Kranthi Mandava1, Anam Shaikh1, Mustafa Jaffry1, Kazim Jaffry1, Muhammed Ors1, Ronak Trivedi1, Iqra Faiz1, Ajay Gandhi1, Tejas Patel1, Abu Nasar1, Ankit Pahwa1, Howard Sander2, Nizar Souayah1
1New Jersey Medical School, 2NYU Grossman School of Medicine
Objective:
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.
Background:
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.
Design/Methods:
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.
Results:
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.
Conclusions:
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.