Median-to-ulnar nerve communication in carpal tunnel syndrome: An electrophysiological study

The median-to-ulnar communicating branch (MUC) is an asymptomatic variant of the upper limb innervation that can lead to interpretation errors in routine nerve conduction studies. The diagnosis of carpal tunnel syndrome (CTS) or ulnar nerve lesions can be complicated by the presence of MUC. In this study, we describe electrophysiological features of MUC in CTS patients presenting to our clinic. We enrolled MUB cases from consecutive CTS patients referred to our laboratory between the years 2014 and 2019. MUC was present in 53 limbs (36 patients) from the studied population. MUC was bilateral in 53% of patients. MUC type II was the most common subtype (74%), followed by types III and I; more coexisting MUC types were found in the majority of tested limbs. A positive correlation was demonstrated between the severity of CTS and the presence of positive onset, faster CV, or a double component of the compound muscle action potentials. We emphasize the importance of suspecting the presence of MUC in CTS in the presence of a positive onset or a double component in routine motor conduction studies.