Keywords
electroneuromyography - compressive neuropathy - carpal tunnel syndrome - ultrasonography
Introduction
Carpal tunnel syndrome (CTS) is the most common peripheral neuropathy due to compression
of the median nerve in the carpal tunnel.[1] Diagnosis is usually made through clinical history and physical examination,[2] while electroneuromyography (ENMG) assists in the diagnostic confirmation of dubious
cases and in the establishment of severity.[3]
Ultrasonography (US) was introduced as a diagnostic tool for CTS in the early 1990s[4] and was also used to diagnose some musculoskeletal disorders, such as ulnar nerve
and fibular nerve neuropathy.[5]
[6]
[7] One of the typical findings related to CTS is the increase in the cross-sectional
area of the median nerve proximal or distal to the compression site.[8] Other findings that can be identified by this examination are decreased echogenicity
and nerve mobility, increased vascularization and anatomical variations of the median
nerve, which may contribute to the compressive clinical picture. Electroneuromyography,
in turn, is considered the diagnostic method of choice for people suspected of having
peripheral neuropathies, providing additional information on myelin dysfunction and
axonal loss.[9]
Studies directly comparing the classification of ENMG and US positivity for the diagnosis
of CTS are scarce. Moreover, we observed in our clinical practice a large number of
people with clinical picture compatible with CTS and results of divergent tests. Our
study aims to verify whether there is an association between the results of the ENMG
and the positivity of US in the diagnosis of CTS.
Casuistry and Methods
An observational, cross-sectional, quali-quantitative study was conducted with evaluation
of 68 patients scheduled consecutively in a 4-month period in a regional reference
hand surgery outpatient clinic. All procedures were performed according to ethical
standards determined by the Research Ethics Committee for research in human beings,
and by the Helsinki Declaration of 1964. The free and informed consent form was obtained
from all participants by signing a specific term.
The inclusion criteria were people of both genders, over 18 years of age, who presented,
at the initial consultation, ENMG of upper limbs and US of wrist, both with diagnostic
hypothesis of CTS. We excluded people with other neuropathies, previous wrist injuries,
pregnant women, people with reports of tenosynovitis or tumors in the wrist, those
with a known history of uncontrolled systemic comorbidities, and people with reports
of current work activities with repetitive movements or hand vibration.
In relation to US, in our service, the medical team specialized in radiology and imaging
diagnosis defines the sectional cutoff point of the median nerve suggestive of abnormality
at 10 mm or more. The ENMG, in turn, is performed by the same neurologist specialized
in electroneuromyographic studies, belonging to the clinical staff of the institution.
The classification of ENMG is thus standardized: mild degree (alteration only of sensory
conduction), moderate degree (alteration of sensory and motor conduction) and severe
degree (altered sensory and motor conduction and signs of denervation to needle electromyography).
The qualitative characteristics were evaluated in all patients and described using
absolute and relative frequencies. The quantitative variable age was described using
summary measures (mean, standard deviation, median, minimum and maximum).
Seventy-six people were attended and 8 were excluded (1 with previous wrist trauma,
2 with uncontrolled diabetes, and 5 with previous wrist surgeries), totaling 68 participants
included in this study.
[Table 1] shows the clinical characteristics of the 68 people who constituted our sample.
Regarding gender, there were 61 women (89.7%) and 7 men (10.3%). The mean and standard
deviation of age was 54.4 years ± 10.1. Regarding the employment situation, 24 people
(35.3%) reported being retired or housewives, while 44 (64.7%) were in current work
activity. Sixty-five people (95.6%) reported being right-handed and 3 (4.4%) left-handed.
Regarding the side affected by symptoms,14 people reported symptoms only on the right
(20.6%), 6 (8.8%) only on the left, and 48 (70.6%) reported bilateral symptomatology.
When asked about comorbidities, 28 people (41.2%) denied having any comorbidities,
while 24 (35.3%) reported having a systemic disease, and 16 (23.5%) 2 or more.
Table 1
|
Variable
|
Description (N = 68)
|
|
Age (years)
|
|
|
mean ± SD
|
54.4 ± 10.1
|
|
median (min.; max.)
|
53.5 (35; 76)
|
|
Gender, n (%)
|
|
|
Female
|
61 (89.7)
|
|
Male
|
7 (10.3)
|
|
Profession, n (%)
|
|
|
Housewife/retired
|
24 (35.3)
|
|
In work
|
44 (64.7)
|
|
Dominance, n (%)
|
|
|
Right
|
65 (95.6)
|
|
Lefty
|
3 (4.4)
|
|
Affected side, n (%)
|
|
|
Right
|
14 (20.6)
|
|
Left
|
6 (8.8)
|
|
Both
|
48 (70.6)
|
|
Comorbidities, n (%)
|
|
|
One systemic disease
|
24 (35.3)
|
|
Two or more systemic diseases
|
16 (23.5)
|
|
No reported disease
|
28 (41.2)
|
The US results (positive or negative) were crossed with the results of the ENMG (mild,
moderate, or severe) and the existence of association with the use of the Chi-squared
test was verified. [10] Kappa [11] coefficients of agreement were calculated to verify the degree of agreement between
US and ENMG, as well as diagnostic measures sensitivity, specificity, positive predictive
value (PPV), and negative predictive value (NPV), to evaluate the prediction of CTS
using US.
The SPSS for Windows version 20.0 software (IBM Corp., Armonk, NY, USA) was used to
perform the analyses, and Microsoft Excel 2003 software (Microsoft Corp., Redmond,
WA, USA) was used to tabulate the data. The tests were performed with a significance
level of 5%.
Results
Using the hand as a sampling unit, [Table 2] shows the crossing between US and ENMG, and the result of statistical tests and
diagnostic measures. From the 136 hands evaluated, 123 presented positive ENMG for
CTS and 13 presented a negative result. Regarding the classification of the ENMG,
there were 19 mild (15.5%), 33 (26.8%) moderate, and 71 (57.7%) severe cases. From
the 19 hands with mild degree ENMG, 12 (63.2%) had negative US for CTS and 7 (36.8%)
had a positive result. In relation to the 33 hands with moderate degree ENMG, 19 (57.6%)
had negative US for CTS and 14 (42.4%) positive. From the 71 hands with severe degree
ENMG, 25 (35.2%) had negative US for CTS and 46 (64.8%) positive. Finally, from the
13 hands with negative ENMG (normal ENMG), 8 (61.5%) had negative US for CTS and 5
(38.5%) positive.
Table 2
|
Variable
|
US for CTS
|
Total
|
p
|
Kappa
|
Sensitivity
|
Specificity
|
PPV
|
NPV
|
|
Negative (N = 64)
|
Positive (N = 72)
|
N = 136
|
95% CI
|
95% CI
|
95% CI
|
95% CI
|
95% CI
|
|
ENMG
|
|
|
|
0.036
|
|
|
|
|
|
|
Normal
|
8 (61.5)
|
5 (38.5)
|
13
|
|
|
|
|
|
|
|
Mild
|
12 (63.2)
|
7 (36.8)
|
19
|
|
|
|
|
|
|
|
Moderate
|
19 (57.6)
|
14 (42.4)
|
33
|
|
|
|
|
|
|
|
Serious
|
25 (35.2)
|
46 (64.8)
|
71
|
|
|
|
|
|
|
|
ENMG
|
|
|
|
0.271
|
0.058
|
54.5
|
61.5
|
93.1
|
12.5
|
|
Normal
|
8 (61.5)
|
5 (38.5)
|
13
|
|
(-0.046; 0.162)
|
(45.2; 63.5)
|
(31.6; 86.1)
|
(84.5; 97.7)
|
(5.6; 23.2)
|
|
Altered
|
56 (45.5)
|
67 (54.5)
|
123
|
|
|
|
|
|
|
|
ENMG
|
|
|
|
0.045
|
0.150
|
57.7
|
62.5
|
83.3
|
31.3
|
|
Normal/mild
|
20 (62.5)
|
12 (37.5)
|
32
|
|
(0.003; 0.297)
|
(47.6; 67.3)
|
(43.7; 78.9)
|
(72.7; 91.1)
|
(20.2; 44.1)
|
|
Moderate/severe
|
44 (42.3)
|
60 (57.7)
|
104
|
|
|
|
|
|
|
|
ENMG
|
|
|
|
0.004
|
0.248
|
64.8
|
60.0
|
63.9
|
60.9
|
|
Normal/mild/moderate
|
39 (60)
|
26 (40)
|
65
|
|
(0.085; 0.411)
|
(52.5; 75.8)
|
(47.1; 72.0)
|
(51.7; 74.9)
|
(47.9; 72.9)
|
|
Serious
|
25 (35.2)
|
46 (64.8)
|
71
|
|
|
|
|
|
|
Discussion
In population-based studies, the prevalence of CTS is higher in women and increases
with aging,[10] with an estimated involvement up to three times more than men.[11] This can be explained by the fact that women have a lower size cuff [12] and lower carpal tunnel elasticity, which can contribute to lower compliance and
accommodation of structures.[13]
[14] It is possible that women are predisposed to more rectified tunnels, which may also
contribute to the development of CTS.[15] Based on these publications, our work is in agreement with the literature, with
a high prevalence of CTS involvement in women.
In the United States, CTS is the third cause of work leave.[16] In our study, 35.3% of people with CTS reported being retired or housewives, while
the majority reported being in current work activity.
Some risk factors for CTS include personal and family history, diabetes, obesity,
hypothyroidism, pregnancy, and rheumatoid arthritis.[17] In our series, more than half of the people had at least one systemic comorbidity,
and the most common among them were hypertension, diabetes and hypothyroidism.
The definition of the sectional cutoff point of the median nerve by US, suggestive
of CTS, is controversial. Most articles set the value between 8 and 14 mm.[18] In our institution, the medical team stipulates the value equal to or greater than
10 mm as suggestive of abnormality. According to Özçakar et al.,[19] US has the advantage of being low-cost, user-friendly, noninvasive, portable, available
in most health services and well tolerated by patients, an opinion also shared by
Horng et al.[20] however, these authors indicate the examination as a complement to the ENMG. In
contrast, Mhoon et al.[21] do not find a significant correlation between ultrasound parameters and electrophysiological
severity, and conclude that US is not able to determine the severity of CTS. For Abrishamchi
et al.,[22] US may be complementary, but not conclusive, in relation to the classification of
CTS severity. According to Fowler et al.,[8] US and ENMG have diagnostic accuracy similar to clinical tests, but ENMG can diagnose
other etiologies of paresthesia in the hands besides CTS, such as cervical radiculopathy,
cubital tunnel syndrome and prone syndrome.[23]
[24]
Our study demonstrated that there was a statistically significant association between
ENMG and US (p < 0.05), and US positivity was higher for more severe levels of CTS given by ENMG.
Certainly, this fact is related to the sensitivity and scope of the US method. Median
nerve changes secondary to more advanced compression are detected, while the more
subtle or initial ones are not. It is worth to discuss whether the decision of surgical
indication can be made based only on US, since only severe cases were associated with
ENMG.
Despite this association, US presented low agreement with ENMG (Kappa < 0.25) and
diagnostic measures were mostly low for any groupings used in the severity of ten
ENMG.
We agree with Fowler et al.[8] when they state that the comparison between US and ENMG cannot be considered reliable
because there is no accepted reference standard. We also emphasize that both are tests
that may be influenced by the examiner's experience in what is intended to be investigated.
We believe that decisions regarding the diagnosis of CTS can be made, initially, based
on clinical history and thorough physical examination, directed at what is intended
to be investigated.
Conclusion
We conclude that, despite the association with statistical significance between US
and more severe levels of ENMG, the two tests did not present significant agreements
for the diagnosis of CTS.
