Characteristics of nerve conduction studies in carpal tunnel syndrome

Numerous nerve conduction tests are used for the electrodiagnosis of carpal tunnel syndrome (CTS), with a wide range of sensitivity and specificity reported for each test in clinical studies.

The purpose of this study was to compare the diagnostic accuracy of various nerve conduction tests and determine the properties of the most accurate test.

A prospective observational case control study.

Eighty patients with clinically confirmed CTS and 80 asymptomatic healthy controls were included in the study. All patients underwent the routine hematological investigations as per the protocol. All cases and controls were subjected to various nerve conduction study protocols for CTS. Results were analyzed statistically.

The two-tailed Student's t-test was used for the comparative statistical analysis. The sensitivity of each test was calculated as (the number of hands with an abnormal study result/the number of CTS hands) × 100. Comparison between percentages was performed by the McNemar test.

The mean age was 38.19 ± 10.13 years and the female:male ratio was 1.5:1. The mean duration of disease was 0.89 ± 0.61 years. Hypothyroidism was present in 21 (26.25%) patients, whereas 13 (16.25%) and 4 (5%) patients had diabetes mellitus and rheumatoid arthritis, respectively. The median nerve motor latency was 4.73 ± 0.83 ms while the sensory latency was 3.44 ± 0.56 ms. The median nerve orthodomic sensory latency was found to be 2.57 ± 0.31 ms. The conduction velocity across the palm and wrist was 41.37 ± 0.67 ms. The sensitivity was the highest in the inching method (86.25%) and lowest for the conventional median motor and sensory latencies (56.25% and 45%, respectively).

Addition of a single test of median and ulnar sensory latency, the median and radial sensory latency or the inching method, in routine protocol will improve the sensitivity for the diagnosis of CTS in all patients.