Impact of carpal tunnel syndrome on ulnar nerve at wrist: Systematic review

Considerable debate exists in the literature about possible anomalies of ulnar nerve at wrist in carpal tunnel syndrome (CTS). We systematically reviewed the literature about electrophysiologic and morphologic changes of ulnar nerve at wrist in CTS. We carried out a comprehensive search using PubMed from 1963 through October 2017. Data were extracted and the quality of the included studies was evaluated. Twenty-eight studies were selected. Seventy-nine percent of the studies report abnormalities of the ulnar nerve conduction. There was a relation between the median and ulnar nerve conduction in almost all the papers, i.e., conduction impairment of the ulnar nerve increased with increasing severity of median nerve involvement, emerging as a process correlated with damage of the median nerve. Seventy-five percent of ultrasonographic studies report changes of ulnar nerve cross sectional area in CTS. Morphologic and functional changes of the ulnar nerve and/or Guyon canal are reported by 100% of papers addressed to this topic. Several papers quoted in this review have some flaws. The key message of present review is that electrophysiological and morphological changes of the ulnar nerve at the wrist can occur in CTS, although the possibility of an overestimation of the phenomenon needs to be considered.