Accessory Abductor Digiti Minimi: A Rare Cause or just an Incidental Finding in Carpal Tunnel Syndrome?

Resumen

The accessory abductor digiti minimi (aADM) is the most common accessory hypothenar muscle. Although most frequently asymptomatic, it can be a rare cause of compressive neuropathy due to mass effect over the ulnar nerve, but usually not over the median nerve. However, it may constitute a risk factor for median nerve compression if a close relationship between them is present. We describe two female patients, aged 54 and 60 years, that presented with unilateral carpal tunnel syndrome (CTS). Ultrasound studies (and an MRI in the youngest) showed proximal thickening of the median nerve with distal flattening, and an aADM muscle belly in close relationship with it. Compression of the median nerve by the aADM was surgically confirmed in the youngest patient. To our knowledge, there are no previously described cases of CTS caused by an aADM, only as an incidental finding and possible obstacle during carpal tunnel release.