Excitability properties of median and peroneal motor axons

Kuwabara, Satoshi; Cappelen‐Smith, Cecilia; Lin, Cindy S.‐Y.; Mogyoros, Ilona; Bostock, Hugh; Burke, David

doi:10.1002/1097-4598(200009)23:9<1365::aid-mus7>3.3.co;2-t

Cited by 22 publications

(40 citation statements)

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“…The preferential localization of demyelination in the nerves of the arms may explain the greater improvement in muscle strength in the arms compared to the legs following IVIg treatment in MMN. These differences in findings prompt the suggestion that nerves of the arms are more vulnerable to demyelination, and nerves of the legs more vulnerable to axonal loss [103]. The results of our long-term IVIg maintenance treatment study further support different disease mechanisms in nerves of the arms and legs [104].…”

Section: Multifocal Motor Neuropathysupporting

confidence: 72%

The spectrum of lower motor neuron syndromes

Berg-Vos

Berg

Visser

et al. 2003

Journal of Neurology

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This review discusses the most important lower motor neuron syndromes. This relatively rare group of syndromes has not been well described clinically. Two subgroups can be distinguished: patients in whom motor neurons (lower motor neuron disease (LMND)) are primarily affected or motor axons and their surrounding myelin (multifocal motor neuropathy (MMN)), both leading to muscle atrophy and weakness. Both hereditary and sporadic forms of LMND have been described. The discussion of recent advances in the genetic knowledge of several hereditary forms of LMND may lead to a better understanding of the pathophysiology and the development of therapeutic strategies. By contrast, the pathogenesis of sporadic LMND is largely unknown. It is, therefore, difficult to consider the various sporadic forms of LMND, discussed in this review, as separate diseases. Because the diagnostic and therapeutic options may differ, it would seem rational to consider sporadic LMND as a spectrum of syndromes which can be distinguished from each other on the basis of clinical presentation.MMN is a lower motor neuron syndrome with presumed immunemediated pathogenesis. Evidence of motor conduction block on nerve conduction studies and a positive response to treatment with intravenous immunoglobulins (IVIg) are considered the most relevant criteria for the diagnosis of MMN. As it is treatable, it is important to distinguish MMN from LMND. Careful electrophysiological analysis in the search for conduction block is, therefore, required in all adult patients with pure lower motor neuron syndromes. For the individual patient, distinction between the various lower motor neuron syndromes is important as it enables the physician to provide adequate information over the disease course in LMND and to facilitate early treatment in MMN.

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Section: Multifocal Motor Neuropathysupporting

confidence: 72%

The spectrum of lower motor neuron syndromes

Berg-Vos

Berg

Visser

et al. 2003

Journal of Neurology

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“…However, the excitability parameters that depend most on slow K + channels—namely, the late subnormal phase in the recovery cycle, the accommodation that occurs with depolarisation during threshold electrotonus, and the undershoot in excitability that follows31—were within the normal range and on average significantly greater in the patients with aNMT than in the age matched control group. These changes, which suggest a relative up regulation of slow K + channels in these patients, could not account for the ectopic discharges.…”

Section: Discussionmentioning

confidence: 91%

“…These abnormalities in the overshooting of electrical excitability after a displacement of membrane potential, whether by a spike or by applied currents, are illustrated in fig 4. Apart from these three, the only other parameter of the 22 tested that differed significantly (p<0.01) between the patients with aNMT and matched controls was S2 accommodation,31 measured from the depolarising threshold electrotonus curve by subtracting the plateau level at 90–100 ms from the peak threshold reduction. This quantity, which depends in part, as do the excitability overshoots, on slow potassium conductance, averaged 29.9 (1.1)% in the patients with aNMT and 24.5 (0.7)% in the age matched controls (p=0.001).…”

Section: Resultsmentioning

confidence: 99%

Excitability properties of motor axons in patients with spontaneous motor unit activity

Kiernan

Hart²,

Bostock³

2001

Journal of Neurology, Neurosurgery &Amp; Psychiatry

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Objectives-Measures of nerve excitability provide information about biophysical properties of peripheral axons in disease states. One measure, the strength duration time constant ( SD ), was previously reported to be prolonged in motor axons of patients with acquired neuromyotonia. The present study used a new protocol that applies a more comprehensive and sensitive panel of measures of axonal excitability, to determine firstly whether changes in SD were present in a group of patients with evidence of spontaneous motor unit activity; and secondly, if such changes in SD were present, whether other parameters of axonal excitability were aVected, to clarify the mechanism of the change in SD . Methods-Eleven patients with both symptoms and EMG evidence of spontaneous motor unit activity were studied. Eight patients had autoimmune associated acquired neuromyotonia (aNMT) and three had the cramp fasciculation syndrome. The protocol first measured stimulus-response behaviour using two stimulus durations (from which the distribution of strength-duration time constants was estimated), and then threshold tracking was used to determine threshold electrotonus to 100 ms polarising currents, a current-threshold relation (indicating inward and outward rectification), and the recovery of excitability after supramaximal activation. Results-The results were compared with previously published normal data. The value for SD of motor axons in the patient group was 0.43 (0.02) ms (mean (SEM)), identical with the control value. Most other indices of axonal excitability, including those dependent on fast potassium channels, were also found to be normal. When compared with age matched controls however, the patients with acquired neuromyotonia had significantly greater late subexcitability after an impulse, greater excitability overshoots after depolarisation or hyperpolarisation, and more accommodation. Conclusions-No clear evidence for the mechanism of ectopic discharge in these patients was obtained, probably because the activity was generated focally, and most often at the motor nerve terminals. The unexpected finding of increased excitability overshoots and accommodation compared with age matched controls, suggests a relative up regulation of slow potassium conductance, possibly as a consequence of the continuous motor unit activity. (J Neurol Neurosurg Psychiatry 2001;70:56-64)

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“…One of the possible explanations for this is that motor axons in the arm nerves have slower potassium conductance than motor axons in leg nerves 21 . These differences could contribute to the greater susceptibility of arm motor axons for developing CB 15,21,22 . In line with this results we found CBs in all patients included in the study at sites distinct from common entrapment syndromes, most frequently in radial nerve.…”

Section: Discussionmentioning

confidence: 99%