Median-to-Ulnar Nerve Communication in Carpal Tunnel Syndrome: An Electrophysiological Study

Abstract

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.

Motor Conduction Studies and Handgrip in Hereditary TTR Amyloidosis: Simple Tools to Evaluate the Upper Limbs

“…This result might be explained by the high prevalence of CTS in the dominant hand (more often right) of the general population, because the controls also presented a similar mean right CMAP amplitude of the median nerve. Moreover, when present, CTS in ATTRv is usually bilateral, underlining the importance of detecting left (non-dominant) or bilateral CTS in ATTRv as a specific finding of amyloidosis, less often encountered in routine NCS ( 2 , 12 ). Indeed, while bilateral CTS is an early sign of ATTRv, CTS in the dominant hand is the rule in general population, especially in the elderly ( 20 ).…”

“…Nerve conduction studies (NCSs) were performed on both median nerves for all the subjects enrolled according to standard procedures (i.e., bipolar surface stimulating electrodes delivering rectangular pulses 0.1–0.5 ms in duration and recording electrodes placed over the recording site with a ground electrode placed between recording and stimulation electrodes) ( 12 ). The stimulation of the right and left median nerve was performed at wrist and elbow and recording from APB.…”

Efficacy of 5% Dextrose Water Injection for Peripheral Entrapment Neuropathy: A Narrative Review

“…Nevertheless, the electrophysiological study presented a limited diagnosis of CTS with varied sensitivity (56% to 85%) and specificity (94% to 96%) [48,49]. For example, Martin-Gruber anastomoses may lead to misinterpretation or erroneous results during routine nerve conduction studies in patients with CTS [50]. Hence, underestimation of CTS severity may be attributed to the failure in proficient diagnosis.…”

Does Recurrence of Carpal Tunnel Syndrome (CTS) after Complete Division of the Transverse Ligament Really Exist?

“…Amyloid deposits in the transverse carpal ligament have also been observed in recurrent CTS [ 13 , 14 , 15 ]. Anatomic innovation variants such as the median-ulnar junction (MUC) branch, also known as the Martin-Gruber anastomosis, can lead to interpretation errors in nerve conduction studies of patients with carpal tunnel syndrome [ 16 ]. As early as 1998, Rempel et al stated that case definitions that included electrodiagnostic examination results are of a higher specificity than case definitions that did not include electrodiagnostic examinations.…”

“…Amyloid deposits in the transverse carpal ligament have also been observed in recurrent CTS [13][14][15]. Anatomic innovation variants such as the median-ulnar junction (MUC) branch, also known as the Martin-Gruber anastomosis, can lead to interpretation errors in nerve conduction studies of patients with carpal tunnel syndrome [16].…”