Acute retigabine-induced effects on myelinated motor axons in amyotrophic lateral sclerosis.

Altered motor neuron excitability in patients with amyotrophic lateral sclerosis (ALS) has been suggested to be an early pathophysiological mechanism associated with motor neuron death. Compounds that affect membrane excitability may therefore have disease-modifying effects. Through which mechanism(s), these compounds modulate membrane excitability is mostly provided by preclinical studies, yet remains challenging to verify in clinical studies.

Motor unit integrity in multifocal motor neuropathy: A systematic evaluation with CMAP scans.

Introduction/aims: Progressive axonal loss in multifocal motor neuropathy (MMN) is often assessed with nerve conduction studies (NCS), by recording maximum compound muscle action potentials (CMAPs). However, reinnervation maintains the CMAP amplitude until a significant portion of the motor unit (MU) pool is lost. Therefore, we performed more informative CMAP scans to study MU characteristics in a large cohort of patients with MMN.

Excitability of motor and sensory axons in multifocal motor neuropathy.

Objective: To assess excitability differences between motor and sensory axons of affected nerves in patients with multifocal motor neuropathy (MMN).

Methods: We performed motor and sensory excitability tests in affected median nerves of 20 MMN patients and in 20 age-matched normal subjects. CMAPs were recorded from the thenar and SNAPs from the 3rd digit.

Simulating perinodal changes observed in immune-mediated neuropathies: impact on conduction in a model of myelinated motor and sensory axons.

Immune-mediated neuropathies affect myelinated axons, resulting in conduction slowing or block that may affect motor and sensory axons differently. The underlying mechanisms of these neuropathies are not well understood. Using a myelinated axon model, we studied the impact of perinodal changes on conduction.

Warming nerves for excitability testing.

Introduction: The aim of this study was to find the best method of warming the median nerve before excitability testing to a standard temperature.

Methods: In 5 healthy subjects, the forearm and hand were warmed for 1 h to 37°C by infrared lamp, water blanket, or water bath. Recordings were performed before and during warming every 10 min.

Excitability tests using high-density surface-EMG: A novel approach to studying single motor units.

Objective: To study excitability of single motor units (MUs) using high-density surface-EMG.

Methods: Motor unit action potentials (MUAPs) were evoked by submaximal stimulation of the median nerve at the wrist and recorded with a 9 × 14 electrode grid on the skin overlying the thenar muscles. For excitability tests of single MUs, the most optimal specific single-channel surface-EMG signal was selected based on the spatiotemporal profile of single MUs.

Acute Effects of Riluzole and Retigabine on Axonal Excitability in Patients With Amyotrophic Lateral Sclerosis: A Randomized, Double-Blind, Placebo-Controlled, Crossover Trial.

Increased excitability of motor neurons in patients with amyotrophic lateral sclerosis (ALS) may be a relevant factor leading to motor neuron damage. This randomized, double-blind, three-way crossover, placebo-controlled study evaluated peripheral motor nerve excitability testing as a biomarker of hyperexcitability and assessed the effects of riluzole and retigabine in 18 patients with ALS. We performed excitability testing at baseline, and twice after participants had received a single dose of either 100 mg riluzole, 300 mg retigabine, or placebo.

Sodium-potassium pump assessment by submaximal electrical nerve stimulation.

Objective: Sodium-potassium pump dysfunction in peripheral nerve is usually assessed by determining axonal hyperpolarization following maximal voluntary contraction (MVC) or maximal electrical nerve stimulation. As MVC may be unreliable and maximal electrical stimulation too painful, we assessed if hyperpolarization can also be induced by submaximal electrical nerve stimulation.

Methods: In 8 healthy volunteers different submaximal electrical stimulus trains were given to the median nerve at the wrist, followed by 5 min assessment of thresholds for compound muscle action potentials of 20%, 40% or 60% of maximal.

Comparing excitability at 37°C versus at 20°C: Differences between motor and sensory axons.

Introduction: In some peripheral nervous system disorders, cold induces symptoms of muscle weakness without loss of sensation. To understand this selective effect on motor function, it is first essential to delineate the effects of cooling in motor and sensory axons of healthy subjects.

Methods: In 17 healthy volunteers, we performed excitability and clinical tests of median nerve motor and sensory axons at 37°C and at 20°C.