Effect of carpal tunnel syndrome on median nerve proximal conduction estimated by F-waves

Electrodiagnostic approach in entrapment neuropathies of the median and ulnar nerves

OBJECTIVE

The present study's aim was to analyze the late responses' parameters in order to determine the utility of each one.

METHODS

The study, conducted on a total of 325 patients with entrapment neuropathy of the median nerve and 36 with entrapment neuropathy of the ulnar nerve, included the bilateral evaluation of the median and the ulnar nerve and analysis of 20 F-wave and 4 A-wave parameters.

RESULTS

The authors emphasize the necessity of bilateral examination and that of examining the ipsilateral ulnar/median nerve, such as to calculate the difference in F-wave average latency of the median/ulnar and the ipsilateral ulnar/median nerve. This was the most sensitive parameter studied, altered in more than 70% of cases, significantly in more cases than when using only the M-wave distal latency. Also there was a statistically significant correlation between patient age and F-wave latency.

CONCLUSIONS

The completed research yielded the recommendation for F-wave parameter studies to include the difference in F-wave average latency of the median/ulnar and the ipsilateral ulnar/median nerve. This parameter was also included in the composite score, along with the recommendations of the American Academy of Emergency Medicine (AAEM).

Low sensitivity of F-wave in the electrodiagnosis of carpal tunnel syndrome

OBJECTIVE

Previous studies showed "F-wave inversion" (F-INV) as a sensitive method in the electrodiagnosis of early stage of carpal tunnel syndrome (CTS). This study aimed at evaluating the sensitivity and specificity of F-wave and nerve conduction velocity (NCV) testing in CTS.

METHODS

We consecutively enrolled 244 cases and 108 controls. F-waves analysis included: Fwave minimum and mean latencies, F-wave persistence and chronodispersion, mean-F/CMAP amplitude ratio, F-INV. Specificity and sensitivity of F-waves parameters were calculated in the whole sample of CTS patients and by grouping the patients according to CTS severity. Multivariate logistic regression was also performed using F-INV as a dependent variable.

RESULTS

In the whole sample the sensitivity of F-mean-INV and of median-ulnar NCV comparative testing was 50.8% and 93.7%, respectively. F-INV sensitivity dropped to 8% in CTS early stage. F-INV could be predicted only by distal motor latency of the median nerve. The sensitivity of all F-wave parameters increased only in the most severe stages of CTS.

CONCLUSIONS

This study does not confirm the electrodiagnostic usefulness of F-INV in early stage of CTS. All F-wave parameters, including F-INV, are much less sensitive than conventional NCV in CTS electrodiagnosis. F-wave does not add further useful information specifically related to CTS.

Neurophysiological study to assess the severity of each site through the motor neuron fiber in entrapment neuropathy

Background

The double crush hypothesis (DCH) that had been widely accepted seems to have been dismissed recently. Prior to the DCH, retrograde changes in the proximal median nerve in carpal tunnel syndrome (CTS) were reported. There has been no report of quantitative analyzing about the effect of one site's compression on another site all through the same peripheral nerve in CTS patients.

Methods

We measured the central motor conduction time (CMCT), motor conduction latency of the cervical root region (CRL), peripheral path latency from the rootlet to the wrist (PL) and motor distal latency (MDL) in the median nerve and ulnar nerves, respectively in CTS patients.

Results

MDL, PL and CRL were prolonged selectively in the median nerve, but not in the ulnar nerve of CTS patients. And in the median nerve measurement, MDL was high (r = 0.59, p < 0.0001) while PL showed a significant (r = -0.28, p < 0.05) relationship with CRL. MDL was large (r = 0.58, p < 0.0001) and showed a close (r = 0.59, p < 0.0001) relationship with the amplitude of CMAP. There was no significant difference between the amplitude of the normal CRL group and that of the prolonged CRL group. This quantitative analysis showed a linear relationship among MDL, CRL and CMAP amplitude.

Conclusion

Dual entrapment lesions did not unexpectedly exaggerate the vulnerability or total damage. The vulnerability and the damage were proportional to the severity of each lesion. If the DCH term presented to an unexpectedly exaggerated degree, the cases of double crush symdrome in the CTS patients were rare, but if the term DCH refers to only this linear relationship, the DCH should not be dismissed.

Reference values of F wave parameters in healthy subjects

OBJECTIVE AND METHODS

A large reference value database for F wave parameters was constructed with data from 121 to 196 healthy subjects; the age range of the subjects was 14-95 years. We studied the following parameters: minimum F wave latency (FMINLAT), mean F wave latency (FMEANLAT), maximum F wave latency (FMAXLAT), number of F waves/20 stimuli (FNUMBER) and F wave dispersion (FDISP=FMAXLAT-FMINLAT). The median, ulnar, peroneal and tibial nerves were studied.

RESULTS

Height explains almost half of the FMINLAT variability. The F wave latency increases with height in the arms by 0.2 ms/cm and in legs 0.4 ms/cm. The effect of age on F wave latency in the arms is relatively small, only 0.03 ms/year; and in the legs age increases the FMINLAT by 0.1 ms/year. Gender does not affect FMINLAT in a systematic way. The peroneal nerve has slightly longer FMINLAT than the tibial nerve, while the FNUMBER is higher in the tibial nerve than the peroneal nerve. The differences between the ulnar and median nerve are slight. There is a very high correlation between all 3 latency parameters (FMINLAT, FMAXLAT and FMEANLAT), but no correlation between FDISP and FNUMBER and the other parameters. Side to side comparisons reveals no significant differences in any of the parameters except for the median nerve FMINLAT and FMEANLAT, which is 0.2 ms longer on the right than left. If side difference of more than 2 standard deviation is taken as the upper limit for normal, the side difference in arms is 1.4 ms and in legs 3 ms. In repeated studies the interexaminer variability is small; the correlation coefficient between the different F parameters is high (P>0.6 in arms and P>0.7 in legs). In the arms the upper limit for a significant difference of FMINLAT on repeated studies in the median nerve is 1.0 and 1.7 ms for the ulnar nerve. In the legs, FMINLAT for the peroneal nerve is 2.6 ms and for the tibial nerve is 2.1 ms.

CONCLUSIONS

This large reference value database can be used not only to evaluate single measurements in relation with height and age, but also to compare right and left side and changes over time at repeated studies.

Carpal tunnel syndrome and hand configuration

The likelihood that hand configuration is related to the development of carpal tunnel syndrome (CTS) was examined in this study. Based on neurophysiological criteria, 50 female subjects with CTS and 50 healthy female controls were selected and their external hand dimensions were measured. Our results showed that the palm length and third digit length were significantly shorter and the palm width larger in the subjects with CTS compared with controls. Regression analysis demonstrated that the hand ratio [(palm + third digit length)/palm width] was significantly correlated with median nerve conduction measurements. The hand ratio may be a simple and useful predictive measurement in determining the tendency for CTS.

Surgical treatment of common entrapment neuropathies in the upper limbs

Entrapment neuropathies of the upper extremity are common, debilitating conditions. Most patients with these neuropathies are readily diagnosed on purely clinical grounds and may be effectively managed with nonoperative measures. However, the broad differential diagnosis often necessitates electrodiagnostic testing and radiographic imaging to clarify the situation. This review focuses on three of the most common entrapment neuropathies in the upper limbs: carpal tunnel syndrome (median nerve entrapment at the wrist), cubital tunnel syndrome (ulnar nerve entrapment at the elbow), and radial tunnel syndrome (posterior interosseous nerve entrapment). Anatomical considerations, patient evaluation, indications for surgical intervention, options for surgical approaches, outcomes, and complications are discussed.