Usefulness of additional nerve conduction techniques in mild carpal tunnel syndrome

This study was done to assess the percentage of abnormality in additional nerve conduction techniques after normal median distal latency (routine) in mild carpal tunnel syndrome (CTS). Bilateral nerve conduction studies were carried out in 116 consecutive symptomatic CTS patients (153 hands). Mild cases were based on normal routine (< 3.7 ms, peak-measured, 14 cm) and at least one technique abnormal of the following: sensory median-radial difference (MR); sensory median-ulnar difference (MU4); mixed palm median-ulnar difference (MUP); median palm latency (PW); and motor median distal latency (MDL). After normal cut-off values for routine, 3.1 to 3.6 ms (< 3.7 ms), we found an abnormal MR, ranging from 86.6 to 93.4%, followed by MU4 (40 to 81.7%), MUP (20 to 71.2%), PW (0 to 41.1%), and MDL (0 to 19.6%). The most frequent abnormal association were MR plus MU4 in 90.1%, followed by MR plus MUP and MU4 plus MUP. The most frequent abnormal additional nerve conduction technique for mild CTS electrodiagnosis was MR, followed by MU4 and MUP. Percentage of MR abnormality was very high regardless of the median routine latency cut-off (< 3.1 to < 3.6 ms).