A prospective study examining the sensitivity of ultrasound determined median nerve cross-sectional area with nerve conduction investigation in the diagnosis of carpal tunnel syndrome

Abstract

Objectives

Carpal tunnel syndrome (CTS) is currently investigated with nerve conduction studies (NCS) for diagnosis, but these are expensive and invasive. We propose that ultrasound (US) will be comparable to NCS in diagnosing CTS.

Method

There were two groups in this study – a control (60 wrists) and symptomatic group (56 wrists), who all underwent a clinical examination. US measurements of the median nerve were the cross-sectional area of the carpal tunnel at the level of pisiform (CSAc), pronator quadratus (CSAp), 12 cm proximally in the mid-forearm (CSAmf) and palmar bowing of the flexor retinaculum. The main calculation was the CSA difference (CSAd = CSAc − CSAp).

Results

In the symptomatic group, NCS diagnosed 32/56 cases (sensitivity 57%). In the control group, the mean CSAc was 8.36 mm², CSAd of 0.57 mm², and palmar bowing 1.18 mm. The symptomatic group mean CSAc was 13.73 mm², CSAd of 5.02 mm², and palmar bowing 4.02 mm. With a threshold value of 10 mm² for the CSAc, 48/56 cases were diagnosed with CTS, with a sensitivity of 86% and specificity of 95%. For CSAd with a threshold at 2 mm, 50 cases were identified with CTS with a sensitivity of 89% and specificity of 97%. Palmar bowing had a sensitivity of 96% and specificity of 95%. NCS correlated strongly with CSAd (P = 0.007).

Discussion

In our study, the US results were statistically significant compared to NCS, with higher sensitivity and specificity. We propose that US should be the first line investigation for the diagnosis of CTS unless there are clinical indications to use NCS.

Keywords:

• Carpal tunnel syndrome
• Ultrasound
• Nerve conduction studies
• Median nerve