The purview of multifascicle ulnar nerves in cubital tunnel syndrome: Single‐case sonographic observation

A 35-year-old woman was referred for electrophysiological examination with a likely diagnosis of cubital tunnel syndrome (CuTS). She had complaints of right medial elbow pain and paresthesia for 2 months. The neurological examination revealed a positive Tinel sign over the right cubital tunnel and hypoesthesia in the fourth and fifth fingers of the right hand. Nerve conduction studies were consistent with decreased motor nerve conduction velocity at the right cubital tunnel (normal on the left side). Electromyography was normal. Ultrasonography (US) disclosed mild enlargement of the right ulnar nerve proximal to the cubital tunnel, bifid right ulnar nerve at the tunnel (Fig. 1A), and a left ulnar nerve with four fascicles at the level of the cubital tunnel (Fig. 1B). Cross-sectional area (mm) measurements (proximally, at the tunnel and distally) were as follows: 8.8, 6.6, 7.6 (right side) and 10.4, 9.5, 10.6 (left side), respectively. In the light of the electrophysiologic and sonographic findings, the patient was diagnosed with right-sided CuTS. She was followed conservatively with a nonsteroidal anti-inflammatory drug, static elbow splint, and daily life modifications. She was found to have improved clinically on follow-up 4 weeks later. Anatomic variations of the peripheral nerves (mainly of the median nerve) have been mentioned in the literature. Further, such anomalies have also been linked to the presence of nerve entrapments. However, to the best of our knowledge, a bifid ulnar nerve at the cubital tunnel has not been reported in association with CuTS. An ulnar nerve consisting of four fascicles at the cubital tunnel has also not been described previously. Herein, two issues are worth mentioning and need clarification: (1) What is the reason why both ulnar nerves in our patient showed fascicular divisions only at the cubital tunnel? (not proximally or distally). (2) What is the clinical relevance of these structural variations with regard to entrapment? Significant overuse during flexion and extension of the elbow joint might be one possible mechanism in helping to answer the first question. However, this speculation should be investigated in individuals of different ages and with varying cumulative elbow use. On the other hand, in view of our patient’s findings, nerve thickness/number of fascicles in the cubital tunnel seem not to be relevant to the occurrence of peripheral entrapment. Therefore, concerning the latter question, whether such nerves are more prone to compression is again debatable and remains to be clarified with future electrophysiological studies. Although magnetic resonance imaging is a sensitive diagnostic modality for evaluation of peripheral nerves, US is another alternative for peripheral nerve imaging, with its several advantages (convenience, costeffectiveness, repeatability, comparability, and lack of radiation exposure). Its ability to provide comparisons—as in our case—is also noteworthy. Overall, we call the attention of clinicians to the role of US in the management of CuTS. Further studies are warranted to provide insight into understanding the contribution (if any) of such anomalies in the causation of peripheral nerve entrapment syndromes.