The anterior interosseous nerve latency in the diagnosis of severe carpal tunnel syndrome with unobtainable median nerve distal conduction.

This study assesses the role of the anterior interosseous nerve latency (AINL) in the differential diagnosis of severe carpal tunnel syndrome (CTS) with unobtainable median nerve distal conduction (UMNDC). The nonrandomized control trial took place at a referral center. Patients and other participants were categorized as follows: 25 healthy subjects; 25 patients with CTS; 11 patients with polyneuropathy; 5 men with mononeuritis and UMNDC; 2 men with pronator teres syndrome (PTS); 5 men with acute CTS and UMNDC; and 11 women with neglected CTS and UMNDC. The AINL was determined in all participants using surface and needle recordings. Electromyographic examination of the pronator quadratus (in all patients) and the median nerve innervated forearm muscles (in the last three groups of patients) was performed. Furthermore, surgical exploration of the median nerve at the wrist was performed in the 16 patients with CTS and UMNDC. The AINL obtained from patients was compared with the AINL of the control subjects. Also, the electrophysiological and surgical findings were compared. The AINL of control subjects ranged from 2.6 to 4.4ms (mean = 3.15 +/- 0.5) and from 3.1 to 5.2ms (mean = 3.95 +/- 0.5) on surface and needle recordings, respectively. The AINL in patients with CTS did not exceed the longest latency obtained from control subjects. The AINL was prolonged in patients with polyneuropathy and PTS, and unobtainable in patients with mononeuritis. Surgical exploration in the 16 patients confirmed the presence of severe median nerve compression at the wrist. Surface recording of the AINL could differentiate severe CTS with UMNDC, or with slow median motor nerve conduction velocity at the forearm, from median neuropathy or proximal compression.