[Comparison of mixed latency of ulnar and median nerve between wrist and elbow as diagnostic test of ulnar neuropathy in elbow].

INTRODUCTION: Conventional electrodiagnosis of ulnar neuropathy at the elbow is based on abnormalities in motor conduction across the elbow. However, sensory symptoms are predominant, and an accurate determination of the length of the nerve in this segment is difficult to obtain.

OBJECTIVE: We present an electrodiagnostic technique which helps to avoid these difficulties.

MATERIAL AND METHODS: We compared the mixed latency of ulnar and median nerve between wrist and above the elbow in 172 symptomatic and 407 asymptomatic ulnar nerves.

RESULTS: We determined that a difference of the mixed latency of ulnar and median nerve between wrist and above the elbow equal or higher than 1 ms had a sensitivity of 87% to an specificity of 91% for the diagnosis of ulnar neuropathy at the elbow. Moreover, a difference between both arms equal to or higher than 0.3 ms had a sensitivity of 80% and specificity of 91 %. If both conditions are present, the test is very specific (98%).

CONCLUSIONS: The measurement of the difference in mixed latency between ulnar and median nerves from wrist to above the elbow is a valuable tool for evaluating patients with suspected ulnar neuropathy at the elbow without motor involvement.