In this study, it was found that the average age of CTS patients was 54.43 ± 10.47 years, the male to female ratio was about 1/4.5, and the incidence of females was much higher than that of males. The results of this study are similar to those of previous studies(1, 9, 10). The higher incidence of women may be caused by a combination of factors such as women taking on more housework in the family and changes in the hormone levels in women. Among the types of patients, bilateral incidence is the most (82%), and the number of patients on the right side is more than that on the left side, which is consistent with previous studies(9, 11, 12). The greater incidence on the right side than on the left may be due to the fact that the majority of people are right-handed and have more repetitive movements than left.
Some studies have shown that patients with CTS may have ulnar nerve damage(13, 14). A study found that when patients with CTS underwent carpal tunnel release, the pressure in Guyon's canal is reduced and the sensory conduction of the ulnar nerve improves(13). However, in several studies with larger numbers of patients, ulnar nerve conduction was found to be unaffected in patients with CTS(15–17). In our study, 179 affected wrists were included, a high number included, and there were no significant differences when USDL was compared with controls and when USDL was compared between different severities of CTS, these suggest that the ulnar nerve was not significantly damaged in patients with CTS.
We found that the MSDL and MUD of 179 wrists were significantly different from the control group, P < 0.05, and the AUC of MUD was 1, the AUC of MSDL was 0.942, both of which have high diagnostic accuracy. MUD AUC > MSDL AUC, which indicates that MUD is more accurate than MSDL in diagnosing CTS, which is consistent with the results of many studies reported so far(2, 3, 18, 19). And this difference may be due to individual differences, such as age, gender, weight, work, etc., resulting in different individual neurological status, such as older patients, due to the increase in age, neurological function decline, MSDL and USDL measurement The values are relatively prolonged. The simple prolongation of MSDL does not indicate that CTS can be diagnosed, but comparing with its own UN and calculating MUD can explain the problem better. Most of the previously reported MSDL cut-off values were between 2.7–3.8 ms, and more were around 3.7 ms, the sensitivity is 67%~90%, and the specificity is mostly greater than 90%(3, 11, 12, 18, 20–23). In our study, the sensitivity of MSDL to diagnose CTS was 85.5%, and the specificity was 90.4%, which was similar to the results of previous studies.
However, our study found that the optimal cut-off value of MSDL was 2.465 ms, which was smaller than the previously reported results. It may be that 97.7% of the total number of mild and moderate patients in this study were far more than severe, resulting in a lower MSDL value. Our study shows that when diagnosing CTS, compared with the current belief that the MSDL critical value is located at 4ms, it is possible to diagnose CTS at a smaller MSDL. We found that the best cutoff value of MUD to diagnose CTS was 0.38ms, the sensitivity was 100%, and the specificity was 100% (Fig. 1). Past studies have found that the diagnostic cut-off value is about 0.35ms ~ 0.81ms, the sensitivity is 85%~90%, and the specificity is 85%~96.7%(3, 11, 18, 20, 24, 25). We found that the optimal cutoff value of MUD for diagnosing CTS is 0.38ms, which is consistent with the results of previous studies. The difference is that the sensitivity and specificity of this study are 100%, which are higher than previous studies. It may be due to that the control group was derived from the contralateral hand of the unilateral affected wrist, which has good comparability.
In the study, it was found that there were significant differences in MSDL between the control group and mild /moderate /severe, and between the mild and moderate CTS patients, and from the box plot (Fig. 3A), it can be found that the heavier the severity, the larger the MSDL, and from the correlation analysis, it is found that there is a positive correlation between MSDL and severity (rs = 0.745, rs > 0), indicating that the severity of CTS increases as the MSDL increases. In addition, there were significant difference in MUD between control group and mild/moderate/severe group, and between mild and moderate CTS patients, from the box plot (Fig. 3B), it is found that the heavier the severity, the larger the MUD, and from the correlation analysis, it is also found that there is a positive correlation, it is found that there is a positive correlation between MUD and severity. The correlation coefficient of MUD (rs = 0.755) is larger than that of MSDL (rs = 0.745), indicating that the correlation between MUD and NCS severity is better than that of MSDL, which is consistent with our previous finding that MUD AUC > MSDL AUC, MUD is more accurate than MSDL in diagnosing CTS.
In previous studies, as well as in this study, the CTS electrophysiological severity grading method published by Padua et al(26). The complete MN motor conduction and sensory conduction are needed to distinguish the severity. This study found that MUD is correlated with the severity of CTS. For patients who are more sensitive to pain and cannot tolerate electrical stimulation, perhaps only measuring MUD can reflect the severity and reduce the pain of the patient, which can further guide the patient to choose an appropriate treatment plan.