Neurophysiological evaluation of patients with carpal tunnel syndrome using different diagnostic methods

Introduction

Carpal Tunnel Syndrome (CTS) is the most common form of median nerve entrapment.⁽¹⁾ It represents about 90% of all entrapment neuropathies.⁽²⁾ Diagnosis of CTS depends mainly on clinical evaluation and nerve conduction studies. Prolonged distal sensory and motor latencies, and reduced sensory and motor conduction velocities of median nerve around wrist have been accepted as diagnostic criteria for CTS.⁽³⁾ This study aims at studying sensitivities of different conventional and other modified neurophysiological methods in the diagnosis of carpal tunnel syndrome.

Patients and Methods

One hundred and nine hands of 83 patients with clinical presentation of CTS – whether unilateral or bilateral – have been included in this study in the period between August, 2022 and February, 2023. Patients have been recruited from the neurology outpatient clinic in Minia University Hospital. All patients were subjected to detailed history taking and meticulous neurological examination, and patients with clinical presentation that can be attributed to any other illness other than CTS were excluded. Hands were classified clinically as mild to moderate or severe according to the

modified criteria of the Italian CTS Study Group.⁽⁴⁾ Mild to moderate, include asympto-matic patients (Grade 0), patients with nocturnal paraesthesia (Grade I) and patients with nocturnal and diurnal paraesthesia (Grade II). Severe, include patients with sensory loss (Grade III) and patients with atrophy and/or weakness of median innervated thenar muscles (Grade IV).

Neurophysiological examination of all patients was done in the neurophysiology unit at Minia University Hospital. We used Neuropack MEB-2300 6 channel EMG/EP measuring system; Nihon Kohden Corporation, Tokyo, Japan.

Conventional methods used were:

Assessment of median nerve distal motor latency (DML) at wrist, values greater than 4.2 ms were considered diagnostic. All hands were examined by this technique.

Assessment of median nerve sensory conduction velocity (SCV) at index, values less than 44 m/s were considered diagnostic. Ninety one hands were examined by this technique.

Other modified methods used were:

Determining differences between median nerve motor latencies at palm and wrist, examined in 80 hands. Differences above 2.15 ms were considered diagnostic.

Determining differences between median and ulnar nerve distal motor latencies at wrist, examined in 68 hands. Differences above 1.4 ms were considered diagnostic.

Determining median nerve SCV at the middle finger, examined in 105 hands. Values less than 44 m/s were considered diagnostic.

Determining the differences between sensory latencies (SL) of median nerve at index and ulnar nerve at little finger, examined in 85 hands. Values above 0.4 ms were considered diagnostic.

Determining differences between SL of median nerve at middle finger and ulnar nerve at little finger, examined in 105 hands. Values above 0.4 ms were considered diagnostic.

Determining differences between SL of median and ulnar nerves at ring finger, examined in 74 hands. Values above 0.4 ms were considered diagnostic.

Determining median nerve SL at the palm by orthodromic technique, examined in 68 hands. Values above 1.85ms were considered diagnostic.

Determining the differences between SL of median nerve and ulnar nerve at palm by orthodromic techniques, examined in 42 cases. Values above 0.4ms were considered diagnostic.

Cut off values for conventional and modified techniques followed values reported by Kimura, (2013).^(5,6)

Statistical Analysis

The collected data were coded and statistically analyzed using IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp; 2011. Descriptive statistics were done for categorical data by number and percentage, while they were done for numerical data by mean, standard deviation and minimum and maximum of the range. Chi square test was used for qualitative data between groups if the number per cell was more than 5 and Fisher exact test if the number per cell was less than 5. The level of significance was taken at (P value ≤ 0.05).

Ethical Approval

Research has been conducted after approval of the Institutional Review Board of Faculty of Medicine, Minia University (Approval No. 651/2023). All patients signed an informed consent before the examination clarifying advantages and disadvantages of the study.

Results

One hundred and nine hands of 83 patients with clinical presentation of CTS have been included in this study in the period between August, 2022 and February, 2023. Age ranged between 16 and 65 years with a mean of 36.6 ± 21.34 years old. Female hands represented 93.5%. According to the modified criteria of the Italian CTS Study Group, 44 hands (40.36 %) were clinically classified as grade I, 29 hands (26.60%) were of grade II, 25 hands (22.93%) were of grade III and 11 hands (10.09%) were of grade IV.

The comparison between the sensitivities of assessment of the difference between median nerve motor latencies at palm and wrist and conventional methods (assessment of the median nerve DML and the SCV of median nerve at index) showed no significant difference.

Other results could be seen clearly in tables below (Tables 1, 2, 3, 4, 5, 6 and 7).

Discussion

The eight modified non-conventional techni-ques performed were chosen carefully to be easily applicable and of high probable sensitivity. It was difficult to apply all conventional and other modified techniques to all hands included in this study uniformly because it was painful and could not be afforded by most of patients, so there was variability in number of hands examined by each technique.

Regarding the two non-conventional motor techniques chosen in this study (differences between median nerve motor latencies at palm and wrist, and differences between median and ulnar nerve distal motor latencies at wrist), we thought they may add significant early diagnostic value, as it was reported that motor and sensory axons showed comparable incidences of abnormalities in patients with CTS. Ginanneschi et al., (2006) reported that CTS patients with selective involvement of sensory conduction in conventional studies show abnormalities of motor axon recruitment induced by submaximal stimulus intensities.⁽⁷⁾

Also, Rao and Maruthi, (2015) concluded that the motor conduction studies (including the median nerve motor latency at wrist and differences between median nerve motor latencies at palm and wrist) can be equally sensitive to sensory nerve conduction studies, and are no more difficult.⁽⁸⁾

Also we postulated that assessment of the median nerve sensory conduction velocity at middle finger may add more sensitive diagnostic value than that at index, as Uncini et al., (1989); and Terzis et al., (1998) concluded that recording from the thumb or middle finger or the lateral half of the ring finger often reveals abnormalities not detectable from the index finger.^(9,10) The relative sparing of the sensory branch to index might be explained by studying the anatomy of median nerve within the carpal tunnel. Compression of median nerve is usually most severe distally in the carpal tunnel, just proximal to its division into motor and sensory branches. At that level, nerve fibers giving rise to the branches to index lie most posteriorly with the least direct compressive and ischemic effects. ⁽¹¹⁾

According to our results, the most sensitive techniques used in our study were: 1) the differences between SL of median nerve at index and ulnar nerve at little finger 2) the differences between SL of median nerve at middle finger and ulnar nerve at little finger 3) the difference between SL of median and ulnar nerves at ring finger. That was in agreement with Astroshiand et al., (2003) who concluded that among the different motor and sensory nerve conduction tests they used, measurement of median-ulnar sensory latency difference had the highest diagnostic accuracy in patients with CTS.⁽¹²⁾

Technique 1 and 2 were significantly more sensitive than technique 3 especially in clinically mild to moderate patients. Differences were more obvious and showed higher significance with technique 2. But with the direct comparison between technique 1 and 2 differences were not statistically significant (Table 7). The superiority of technique 2 could be explained by the relative sparing of the index sensory branch in patients with CTS as discussed above, ^(9,10,11) and the relatively higher sensitivity of sensory conduction studies to digit three. Aydin et al., (2004) reported that the 1st digit showed the highest frequency of decreased conduction velocity. ⁽¹³⁾ Lauritzen et al., (1991); Padua and colleagues, (1997) reported that there were no significant differences in the sensitivities of median nerve SCV at the 1st and 3rd digits in their studies.^(14,15)