Motor Nerve Conduction Slowing in Amyotrophic Lateral Sclerosis (P10-8.006)

Abstract

<h3>Objective:</h3> To determine the range of conduction values for motor nerve conduction slowing and further characterize the distribution of conduction slowing in ALS and characterize the limits of conduction slowing beyond which the diagnosis of ALS is uncertain. <h3>Background:</h3> Abnormal motor nerve conduction studies in ALS are attributed to loss of large axons and distal axonopathy, however conduction slowing can be the result of superimposed demyelinating polyneuropathy or an alternate diagnosis. <h3>Design/Methods:</h3> The electrodiagnostic data of 76 chronic inflammatory demyelinating polyneuropathy (CIDP) patients, identified using AAN research criteria was used to create 12 novel equations using regression analysis that determine a range of the expected slowing of a primary demyelinating polyneuropathy. Demyelinating range confidence intervals were defined by assessing conduction velocity (CV), distal latency (DL), and F latency in relation to distal compound muscle action potential (CMAP) amplitude of median, ulnar, fibular, and tibial nerves. Results were then validated in 38 additional CIDP patients. These developed equations were then used to evaluate conduction slowing in 95 patients with ALS. Transformed CMAP amplitude was used as an independent variable whereas transformed DL, CV, and F were used as dependent variables. <h3>Results:</h3> CV slowing, prolonged DL, and abnormal F latency were observed respectively in 22.2%, 19.6%, and 46.7% of the studied nerves. When slowing occurred, it affected more than one segment of the motor nerve, suggesting that loss of large axons is the main mechanism of slowing. No ALS patient had more than 2 nerves with CV slowing in the confidence interval defined by the regression equations or the American Academy of Neurology (AAN) research criteria for CIDP diagnosis. <h3>Conclusions:</h3> The presence of more than two motor nerves with CV slowing in the demyelinating range defined by the regression analysis or AAN criteria in ALS patients suggests an alternative diagnosis or superimposed demyelination. <b>Disclosure:</b> Mr. Mandava has nothing to disclose. Miss Shaikh has nothing to disclose. Mr. Jaffry has nothing to disclose. Mr. Jaffry has nothing to disclose. Mr. Ors has nothing to disclose. Mr. Trivedi has nothing to disclose. Ms. Faiz has nothing to disclose. Mr. Gandhi has nothing to disclose. Dr. Patel has nothing to disclose. Abu Nasar, MD has nothing to disclose. Ankit Pahwa has nothing to disclose. Dr. Sander has received personal compensation for serving as an employee of Grifols. Dr. Sander has received personal compensation in the range of $10,000-$49,999 for serving as a Consultant for Grifols. Dr. Sander has received personal compensation in the range of $10,000-$49,999 for serving as an Expert Witness for Law firm. Dr. Souayah has received publishing royalties from a publication relating to health care.