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FC28.3 Changes in nerve excitability properties near the motor nerve terminals in amyotrophic lateral sclerosis
S86
Oral Communications / Clinical Neurophysiology 117 (2006) S49–S111
FC28.2 Mechanisms of cold paralysis assessed by excitability recording H. Franssen, J.T. Van Asseldonk, T. Gebbink, L.H. Van den Berg, L.H. Van Schelven University Medical Center Utrecht, Department of Neurology, The Netherlands Background: Weakness after cooling (cold paralysis) was suggested in multifocal motor neuropathy (MMN). The following mechanism for cold paralysis was proposed: in axons which are depolarized due to inflammation and energy depletion of the Na/K pump, cooling may induce further pump slowing and depolarization (as all enzymes slow down with cooling) yielding depolarizing conduction block. Aim: To study whether cooling in normal axons induces depolarization. Methods: Ten normal subjects were investigated. At temperatures of 37, 25, 20, and 15 °C, we recorded excitability in the median nerve at the wrist, pulsed Doppler peak systolic velocity of the ulnar artery at the wrist and force of the thenar muscle. Results: Excitability recordings showed that cooling yielded progressive fanning in of threshold electrotonus waveforms, steepening of the current–voltage relation, increase of chronaxie, and refractory period, and decrease of supernormality. Peak systolic velocity and muscle force decreased with cooling. The excitability changes are consistent with progressive axonal depolarization during cooling. Possible mechanisms are energy depletion of the pump due to cooling induced vasoconstriction and ischemia, or temperature related pump slowing. To distinguish between these possibilities, we performed a further experiment at 37 °C. A cuff around the upper arm was inflated until the peak systolic velocity had the value that was previously recorded at 15 °C. Excitability recordings showed no evidence of depolarization. Thus, the depolarization at lower temperatures could not be explained by ischemia due to vasoconstriction. Conclusion: Cooling may induce axonal depolarization due to temperature induced slowing of the Na/K pump. This mechanism may explain the reported cold paralysis in MMN patients. A recently conducted questionnaire by our group indicated that MMN patients indeed complain more frequently of cold paralysis than others. doi:10.1016/j.clinph.2006.06.093
FC28.3 Changes in nerve excitability properties near the motor nerve terminals in amyotrophic lateral sclerosis S. Misawa, S. Kuwabara, M. Nakata, K. Kanai, S. Sawai, N. Tamura, T. Hattori Chiba University School of Medicine, Department of Neurology, Japan
Background: Previous axonal excitability studies in amyotrophic lateral sclerosis (ALS) suggested that axonal potassium channel function is impaired in ALS, and this could be responsible for the generation of fasciculations. However, the ectopic activity usually arises from the motor nerve terminals. Objective: To investigate whether dysfunction of potassium channels is predominant in the most distal parts of axons in ALS. Methods: Threshold electrotonus was used to compare accommodation mediated by potassium currents at the motor point of abductor pollicis brevis, and at the wrist portion of the median nerve in 22 patients with ALS and 19 normal subjects. For motor point stimulation, movement-related potentials recorded with an accelerometer were used as target responses. Results: ALS patient showed greater threshold changes to depolarizing conditioning currents at both the motor point and wrist than normal controls, suggesting less accommodation by potassium currents. Differences in the threshold changes in the depolarizing direction between the normal and ALS groups were more prominent at the motor point than at the wrist. Conclusion: In ALS, axonal potassium channels are impaired more prominently near the motor nerve terminals than at the nerve trunk, and this is consistent with evidence that fasciculations arise from the nerve terminals. doi:10.1016/j.clinph.2006.06.094
FC28.4 Changes in axonal excitability following intravenous immunoglobulin infusions in patients with dysimmune demyelinating neuropathy D. Boe¨rio 1, A. Cre´ange 2, J.Y. Hogrel 3, J.P. Lefaucheur 1 1 2 3
Henri Mondor Hospital, Physiology, France Henri Mondor Hospital, Neurology, France Pitie´-Salpeˆtrie`re Hospital, Institut de Myologie, France
Background: Dysimmune demyelinating neuropathies can be associated with significant changes in nerve excitability. Various neurophysiological methods, including the recovery cycle of excitability, stimulus/response (S/R) and strength/duration (S/D) curves reflect axon membrane properties. Aim: To investigate the effects of intravenous immunoglobulin (IVIg) infusions on nerve excitability in patients with multifocal motor neuropathy (MMN) with persistent conduction blocks or chronic inflammatory demyelinating polyneuropathy (CIDP). Methods: Sixteen patients (9 MMN, 7 CIDP) were evaluated before and after IVIgs for five consecutive days (0.4 g/kg/day). Absolute refractory period (ARP) duration was estimated using double collision technique. Paired pulses provided relative refractory period
Oral Communications / Clinical Neurophysiology 117 (2006) S49–S111
FC28.2 Mechanisms of cold paralysis assessed by excitability recording H. Franssen, J.T. Van Asseldonk, T. Gebbink, L.H. Van den Berg, L.H. Van Schelven University Medical Center Utrecht, Department of Neurology, The Netherlands Background: Weakness after cooling (cold paralysis) was suggested in multifocal motor neuropathy (MMN). The following mechanism for cold paralysis was proposed: in axons which are depolarized due to inflammation and energy depletion of the Na/K pump, cooling may induce further pump slowing and depolarization (as all enzymes slow down with cooling) yielding depolarizing conduction block. Aim: To study whether cooling in normal axons induces depolarization. Methods: Ten normal subjects were investigated. At temperatures of 37, 25, 20, and 15 °C, we recorded excitability in the median nerve at the wrist, pulsed Doppler peak systolic velocity of the ulnar artery at the wrist and force of the thenar muscle. Results: Excitability recordings showed that cooling yielded progressive fanning in of threshold electrotonus waveforms, steepening of the current–voltage relation, increase of chronaxie, and refractory period, and decrease of supernormality. Peak systolic velocity and muscle force decreased with cooling. The excitability changes are consistent with progressive axonal depolarization during cooling. Possible mechanisms are energy depletion of the pump due to cooling induced vasoconstriction and ischemia, or temperature related pump slowing. To distinguish between these possibilities, we performed a further experiment at 37 °C. A cuff around the upper arm was inflated until the peak systolic velocity had the value that was previously recorded at 15 °C. Excitability recordings showed no evidence of depolarization. Thus, the depolarization at lower temperatures could not be explained by ischemia due to vasoconstriction. Conclusion: Cooling may induce axonal depolarization due to temperature induced slowing of the Na/K pump. This mechanism may explain the reported cold paralysis in MMN patients. A recently conducted questionnaire by our group indicated that MMN patients indeed complain more frequently of cold paralysis than others. doi:10.1016/j.clinph.2006.06.093
FC28.3 Changes in nerve excitability properties near the motor nerve terminals in amyotrophic lateral sclerosis S. Misawa, S. Kuwabara, M. Nakata, K. Kanai, S. Sawai, N. Tamura, T. Hattori Chiba University School of Medicine, Department of Neurology, Japan
Background: Previous axonal excitability studies in amyotrophic lateral sclerosis (ALS) suggested that axonal potassium channel function is impaired in ALS, and this could be responsible for the generation of fasciculations. However, the ectopic activity usually arises from the motor nerve terminals. Objective: To investigate whether dysfunction of potassium channels is predominant in the most distal parts of axons in ALS. Methods: Threshold electrotonus was used to compare accommodation mediated by potassium currents at the motor point of abductor pollicis brevis, and at the wrist portion of the median nerve in 22 patients with ALS and 19 normal subjects. For motor point stimulation, movement-related potentials recorded with an accelerometer were used as target responses. Results: ALS patient showed greater threshold changes to depolarizing conditioning currents at both the motor point and wrist than normal controls, suggesting less accommodation by potassium currents. Differences in the threshold changes in the depolarizing direction between the normal and ALS groups were more prominent at the motor point than at the wrist. Conclusion: In ALS, axonal potassium channels are impaired more prominently near the motor nerve terminals than at the nerve trunk, and this is consistent with evidence that fasciculations arise from the nerve terminals. doi:10.1016/j.clinph.2006.06.094
FC28.4 Changes in axonal excitability following intravenous immunoglobulin infusions in patients with dysimmune demyelinating neuropathy D. Boe¨rio 1, A. Cre´ange 2, J.Y. Hogrel 3, J.P. Lefaucheur 1 1 2 3
Henri Mondor Hospital, Physiology, France Henri Mondor Hospital, Neurology, France Pitie´-Salpeˆtrie`re Hospital, Institut de Myologie, France
Background: Dysimmune demyelinating neuropathies can be associated with significant changes in nerve excitability. Various neurophysiological methods, including the recovery cycle of excitability, stimulus/response (S/R) and strength/duration (S/D) curves reflect axon membrane properties. Aim: To investigate the effects of intravenous immunoglobulin (IVIg) infusions on nerve excitability in patients with multifocal motor neuropathy (MMN) with persistent conduction blocks or chronic inflammatory demyelinating polyneuropathy (CIDP). Methods: Sixteen patients (9 MMN, 7 CIDP) were evaluated before and after IVIgs for five consecutive days (0.4 g/kg/day). Absolute refractory period (ARP) duration was estimated using double collision technique. Paired pulses provided relative refractory period