly UMN or LMN involvement. Patients with initial thoracic involvement had a higher probability for rapid change. The presence of predominant UMN signs was associated with a faster caudal progression.

Interpretation

Contiguous progression was leading pattern, and predominant UMN involvement is important in shortening the time for cranial‐caudal spread. Our results can best be fitted to a model of independent LMN and UMN degeneration, with regional progression of LMN degeneration mostly by contiguity. UMN lesion causes an acceleration of rostral‐caudal LMN loss.

Quantitative electromyography: Normative data in paraspinal muscles

BACKGROUND

Quantitative electromyography of paraspinal muscle is a valuable diagnostic tool, but normative data are lacking.

METHODS

Needle electromyography (EMG) was obtained in 65 healthy subjects (49% men, 51% women) aged 21 to 82 years at C7, Th10, and L5 segments bilaterally. The incidence of spontaneous activity; motor unit potential (MUP) amplitudes, durations, and the incidence of polyphasic potentials; and the recruitment pattern at maximal voluntary contraction (MVC) were evaluated.

RESULTS

The incidence of fibrillation potentials was similar to limb muscles. The mean MUP duration and amplitude, and the amplitude at MVC increased caudally, while the incidence of polyphasic potentials was similar at all levels. EMG parameters did not correlate with sex or age.

CONCLUSIONS

In contrast to limb muscles, EMG parameters did not change with age, while polyphasic potentials were more frequent in paraspinal muscle than in limb muscles. The EMG gradient suggests larger motor units at more caudal segments.

Respiratory muscle activation patterns during maximum airway pressure efforts are different in women and men

Maximum inspiratory and expiratory pressure values (PI_max and PE_max) are indirect measures of respiratory muscle strength that, in healthy adults, are known to be significantly lower in women compared to men. In part, sex differences in breathing kinematics, lung size, body composition, muscle mass, and muscle fiber composition are thought to be responsible for these effects. However, it is not known whether respiratory muscle activation during maximum respiratory efforts is also sex-specific. In this study, we addressed whether respiratory multi-muscle activation patterns during PI_max and PE_max efforts are different between healthy women and men. Forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), PI_max, PE_max, and surface electromyographic (sEMG) activity recorded from respiratory muscles during these maximum airway pressure efforts were obtained in 13 women and 11 men. Percent predicted values of FVC and FEV₁ were not significantly different in these two groups (women vs. men: 112 ± 14 vs. 105 ± 15%, p = 0.29; and 92 ± 12 vs. 93 ± 13, p = 0.82, Mean ± SD, respectively), while PI_max and PE_max measures were significantly lower in women compared to men (68 ± 16 vs. 88 ± 19 cmH₂O, p = 0.011; and 69 ± 13 vs. 94 ± 17, p = 0.0004, respectively). Using vector-based methodology, by calculating the Similarity Index (SI) as measure of the resemblance between two sEMG patterns and the Magnitude (Mag) representing the overall amount sEMG during motor task, we have found that although the Mag values for both PI_max and PE_max tasks were not significantly different in two groups, the SIs revealed significant sex-dependent differences in muscle activation patterns (0.89 ± 0.08 vs. 0.97 ± 0.02, p = 0.016; and 0.77 ± 0.11 vs. 0.92 ± 0.04, p = 0.0006, respectively). During the PI_max effort, presented as the percentage of total sEMG amplitude, activity of upper trapezius muscle was significantly larger (p = 0.001) while activation of rectus abdominus, oblique, and lower paraspinal muscles were significantly smaller (p = 0.002, p = 0.040, p = 0.005, respectively) in women when compared to the men (50 ± 21 vs. 22 ± 11%; 2 ± 2 vs. 8 ± 7; 4 ± 3 vs. 9 ± 7, 2 ± 3 vs. 7 ± 6, respectively). During PE_max effort, the percentage of sEMG activity were significantly larger in upper and lower trapezius, and intercostal muscles (p = 0.038, p = 0.049, p = 0.037, respectively) and were significantly smaller in pectoralis, rectus abdominus, and oblique muscles (p = 0.021, p < 0.0001, p = 0.048, respectively) in women compared to men (16 ± 10 vs. 9 ± 4%; 16 ± 9 vs. 8 ± 5; 36 ± 12 vs. 25 ± 9; 6 ± 3 vs. 15 ± 5; 14 ± 5 vs. 20 ± 7, respectively). These findings indicate that respiratory muscle activation patterns during maximum airway pressure efforts in healthy individuals are sex-specific. This information should be considered during respiratory motor control evaluation and treatment planning for people with compromised respiratory motor function.

Phosphorylated TDP-43 (pTDP-43) aggregates in the axial skeletal muscle of patients with sporadic and familial amyotrophic lateral sclerosis

Muscle atrophy with weakness is a core feature of amyotrophic lateral sclerosis (ALS) that has long been attributed to motor neuron loss alone. However, several studies in ALS patients, and more so in animal models, have challenged this assumption with the latter providing direct evidence that muscle can play an active role in the disease. Here, we examined the possible role of cell autonomous pathology in 148 skeletal muscle samples from 57 ALS patients, identifying phosphorylated TAR DNA-binding protein (pTDP-43) inclusions in the muscle fibers of 19 patients (33.3%) and 24 tissue samples (16.2% of specimens). A muscle group-specific difference was identified with pTDP-43 pathology being significantly more common in axial (paraspinous, diaphragm) than appendicular muscles (P = 0.0087). This pathology was not significantly associated with pertinent clinical, genetic (c9ALS) or nervous system pathologic data, suggesting it is not limited to any particular subgroup of ALS patients. Among 25 non-ALS muscle samples, pTDP-43 inclusions were seen only in the autophagy-related disorder inclusion body myositis (IBM) (n = 4), where they were more diffuse than in positive ALS samples (P = 0.007). As in IBM samples, pTDP-43 aggregates in ALS were p62/ sequestosome-1-positive, potentially indicating induction of autophagy. Phospho-TDP-43-positive ALS and IBM samples also showed significant up-regulation of TARDBP and SQSTM1 expression. These findings implicate axial skeletal muscle as an additional site of pTDP-43 pathology in some ALS patients, including sporadic and familial cases, which is deserving of further investigation.

Association Between Rectus Abdominis Denervation and Ventilation Dysfunction in Patients with Amyotrophic Lateral Sclerosis

Background:

Spontaneous potentials in electromyography (EMG) of paraspinal muscles are associated with diaphragm denervation and, therefore, poor respiratory function in amyotrophic lateral sclerosis (ALS) is understandable. EMG changes in the rectus abdominis (RA) display an effect similar to those in paraspinal muscles with respect to the function of lower motor neurons in the thoracic spinal cord. The RA denervation was examined to determine its association with ventilation dysfunction in ALS.

Methods:

We collected the clinical data of 128 patients with sporadic ALS in Department of Neurology of Peking University Third Hospital from 2009 to 2013. EMG, Revised ALS Functional Rating Scale (ALSFRS-R) and forced vital capacity (FVC) were performed in all patients and the differences in the EMG changes in RA between those with and without FVC ≥ 80% were analysed.

Results:

The mean FVC value was 83.4% ± 17.1% (range: 45%–131%) of the predicted value. A total of 79 patients displayed FVC ≥80%, and 49 patients displayed FVC <80%. Compared with the patients displaying a normal FVC (60/79, 75.9%), spontaneous activity in RA was significantly different among those patients displaying an FVC <80% (47/49, 95.9%). In addition, spontaneous potentials in RA were more frequently detected in patients exhibiting dyspnea (32/33, 97.0%) than in patients without dyspnea (75/95, 78.9%).

Conclusion:

Spontaneous potentials in RA are associated with ventilation dysfunction and dyspnea in ALS patients.

Assessment of pulmonary function in amyotrophic lateral sclerosis: when can polygraphy help evaluate the need for non-invasive ventilation?

BACKGROUND

Non-invasive positive-pressure ventilation (NPPV) is an established, effective, long-term treatment for patients with amyotrophic lateral sclerosis (ALS), but the correct indicators for the establishment of NPPV have not been defined.

METHODS

In this retrospective study, records (spirometry, nocturnal polygraphy, nocturnal blood gases) of 131 patients with ALS were reviewed in order to evaluate the role of polygraphy for prediction of respiratory failure in ALS.

RESULTS

The patient group reporting with versus without dyspnoea had significantly lower values on the revised ALS-Functional Rating Scale (ALSFRS-R), vital capacity (VC), forced VC (FVC), arterial oxygen saturation and arterial oxygen tension readings, including a higher apnoea-hypopnoea index. 23 patients, who did not report about dyspnoea, had an FVC of <75%. Nocturnal hypoventilation was observed in 67% of the patients with ALS independent of their ALSFRS-R. The patient group with nocturnal hypoventilation was characterised by a significantly lower VC, FVC and maximal static inspiratory pressure compared with the group without nocturnal hypoventilation. However, also in the absence of nocturnal hypoventilation, 8 patients had a VC <50% as predicted.

DISCUSSION

Our study shows that in patients not reporting dyspnoea and having an FVC of >75%, nocturnal hypoventilation was observed in nearly every second patient. Therefore, for the question of whether NPPV should be initiated, polygraphy does not provide useful additional information if the FVC is already <75% as predicted. However, in patients with more or less normal lung function parameters or where lung spirometry cannot perform adequately (eg, bulbar ALS), it can provide sufficient evidence for the need of NPPV.

An Assessment of Possible Neuropathology and Clinical Relationships in 46 Sporadic Amyotrophic Lateral Sclerosis Patient Autopsies

BACKGROUND

Recent studies have suggested overlapping pathological features among motor neuron, cognitive and neurodegenerative diseases.

AIMS/METHODS

Secondary analysis of 46 amyotrophic lateral sclerosis (ALS) patient autopsies was performed to independently assess pathological feature prevalence (e.g. percent of patients with any positive finding), degree of severity (e.g. mild, moderate, severe), and 2,200+ potential clinical/neuropathological correlations. The possible impact of gender, onset age, onset type (limb vs. bulbar), riluzole treatment, and severe TDP-43 pathology was assessed within patient subgroups.

RESULTS

Assessed features (prevalence, severity) include: lateral corticospinal tract degeneration (89%, moderate); Purkinje cell loss (85%, mild); localized neuronal loss (83%, mild to moderate); TDP-43 inclusions (80%, moderate); Betz cell loss (76%, mild); neurofibrillary tangles (78%, severe); anterior corticospinal tract degeneration (72%, moderate); spinal ventral root atrophy (65%, moderate); atherosclerosis (35%, mild); β-amyloid (35%, mild); tauopathy/tau inclusions (17%, mild); ventricular dilation (13%, mild); Lewy body formation (11%, mild); microinfarcts (7%, mild); and α-synuclein (4%, mild). Twenty-two percent of patients met criteria for Alzheimer's disease (AD) and 26% for frontotemporal lobar degeneration. Substantial differences were identified in the AD group and in the different onset age groups.

CONCLUSION

Our findings support the hypothesis that ALS and its variants could comprise a larger neuropathological continuum.

Characterization of intercostal muscle pathology in canine degenerative myelopathy: a disease model for amyotrophic lateral sclerosis

Dogs homozygous for missense mutations in the SOD1 gene develop a late-onset neuromuscular disorder called degenerative myelopathy (DM) that has many similarities to amyotrophic lateral sclerosis (ALS). Both disorders are characterized by widespread progressive declines in motor functions, accompanied by atrophic changes in the descending spinal cord tracts. Some forms of ALS are also associated with SOD1 mutations. In end-stage ALS, death usually occurs as a result of respiratory failure from severe functional impairment of respiratory muscles. The mechanisms that lead to this loss of function are not known. Dogs with DM are euthanized at all stages of disease progression, providing an opportunity to characterize the onset and progression of any pathological changes in the respiratory muscles that may precede respiratory failure. To characterize such potential disease-related pathology, we evaluated intercostal muscles from Boxer and Pembroke Welsh Corgi dogs that were euthanized at various stages of DM disease progression. DM was found to result in intercostal muscle atrophy, fibrosis, increased variability in muscle fiber size and shape, and alteration in muscle fiber type composition. This pathology was not accompanied by retraction of the motor neuron terminals from the muscle acetylcholine receptor complexes, suggesting that the muscle atrophy did not result from physical denervation. These findings provide a better understanding of the mechanisms that likely lead to respiratory failure in at least some forms of ALS and will be useful in the development and evaluation of potential therapeutic interventions using the DM model.

Ventilatory control in ALS

Amyotrophic lateral sclerosis (ALS) is a fatal, progressive neurodegenerative disease. ALS selectively causes degeneration in upper and lower (spinal) motor neurons, leading to muscle weakness, paralysis and death by ventilatory failure. Although ventilatory failure is generally the cause of death in ALS, little is known concerning the impact of this disorder on respiratory motor neurons, the consequences of respiratory motor neuron cell death, or the ability of the respiratory control system to "fight back" via mechanisms of compensatory respiratory plasticity. Here we review known effects of ALS on breathing, including possible effects on rhythm generation, respiratory motor neurons, and their target organs: the respiratory muscles. We consider evidence for spontaneous compensatory plasticity, preserving breathing well into disease progression despite dramatic loss of spinal respiratory motor neurons. Finally, we review current and potential therapeutic approaches directed toward preserving the capacity to breathe in ALS patients.

Respiratory therapies for amyotrophic lateral sclerosis: a primer

Respiratory complications are a common cause of morbidity and mortality in amyotrophic lateral sclerosis (ALS). Treatment of respiratory insufficiency with noninvasive ventilation (NIV) improves ALS patients' quality of life and survival. Evidence-based practice guidelines for the management of ALS patients recommend treatment of respiratory insufficiency with NIV as well as consideration of insufflation/exsufflation to improve clearance of airway secretions. Despite these recommendations respiratory therapies remain underused. In this review we provide a practical guide for the clinician to prescribe and manage respiratory therapies for the patient with ALS.

Diaphragm pacing in amyotrophic lateral sclerosis: a literature review

Amyotrophic lateral sclerosis (ALS) remains a rapidly progressive fatal degenerative disease of motor neurons for which there are few interventions to slow disease progression or improve quality of life. A diaphragm pacing system was approved by the U.S. Food and Drug Administration in September 2011 for ALS under a Humanitarian Device Exemption. News of this approval has been met with a combination of excitement and uncertainty by members of the ALS community. We review the currently available data on the diaphragm pacing system and its use in ALS. Diaphragm pacing appears to be reasonably safe in carefully selected patients, but flaws in the reporting on it thus far preclude conclusions regarding efficacy. Further study is needed.