Which ultrasound method has the upper hand in the follow-up of the patients with recurrent carpal tunnel syndrome?
I read with great interest the study of different diagnostic
ultrasound measures of median nerve volume in patients with carpal tunnel
syndrome (CTS) by Dejaco et al. (1). It is of great value, in my opinion,
that this study succeeded not only in highlighting the diagnostic value
and good reliability of ultrasound determination of median nerve cross
sectional area (CSA) in patients with suspected CTS, but also confirmed
previously reported results on the value of Doppler ultrasonography in
classifying the severity of CTS (2-4).
I would like though to draw attention to a subgroup of patients, with persistent clinical and electrophysiological signs of CTS and condition after unsuccessful carpal tunnel release (CTR). The etiology of the persistent neurological semiology is in most of the cases an incomplete release of the retinaculum flexorum. Traction neuropathy, real recurrent CTS and iatrogenic nerve lesions occur less frequently. Nerve conduction studies are a valuable tool in supporting the indication for a reoperation, if a preoperative examination exists, but are not able to demonstrate the exact cause of a failed CTR. Several ultrasonography studies after CTR (5-8) have all concluded that the functional outcome and the CSA of the median nerve, may provide clinicians with a tool to estimate the response of these patients to surgery and the indication for reoperation. The difficulty though to quantify pathological changes after CTR remains an important limitation of neuromuscular ultrasound in clinical practice.
I would like therefore to report the preliminary data of the clinical, electrophysiological and ultrasound follow-up of 10 patients (mean age 53.46, SD +/- 14.8, 2 women) with CTS, who underwent due to persistent neurological semiology CTR two times. Functional Status Scale (9) was used for the clinical evaluation, while distal motor latency (DML) and CSA of the median nerve (carpal tunnel inlet) were used as electrophysiological and ultrasound markers for the follow-up. In addition, a retrospective analysis of the already acquired power-doppler ultrasound images of the median nerve at carpal tunnel inlet has been performed, in order to calculate for each patient the power-Doppler score according to the study protocol from Dejaco et al. (1). According to the preliminary data of this study the CSA and the power- Doppler score at the inlet of the carpal tunnel seem to highlight well the functional recovery of the patients after the second CTR (Table 1). On the other hand, the DML values of the median nerve showed no statistical significant changes pre- and postoperarive, failing to resemble the clinical improvement of the patients. A possible explanation could be, that the edema caused by the chronic nerve compression and the consecutive increased endoneurial pressure may have lead to nerve ischemia. This pathophysiologic cascade leading to secondary ischemic neuropathy may result in the observed reduced nerve excitability.
Therefore, systematic, multicentre, prospective studies are needed to evaluate the applicability and diagnostic values of these findings and to understand the complex sonology of CTS.
Preoperative: FSS mean 25.6 (SD 5.2), CSA: mean 13.12mm2 (SD 1.5), DML: mean 8.9ms (SD 3.5), PDS: mean 1.2 (SD 0.42)
CTR-1: FSS: mean 23.2 (SD 4.3, p=0.2755), CSA: mean 12.5mm2 (SD 2.3, p=0.4844) DML: mean 8.3ms (SD 2.1, p=0.6476) PDS: mean 0.7 (SD 0.48, p=0.086)
CTR-2: FSS: mean 20.1 (SD 4.3,p=0.019) CSA: mean 11.2mm2 (SD 1.9, p=0.021) DML: mean 7.9ms (SD 4.1,p=0.5647) PDS: mean 0.6 (SD 0.51, p=0.01)
FSS = functional status scale CSA = cross sectional area (mm2) DML=distal motor latency (ms) PDS: Power Doppler Score SD = standard deviation CTR-1: First carpal tunnel release operation CTR-2: Second carpal tunnel release operation
Tables and Legends Table 1 Title: Overview of the clinical, electrophysiologic and sonographic follow up of the median nerve in the study group.
Legend: Statistical comparison of groups were performed with the help of Student's t test or. P-values < 0.05 were considered as statistically significant.
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9. Levine DW, Simmons BP, Koris MJ et al. A self-administered questionnaire for the assessment of severity of symptoms and functional status in carpal tunnel syndrome J Bone Joint Surg Am. 1993 Nov;75(11):1585-92.
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