The accessory abductor digiti minimi muscle (AADM) is a common anatomical variation that typically does not affect the ulnar nerve. However, a hypertrophic AADM can compress the ulnar nerve at the wrist by occupying space in Guyon's canal, particularly during repetitive movements or sustained pressure. Ulnar nerve compression is more frequent at the elbow than at the wrist. Neuromuscular ultrasound is increasingly used to visualize the ulnar nerve, identify variations like the AADM, and assess compression sites. This dynamic imaging technique helps confirm the diagnosis by visualizing both the nerve and accessory muscle within Guyon's canal.

We present two cases where neuromuscular ultrasound detected prominent AADM. The first case involved a 27 year-old man with progressive right-hand grip weakness and numbness in digits 4 and 5. The second case involved a 54 year-old man with progressive right hand numbness, specifically in digits 4 and 5, triggered by activities like sleeping, weightlifting, and driving. In both cases, ultrasound revealed ulnar nerve compression at the wrist, just proximal to Guyon’s canal, caused by a hypertrophic AADM, with significant flattening of the ulnar nerve at the level of the pisiform bone.

These cases highlight an unusual cause of ulnar nerve compression at the wrist due to hypertrophic AADM. Although the site of compression is less common, neuromuscular ultrasound provides an effective and affordable means of assessment. Detecting the accessory muscle can lead to significant positive outcomes following nerve decompression. Neuromuscular ultrasound should be considered when ulnar neuropathy is non-localizable, has a rapid onset of severe symptoms, is suspected despite normal electrodiagnostic studies, or when symptoms persist after decompression.