A study of interpolation method in diagnosis of carpal tunnel syndrome

Context:

The low correlation between the patients’ signs and symptoms of carpal tunnel syndrome (CTS) and results of electrodiagnostic tests makes the diagnosis challenging in mild cases. Interpolation is a mathematical method for finding median nerve conduction velocity (NCV) exactly at carpal tunnel site. Therefore, it may be helpful in diagnosis of CTS in patients with equivocal test results.

Aim:

The aim of this study is to evaluate interpolation method as a CTS diagnostic test.

Settings and Design:

Patients with two or more clinical symptoms and signs of CTS in a median nerve territory with 3.5 ms ≤ distal median sensory latency <4.6 ms from those who came to our electrodiagnostic clinics and also, age matched healthy control subjects were recruited in the study.

Materials and Methods:

Median compound motor action potential and median sensory nerve action potential latencies were measured by a MEDLEC SYNERGY VIASIS electromyography and conduction velocities were calculated by both routine method and interpolation technique.

Statistical Analysis Used:

Chi-square and Student''s t-test were used for comparing group differences. Cut-off points were calculated using receiver operating characteristic curve.

Results:

A sensitivity of 88%, specificity of 67%, positive predictive value (PPV) and negative predictive value (NPV) of 70.8% and 84.7% were obtained for median motor NCV and a sensitivity of 98.3%, specificity of 91.7%, PPV and NPV of 91.9% and 98.2% were obtained for median sensory NCV with interpolation technique.

Conclusions:

Median motor interpolation method is a good technique, but it has less sensitivity and specificity than median sensory interpolation method.Key Words: Carpal tunnel syndrome, electrodiagnosis, interpolation, nerve conduction velocity