Supramaximal Stimulus Intensity as a Diagnostic Tool in Chronic Demyelinating Neuropathy

Vivien Parker; Jodi Warman Chardon; Julie Mills; Claire Goldsmith; Pierre R Bourque

doi:10.1155/2016/6796270

Supramaximal Stimulus Intensity as a Diagnostic Tool in Chronic Demyelinating Neuropathy

Neurosci J. 2016:2016:6796270. doi: 10.1155/2016/6796270. Epub 2016 Jun 16.

Authors

Vivien Parker¹, Jodi Warman Chardon², Julie Mills³, Claire Goldsmith⁴, Pierre R Bourque⁵

Affiliations

¹ Division of Neurology, University of Ottawa, Ottawa, ON, Canada K1Y 4E9.
² Division of Neurology, University of Ottawa, Ottawa, ON, Canada K1Y 4E9; Ottawa Hospital Research Institute, Ottawa, ON, Canada K1Y 4E9; Department of Genetics, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada K1H 8L1.
³ Diagnostic Imaging, The Ottawa Hospital, Ottawa, ON, Canada K1Y 4E9.
⁴ Department of Genetics, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada K1H 8L1.
⁵ Division of Neurology, University of Ottawa, Ottawa, ON, Canada K1Y 4E9; Ottawa Hospital Research Institute, Ottawa, ON, Canada K1Y 4E9.

Abstract

Objective. The ability to correctly identify chronic demyelinating neuropathy can have important therapeutic and prognostic significance. The stimulus intensity value required to obtain a supramaximal compound muscle action potential amplitude is a commonly acquired data point that has not been formally assessed as a diagnostic tool in routine nerve conduction studies to identify chronic neuropathies. We postulated that this value was significantly elevated in chronic demyelinating neuropathy. Methods. We retrospectively reviewed electrophysiology laboratory records to compare the stimulus intensity values recorded during median and ulnar motor nerve conduction studies. The groups studied included normal controls (n = 42) and the following diagnostic categories: chronic inflammatory demyelinating neuropathy (CIDP) (n = 20), acquired inflammatory demyelinating neuropathy (AIDP) (n = 13), Charcot Marie Tooth (CMT) type 1 or 4C (n = 15), carpal tunnel syndrome (CTS) (n = 11), and amyotrophic lateral sclerosis (ALS) (n = 18). Results. Supramaximal intensities were significantly higher in patients with CMT (median nerve: 43.4 mA) and CIDP (median nerve: 38.9 mA), whereas values similar to normal controls (median nerve: 25.3 mA) were obtained in ALS, CTS, and AIDP. Conclusions. Supramaximal stimulus intensity may be used as an additional criterion to identify the pathophysiology of neuropathy. We postulate that endoneurial hypertrophic changes may increase electrical impedance and thus the threshold of excitation at nodes of Ranvier.