Ulnar Neuropathy due to Cubital Tunnel Syndrome Caused by Anconeus Epitrochlearis: A Case Report

Corresponding author: Byung-chul Son, MD, PhD Department of Neurosurgery, Seoul St. Mary’s Hospital, 222 Banpo-daero, Seocho-gu, Seoul, 06591, Republic of Korea Tel: +82-2-2258-6122 Fax: +82-2-594-4248 E-mail: sbc@catholic.ac.kr A 24-year-old, right-handed male patient presented with a 1-month history of continuous tingling paresthesia involving left medial hand and fingers accompanied by clumsiness of left hand and fingers. Thepain onset was sudden and marked by a severe aching pain in the medial elbow and medial scapular areas, without any prior cause. Two weeks of excruciating pain led to clumsiness of the left hand and fingers gradually occurred. Magnetic resonance imaging (MRI) of the left elbow revealed a swollen ulnar nerve with perineural enhancement involving anconeus epitrochlearis (AE) muscle within the cubital tunnel. The operation revealed adhesion of the AE muscle to the left ulnar nerve. Open in-situ decompression of the ulnar nerve without transposition eventually alleviated the pain and weakness associated with ulnar neuropathy. The patient slowly recovered 6 months after surgery. The AE muscle is a common anatomic variation, with a prevalence of up to 34%. However, the prevalence of ulnar neuropathy associated with the AE muscle is unknown. It is a congenital accessory muscle between the medial humeral epicondyle and the olecranon covering the posterior aspect of the cubital tunnel. It is usually diagnosed intraoperatively and not preoperatively in the absence of no imaging studies. The clinical presentation of ulnar neuropathy caused by the AE usually differs from idiopathic disease, including younger age at onset, rapid progression with a short duration of symptoms, and edema of the AE muscle on the MRI.