Carpal tunnel syndrome (CTS) is one of the most frequent compressive neuropathies of the upper extremities, accounting for 90% of all entrapment neuropathies2,12). In a recent surveillance study by Bland et al., the annual incidence was 139.4 cases per 100,000 in females and 67.2 cases per 100,000 in males, with a female to male ratio of 2.07173).

Carpal tunnel release (CTR), which consists of the division of the transverse carpal ligament to increase the space in the carpal tunnel, is indicated in patients with moderate to severe CTS. The success rate of CTR in patients with CTS has been reported to be 70 to 90%9,12). The outcome of CTR can be different between patients with isolated carpal tunnel syndrome and patients with coexisting cervical radiculopathy5). However, the correlation between co-existing double crush syndrome and the outcome of CTR still remains controversial.

The aim of this study is to elucidate the incidence of electrophysiologically proven cervical radiculopathy and its effect on the postoperative prognosis of CTR.

During the study period, 85 patients were treated by either open or endoscopic CTR for CTS. Of the study population, 79 were women and 6 were men. The mean age of the patients was 58.86±10.94 years (range, 31 to 86 years). The demographics of the patients are listed in Table 1. The preoperative clinical diagnosis of CTS was made in all 85 patients according to their history and the results from the combination of NCS, EMG and ultrasonographic evaluation of the carpal tunnel. Forty-six (54.1%) of the 85 patients had an MRI or X-ray of the cervical region. The patients were divided into the following three groups based on the findings of the radiographic assessments of the cervical region: neural foraminal stenosis (26 patients), central canal stenosis (2 patients) and spondylosis (10 patients). Of the 85 patients, 17 were proven to have cervical radiculopathy on NCS and EMG.

The difference in the outcome between endoscopic and open CTR was not considered to be different for long-term pain relief based on a previous study12).

The outcome of CTR was available for assessment in 84 of 85 patients. Among these patients, CTR was shown to be effective for 70 (83.3%) of 84 patients.

The effect of CTR was assessed based on the patient’s clinical characteristics (Table 2 and 3). The mean age of the patients was not significantly different between the effective and non-effective groups. There was no significant difference in the preoperative severity of CTS between the effective and non-effective groups (p=0.186). The presence of cervical radiculopathy, which was proven by neurophysiological assessments (NSC and EMG), was the only factor that was significantly different between the effective and non-effective groups (p= 0.05). The degree of pain relief that was graded from 1 to 4 based on each patient’s response was not significantly different among the groups with different findings on the radiological cervical evaluation (p=0.17). Abnormal findings in radiological assessment did not give the significant difference in outcome of CTR to both groups with and without cervical radiculopathy (p=0.571 and p=0.165, respectively). The outcome of CTR was not significantly different according to the presence of diabetes mellitus (p=0.13). The mean value of the preoperative severity of CTS in patients with diabetes mellitus was not significantly different from those without diabetes mellitus (p=0.81).

Upton and McComas first described double crush syndrome in 1973 based on their clinical observation that the majority of patients had median or ulnar neuropathy associated with evidence of cervicothoracic root lesions, suggesting that compression of an axon at one location makes it more sensitive to the effects of compression in another location because of impaired axoplasmic flow. They also observed a high association between diabetes and CTS13).

Based on the fact that median nerve sensory fibers primarily use C6 and C7 roots and that motor fibers primarily use C8 and T1, some authors have tried to corroborate the hypothesis that abnormal sensory conduction of the median nerve would be found more frequently in those patients with C6 or C7 radiculopathy4).

The results of previous studies have shown discrepancies in the relationship between cervical pathology that can cause double crush syndrome and CTS.

In the one of the largest studies by Hurst et al., there was a significant correlation of bilateral carpal tunnel syndrome with cervical arthritis (p<0.05), whereas a recent study by Kwon et al. showed that double crush syndrome in CTS did not explain the correlation between the level of cervical radiculopathy and median nerve motor or sensory responses. In their study, the frequency of coexisting CTS was not significantly different according to the level of radiculopathy10).

Of the neuropathic factors, it has been suggested that patients with diabetes mellitus have a higher tendency to develop CTS without necessarily increasing interstitial pressure within the carpal tunnel, due to a lower threshold for nerve damage7,11).

Hurst et al. also showed a tendency for an increased incidence of bilateral CTS in patients with co-existing diabetes mellitus, although this increase was not statistically significant6).

In our study, 13 (15.3%) of 85 patients had co-existing diabetes mellitus; however, neither the preoperative severity of CTS nor the postoperative outcome of CTR was significantly different from patients without diabetes mellitus (p= 0.81 and 0.13).

Although the presence of ipsilateral cervical radiculopathy at C6, C7 or C8 did not have a significant correlation with the preoperative severity of CTS in our study, it was significantly related to a poorer postoperative outcome for CTR. However, our study showed that there was no significant difference in the outcome of CTR according to each radiological diagnosis in the cervical region, including neural foraminal stenosis, central canal stenosis and cervical spondylosis.

Hence, the results from our study support the concept of double crush syndrome in CTS patients. Based on the results of our study, preoperative neurophysiologic studies such as NCS and EMG are necessary to identify the patients with cervical radiculopathy who may be less likely to benefit from CTR for their symptom relief. In contrast to the utility of preoperative electrophysiological assessments to identify cervical radiculopathy, radiological evaluation seems insufficient to predict a patient’s prognosis after surgical decompression of carpal tunnel.

Thus, taking cost-effectiveness into consideration, preoperative neurophysiologic evaluation to determine the severity of CTS and evidence of cervical radiculopathy would occur prior to cervical radiographic evaluation, and radiologic evaluation may be omitted if cervical radiculopathy is not proven by neurophysiologic assessments.

The limitation of our study is that the factors of confounding potential that are known to be associated with poor surgical prognosis1 such as patient occupation, repetitive work and atrophy of the abductor pollicis brevis muscle were not considered in the preoperative evaluation.

Therefore, further clinical study should be performed while controlling for possible confounding factors.