The recovery cycle of excitability assessed by a conventional electrodiagnostic machine: A study in healthy volunteers and in Charcot-Marie-Tooth 1A patients.

OBJECTIVE

To validate the 'paired pulses' technique with a conventional electrodiagnostic machine (CEM) for studying the axonal excitability recovery cycle (ERC).

METHODS

Paired pulses, with a variable inter-stimulus interval, were delivered at the wrist along the median nerve. The CEM repeatability was verified in a group of 15 healthy volunteers (test/retest analysis). ERC was then applied in 40 healthy volunteers and 10 patients with Charcot-Marie-Tooth type 1A (CMT1A), using both the threshold tracking (TT) reference method and CEM (basal condition, during and after ischemia).

RESULTS

CEM parameters evaluating absolute refractory and supernormal periods were reproducible (interclass correlation coefficient > 0.75). CEM results were consistent with TT method and literature data. In CMT1A, refractory and superexcitable periods were significantly reduced. According to receiving operator characteristic analysis, the CEM supernormal period area was the most relevant parameter for discriminating CMT1A from healthy volunteers (area under the curve = 0.98).

CONCLUSIONS

CEM was a valid procedure for studying ERC. CMT1A patients exhibited ERC alterations due to modifications in passive membrane properties and of nodal ion channel distribution resulting from demyelination.

SIGNIFICANCE: Studying ERC with CEM could be performed in routine practice in patients with peripheral neuropathies to provide information on motor axonal excitability.