Evaluating botulinum toxin as a novel therapeutic for cubital tunnel syndrome induced by anconeus epitrochlearis muscle

초록

Background and aims: Cubital tunnel syndrome (CuTS) is the second most common entrapment neuropathy. Among its less frequent causes is hypertrophy of the anconeus epitrochlearis (AE) muscle, which can compress the ulnar nerve within the cubital tunnel. Though conservative management and surgical decompression are standard treatments, surgery can be invasive and complex. Drawing from the use of botulinum toxin in other muscular compression syndromes, this study evaluates its efficacy as a minimally invasive treatment for AE-related CuTS. Methods: A retrospective review was conducted on nine patients (11 limbs) diagnosed with AE-related CuTS between 2015 and 2022. Clinical signs, electrophysiologic studies, and ultrasonographic measurements of the AE and ulnar nerve were assessed before and after botulinum toxin injection. Results: Post-treatment, motor symptoms improved in 5/6 cases, sensory symptoms in 5/11. Tinel’s sign positivity decreased from 8 to 1 case, and the elbow flexion test from 10 to 1. Median subjective improvement was 80 %. Ultrasonography revealed a significant reduction in AE and ulnar nerve cross-sectional areas. AE muscle size showed significant negative correlations with motor conduction velocity, ADM amplitude ratio, and ulnar sensory amplitude. Fisher’s exact test confirmed significant clinical improvement (except for motor symptoms), and Wilcoxon tests showed significant morphological change. Conclusions: Botulinum toxin injection into the AE muscle represents a safe, minimally invasive, and effective treatment for CuTS caused by AE hypertrophy. It leads to meaningful clinical improvement and reduction in compressive muscle mass, providing a promising non-surgical option for patients with this rare but significant cause of ulnar nerve entrapment.