Abstract
In an interesting article, Ghasemi-Esfe et al. suggest that combined high resolution ultrasound (HRU) and color Doppler may be useful in diagnosing carpal tunnel syndrome (CTS) (1). The emerging importance of this diagnostic area is evident solely from observing the rapidly increasing numbers of publications in this area. We agree with the authors that HRU can already be used as a first-line diagnostic test to reduce both cost examination time and discomfort in patients with suspected CTS without loss of specificity and sensitivity as compared to electrodiagnostic tests (EDT). Based on the already established finding of median nerve hypervascularity playing an important pathophysiological role in CTS, the use of color Doppler ultrasound for diagnosing CTS is a new parameter worthwhile developing further.
The authors suggest that hypervascularity in combination with cross-sectional area of the median nerve, can predict CTS with sensitivity and specificity not different from EDT. However, even without the addition of color Doppler, sensitivity and specificity of HRU is similar to that of EDT (2). There are several important issues regarding color Doppler, which need addressing and concern how best to measure abnormal blood flow in the median nerve. Since the median nerve is richly supplied via nutrient vessels, it would seem that whether or not blood supply of a nerve can be shown, is mainly dependent on the technical characteristics of the ultrasound employed. The authors used a 9–13 MHz linear array probe (SONOLINE Antares; Siemens Medical Solutions, Erlangen, Germany) whereas a higher frequency, e.g. 18 MHz, with faster sampling rates and higher density array would be able to pick up blood flow in controls. Development of color Doppler will centre on development of indices that distinguish normal from abnormal nerve blood flow. The median nerve vascularization has been studied in detail in particular by Blunt (3). Abundant epineural, inter- and intra-fascicular vascular plexuses communicate via sympathetically regulated anastomosis. Since blood flow under sympathetic control experiences vasomotion (4), standardization of color Doppler flow will need to address the duration of testing as well as pay careful attention to temperature to compensate for temperature induced alterations in blood flow. From this, it is evident that the author's definition of hypervascularization of the median nerve as ‘any intraneural vascularity showing pulsatile blood flow’ is insufficient and that better definitions need to be established. Overall we agree that HRU together with color Doppler is developing into a simple, rapid, and readily accessible modality as an alternative to EDT of CTS. Careful standardization of color Doppler flow detection of the median nerve will further contribute to this.