Abstract Details

Title The Motor Axon Threshold Variability Is Increased in Chronic Inflammatory Demyelinating Polyneuropathy

Topic Neuromuscular and Clinical Neurophysiology (EMG)

Presentation(s) P8 - Poster Session 8 (11:45 AM-12:45 PM)

Poster/Presentation
Number 11-009

Objective To investigate the motor axon threshold variability in chronic inflammatory demyelinating polyneuropathy (CIDP) with axonal loss.

Background Alterations in membrane excitability may precede motor axon degeneration in CIDP. Insights into the nodal Na+ currents may support abnormalities in excitability and can be obtained by quantifying the motor axon threshold variability at motor unit number estimation using its coefficient of variation referred to as the relative spread (RS) of threshold.

Design/Methods Electrophysiological investigations of the median nerve were carried out in CIDP for at least 5 years. We included 20 CIPD patients (mean age 65) that had chronic partial denervation with reinnervation of the abductor pollicis brevis (APB) muscle, as indicated by quantitative needle EMG. Following the nerve conduction studies, a detailed stimulus-response curve referred to as a muscle scan (MScan) was obtained by stimulating the median nerve at wrist and recording the CMAP from the APB for at least 500 stimuli with exponentially decreasing intensity. The mean RS of the motor units modelled to account for the MScan was computed offline using a novel machine-learning based optimization referred to as the RSfit. Measurements from 13 age-matched control subjects were used to assess the deviations in patients by Z-scores.

Results The RS was 1.33 % in controls and was increased to 2.3 % (Z=3, t-test p<0.001) in the CIDP group. The CIDP patients also showed a prolongation of the CMAP latency (Z=4.9) and a reduction of the log-transformed CMAP amplitude (Z=-2.1) whereas the CMAP threshold current did not appear significantly increased (Z=1).

Conclusions We found that the RS was increased in the CIDP patients with axonal loss, consistent with an increase in the nodal Na+ current. Our data suggest that the “Na+ mediated axonal degeneration” contributes to the CIDP pathophysiology, as described in hereditary demyelinating polyneuropathies.

Authors/Disclosures
Christian Krarup, MD, DMSc, FRcP, FAAN (Rigshospitalet) PRESENTER	Dr. Krarup has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for Shire/Takeda. Dr. Krarup has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Shire/Takeda. Dr. Krarup has received publishing royalties from a publication relating to health care.
Ali Al-Zuhairy, MD, PhD	Dr. Al-Zuhairy has nothing to disclose.
Johannes Jakobsen, MD, DMSci	The institution of Dr. Jakobsen has received research support from TAKEDA. Dr. Jakobsen has received publishing royalties from a publication relating to health care. Dr. Jakobsen has received personal compensation in the range of $5,000-$9,999 for serving as a Advisor with Danish Medicine Counsil.
	No disclosure on file

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