A model incorporating ultrasound to predict the probability of fast disease progression in amyotrophic lateral sclerosis

Neurophysiological and imaging biomarkers of lower motor neuron dysfunction in motor neuron diseases/amyotrophic lateral sclerosis: IFCN handbook chapter

This chapter discusses comprehensive neurophysiological biomarkers utilised in motor neuron disease (MND) and, in particular, its commonest form, amyotrophic lateral sclerosis (ALS). These encompass the conventional techniques including nerve conduction studies (NCS), needle and high-density surface electromyography (EMG) and H-reflex studies as well as novel techniques. In the last two decades, new methods of assessing the loss of motor units in a muscle have been developed, that are more convenient than earlier methods of motor unit number estimation (MUNE),and may use either electrical stimulation (e.g. MScanFit MUNE) or voluntary activation (MUNIX). Electrical impedance myography (EIM) is another novel approach for the evaluation that relies upon the application and measurement of high-frequency, low-intensity electrical current. Nerve excitability techniques (NET) also provide insights into the function of an axon and reflect the changes in resting membrane potential, ion channel dysfunction and the structural integrity of the axon and myelin sheath. Furthermore, imaging ultrasound techniques as well as magnetic resonance imaging are capable of detecting the constituents of morphological changes in the nerve and muscle. The chapter provides a critical description of the ability of each technique to provide neurophysiological insight into the complex pathophysiology of MND/ALS. However, it is important to recognise the strengths and limitations of each approach in order to clarify utility. These neurophysiological biomarkers have demonstrated reliability, specificity and provide additional information to validate and assess lower motor neuron dysfunction. Their use has expanded the knowledge about MND/ALS and enhanced our understanding of the relationship between motor units, axons, reflexes and other neural circuits in relation to clinical features of patients with MND/ALS at different stages of the disease. Taken together, the ultimate goal is to aid early diagnosis, distinguish potential disease mimics, monitor and stage disease progression, quantify response to treatment and develop potential therapeutic interventions.

Ultrasonic detection of vagus, accessory, and phrenic nerve atrophy in amyotrophic lateral sclerosis: Relation to impairment and mortality

BACKGROUND AND PURPOSE

In amyotrophic lateral sclerosis (ALS), phrenic nerve (PN) atrophy has been found, whereas there is controversy regarding vagus nerve (VN) atrophy. Here, we aimed to find out whether PN atrophy is related to respiratory function and 12-month survival. Moreover, we investigated the relevance of VN and spinal accessory nerve (AN) atrophy in ALS.

METHODS

This prospective observational monocentric study included 80 adult participants (40 ALS patients, 40 age- and sex-matched controls). The cross-sectional area (CSA) of bilateral cervical VN, AN, and PN was measured on high-resolution ultrasonography. Clinical assessments included the Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R), the Non-Motor Symptoms Questionnaire, and handheld spirometry of forced vital capacity (FVC). One-year survival was documented.

RESULTS

The CSA of each nerve, VN, AN, and PN, was smaller in ALS patients compared to controls. VN atrophy was unrelated to nonmotor symptom scores. PN CSA correlated with the respiratory subscore of the ALSFRS-R (Spearman test, r = 0.59, p < 0.001), the supine FVC (r = 0.71, p < 0.001), and the relative change of sitting-supine FVC (r = -0.64, p = 0.001). Respiratory impairment was predicted by bilateral mean PN CSA (p = 0.046, optimum cutoff value of ≤0.37 mm2 , sensitivity = 92%, specificity = 56%) and by the sum of PN and AN CSA (p = 0.036). The combination of ALSFRS-R score with PN and AN CSA measures predicted 1-year survival with similar accuracy as the combination of ALSFRS-R score and FVC.

CONCLUSIONS

Ultrasonography detects degeneration of cranial nerve motor fibers. PN and AN calibers are tightly related to respiratory function and 1-year survival in ALS.

Nerve excitability measured with the TROND protocol in amyotrophic lateral sclerosis: a systematic review and meta-analysis

This meta-analysis assessed the 30+ nerve excitability indices generated by the TROND protocol to identify potential biomarkers for amyotrophic lateral sclerosis (ALS). A comprehensive search was conducted in multiple databases to identify human studies that tested median motor axons. Forest plot analyses were performed using a random-effects model to determine the pooled effect (Z-score), heterogeneity (I2), and Cohen's d for potential biomarker identification. Out of 2,866 studies, 23 studies met the inclusion criteria, incorporating data from 719 controls and 942 patients with ALS. Seven indices emerged as potential biomarkers: depolarizing threshold electrotonus (TEd) 90-100 ms, strength-duration time constant (SDTC), superexcitability, TEd 40-60 ms, resting I/V slope, 50% depolarizing I/V, and subexcitability (ranked by the magnitude of the difference between patients and controls from largest to smallest). In a sensitivity analysis focusing on patients with larger compound muscle action potentials (CMAPs), only four indices were potential biomarkers: TEd 10-20 ms, TEd 90-100 ms, superexcitability, and SDTC. Among the extensive range of 30+ excitability indices generated by the TROND protocol, we have identified seven indices that effectively differentiate patients with ALS from healthy controls. Furthermore, a smaller subset of four indices shows promise as potential biomarkers when the CMAP remains relatively large. However, most studies were considered to be at moderate risk of bias due to case-control designs and absence of sensitivity and specificity calculations, underscoring the need for more prospective diagnostic test-accuracy studies with appropriate disease controls.NEW & NOTEWORTHY This meta-analysis uncovers seven potential axonal excitability biomarkers for lower motor neuron pathology in ALS, shedding light on ion channel dysfunction. The identified dysfunction aligns with the primary pathology-protein homeostasis disruption. These biomarkers could fill a gap to detect presymptomatic spread of the disease in the spinal cord and monitor treatments targeting protein homeostasis and limiting spread, toward enhancing patient care.