A study of retrograde degeneration of median nerve forearm segment in carpal tunnel syndrome of variable severities

Abstract

Introduction: Carpal tunnel syndrome (CTS) is a disorder of the hand which results from compression of the median nerve within its fibro-osseous tunnel at the wrist. The slowing in the forearm motor conduction velocity suggests the presence of retrograde degeneration. Existing studies conflict regarding a correlation between the severities of the entrapment neuropathy in CTS and slowing of median motor nerve conduction velocity in the forearm.
Aims: The objective of this work was to study retrograde degeneration (RGD) of the median nerve forearm segment in patients with CTS and its relation to variable severity of CTS in Egyptian patients.
Patients and methods: Twenty-four patients with CTS were included in this study. The Forearm mixed nerve conduction is presumed to be indicative of the conduction of the median nerve over the forearm and is used widely to assess the causes of slowing forearm conduction velocity in CTS. In addition to conventional nerve conduction studies of the upper limb, forearm median mixed conduction studies were performed. Median motor forearm amplitudes and nerve conduction velocities (NCVs) as well as forearm median mixed amplitudes and NCVs were considered as parameters of RGD. 
Results: There were statistically significant differences as regards forearm mixed nerve action potential (MNAP) amplitude and median motor amplitude in the forearm segment but there were no statistically significant differences as regards forearm median mixed peak latency and NCV. There was no statistically significant relation between grades of severities of CTS in the studied hands and both forearm median motor NCV and forearm MNAP amplitude using Monte Carlo test (MCp = 0.323 and 0.464).
Conclusions: Retrograde degeneration exists in patients with CTS. Forearm median motor NCV and median mixed conduction study are valid electrophysiologic tools for the assessment of RGD in patients with CTS. Retrograde degeneration is not related to grade of severity of CTS.

KEYWORDS Carpal tunnel syndrome; Electrodiagnosis; Forearm median mixed study; Retrograde degeneration