Electrodiagnosis of ulnar nerve entrapment at the elbow

To evaluate the different localizing electrodiagnostic techniques of ulnar nerve entrapment at the elbow (UNE), particularly, comparison of the sensitivities of long segment stimulation across the elbow, versus short segment stimulation.

Patients who were referred to the Neurophysiology Laboratory of Haydarpasa Numune Training and Research Hospital, Istanbul, Turkey between 2000-2004 with a preliminary diagnosis of UNE were retrospectively evaluated. We compared the sensitivity of studying long segments (8-12 cm) versus short segments (3 cm) for the diagnosis of UNE in 93 limbs.

The study group consisted of 55 females and 31 males. Slowing of the conduction velocity (<50 m/sn) across the elbow was recorded in 48.4% of the limbs with long segment studies, and 73% of the limbs with short segment studies. In 82% of cases, an amplitude drop of the compound muscle action potential (CMAP) was also recorded. A CMAP amplitude drop of 10-30% between the wrist and elbow was recorded in 35 limbs (37.6%), while a drop of more than 50% was only recorded in 5 limbs (5.4%).

Short segment studies are sensitive for the electrodiagnosis of UNE, and although a CMAP amplitude drop is recorded in most patients, an amplitude drop consistent with a conduction block (>50%) is rare.