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.

Case 9

Ulnar nerve lesions are the second most common mononeuropathies encountered in clinical practice. Although the majority of the lesions are due to entrapment/compression of the ulnar nerve around the elbow (at the cubital tunnel or ulnar groove), it is important to consider and exclude distal ulnar nerve lesions at the wrist or palm. This case highlights the clinical and electrodiagnostic findings of ulnar neuropathies at the wrist, including Guyon canal and pisohamate hiatus. It also discusses the electrodiagnostic challenges in distinguishing distal from proximal ulnar nerve lesions. Emphasis is placed on the use of additional studies, such as the dorsal ulnar sensory nerve action potential, first dorsal interosseous recording, inching studies, and palm stimulation, in the accurate diagnosis of ulnar nerve lesions at the wrist.

Case 15

Ulnar nerve lesions are the second most common mononeuropathies encountered in clinical practice. The majority of ulnar neuropathies are across the elbow, more specifically due to entrapment or compression of the ulnar nerve at the cubital tunnel or ulnar groove. This case highlights the clinical and electrodiagnostic findings of ulnar neuropathies across the elbow and discusses the challenges in making an accurate diagnosis. Focal slowing of conduction velocities and/or conduction block are the main findings that pinpoint the site of the lesion, while the needle electromyography is poor in accurate localization, mostly due to the limited number of ulnar innervated muscles in the forearm. Important additional testing that often is recommended to aid in the accurate diagnosis of ulnar nerve lesions across the elbow includes the dorsal ulnar sensory nerve action potential, ulnar motor conduction study recording the first dorsal interosseous, and inching studies across the elbow.