Musculoskeletal
Bergen e. Lemack, BS
Medical Student
Texas College of Osteopathic Medicine
Fort Worth, Texas, United States
Eliyah Malik, MS
Medical Student
Florida State University - College of Medicine
Newberry, Florida, United States
Omar Selod, DO
Physician
PMR Fort Worth
Fort Worth, Texas, United States
Bergen e. Lemack, BS
Texas College of Osteopathic Medicine
Fort Worth, Texas, United States
Asynchronous bilateral cubital tunnel syndrome (CuTS) due to an anconeus epitrochlearis (AE) muscle, with imaging-confirmed AE compressing the ulnar nerve despite a negative EMG.
Case Description:
A 51-year-old female with prior left-sided CuTS treated surgically in 2024 presented on 08/18/2025 with complaints of a 3-month history of right-sided hand numbness and paresthesias. She now describes a shooting pain that starts in her right elbow and radiates into the second and third digits, accompanied by an electric sensation. Physical exam revealed a positive Tinel’s sign at the right elbow. Hoffman’s was negative bilaterally. An EMG of the right upper extremity performed on 7/30/2025 was negative, but MRI of the right elbow revealed an interstitial tear of the proximal common extensor tendon with moderate tendinosis, as well as an accessory anconeus muscle within the cubital tunnel exerting chronic mass effect upon a mildly enlarged ulnar nerve.
Discussions:
The anconeus epitrochlearis (AE) is an accessory muscle present in up to 26.5% of individuals, though it is often asymptomatic. When hypertrophied, it can compress the ulnar nerve and lead to cubital tunnel syndrome (CuTS), which typically presents at a younger age with rapid progression. However, AE rarely causes CuTS; its prevalence is lower in patients with CuTS (4.5%) than in healthy individuals (14.2%), suggesting it is an uncommon contributor to ulnar neuropathy. We describe a rare case of bilateral AE-related CuTS with asynchronous progression, a pattern not previously reported in the literature. This case illustrates that AE can cause CuTS bilaterally with asynchronous progression. EMG may fail to identify AE-related ulnar nerve compression, emphasizing the importance of imaging for further evaluation.
Conclusions:
Clinicians should consider the possibility of AE as part of the differential diagnosis in patients with atypical or recurrent CuTs, even in the absence of EMG findings.
