Abstract
Objectives: To evaluate the diagnostic usefulness of high
frequency ultrasound in the management of Carpal Tunnel Syndrome among patients
suspected of having this syndrome.
Methods: Twenty- six patients
(22 women and 4 men) with a mean age of 48.5
years(range 27-70 years) suspected of having carpal tunnel syndrome were
examined by high frequency ultrasound at the middle of the carpal tunnel within
two weeks after electro diagnostic testing and included in the study. Fourteen
patients had bilateral symptoms and 12 patients had unilateral symptoms (total
40 symptomatic hands) (Twenty-six patients (five men and 21 women, mean age 38 years, range 23 71
years)). The cross- sectional area of the
median nerve was measured at the carpal tunnel. The hook of the hamate, the
pisiform bone and the flexor retinaculum were used as landmarks to margins of
carpal tunnel. The cut- off point for the cross –sectional area was chosen to
be 9.7milimetre squared. Sensitivity and
specificity of ultrasound were determined on the basis of the final
diagnosis derived from the patient's history and electromyographic studies
results which was used as the gold standard.
Results: High-frequency
ultrasound had a sensitivity of 94% and a specificity of 75%. The increased cross- sectional area of the
median nerve was the most consistent finding in 80% (32 /40) of patients, while
thickening of the flexor retinaculum was found in 25% (10/40) and tenosynovitis
of the flexor tendon in 22% (9/40). Flattening of the median nerve was present
in10% (4/40) while ganglion and swelling of the median nerve were present in
7.5% (3/40) respectively.
Conclusion: High- frequency
ultra- sonography is an effective method for the diagnosis of and may be
preferred as the first step in the assessment of carpal tunnel. Furthermore, ultrasound
may also provide information about the cause of carpal tunnel syndrome and thus
helping planning treatment and follow-up of patients.
Key wards: Carpal tunnel syndrome, Electromyography, Ultrasonography.
JRMS
September 2011; 18(3): 42-46
Introduction
Carpal tunnel syndrome (CTS) is probably
the most commonly encountered compression neuropathy in clinical practice. It
is due to compression of the median nerve as it passes through the carpal tunnel.(1)
Carpal tunnel syndrome usually affects patients between 35 and 60 years of age
and is three to five times more common
in females than males.(2) It affects 1% of the general population.(3,
4)
In most cases CTS can be diagnosed on
clinical basis.(5) The nerve conduction studies are mainly
useful in less typical cases were the diagnosis is questionable and to rule out
other causes of peripheral neuropathy.(6)
Advances in ultra-sonographic technology
had made a reliable diagnosis of CTS possible mainly based on increased cross-sectional
area (CSA) of the median nerve in the carpal tunnel.(7) It
has the advantage over the nerve conduction study in that it provides
additional information about the possible cause of CTS, such as, tenosynovitis,
rheumatoid arthritis etc.(8,9) Ultrasonographic findings correlated
well with electrophysiological tests in CTS patients.(10)
We performed this study to evaluate high-
frequency- quantitative ultra sonography (US) as a modality for the diagnosis
of CTS using the electrodiagnostic study as a reference standard.
Methods
This study was conducted at Queen Alia
Military Hospital between September 2007 and March 2008. Twenty-six patients
were included in this study (22 women and 4
men). Mean age, 48.5, range (27-70
years). Fourteen patients had bilateral
symptoms and 12 had unilateral symptoms, resulting in a total of 40 wrists were
examined. The right hand was most commonly involved. All participants had both
hands examined sonograpgically and electro- physiologically for the presence of
CTS. Clinical diagnosis of CTS was based on the American Academy of Neurology
diagnostic criteria1993.(11) A detailed history, a complete
clinical examination and baseline laboratory tests to rule out secondary causes
of CTS were done. Only patients with idiopathic CTS were included. A positive
Phalens sign was seen in 34(85%) while a positive Tinels sign was elicited in
28 wrists (70%). Tingling, numbness, and parasthesia were found in 38 hands
(95%) while atrophy of abductor pollicis and vaso-motor changes were noticed in
4 hands (10%).
Exclusion Criteria
History of underlying disease known to
cause CTS; history of previous surgery on the wrist; history of wrist fracture,
and history of steroid injection.
Electro-Diagnostic Evaluation
All subjects included in this study
underwent electro- physiologic studies by an experienced examiner according to
the protocol provided by the American Association of Electro- diagnostic Medicine
recommendations.(12) All tests were done by the same
examiner, in the same room and under similar temperature conditions.
Ultra-sonographic Examination
All patients underwent high-resolution
real time sonography of both wrists using a diagnostic Egalant sono 450 series
and 10 MHZ linear array transducer. The radiologist was blinded to the
electro-diagnostic study result. Ultrasound was done 2-14 days after the
electro-diagnostic test; the carpal bones (hook of the hamate and the pisiform)
and the flexor retinaculum were used as landmarks of the carpal tunnel. The
median nerve in the carpal tunnel was identified. Measurements in both
longitudinal and transverse planes were taken. The presence of fluid, swelling
of the median nerve, any constriction and the presence of any masses were
noted, identified and reported. The CSA of the median nerve was measured by
direct tracing with electronic calipers.
Around the margin of the nerve at the
time of the examination, the flattening ratio (the major axis of the nerve to
its minor axis) was also noted at the mid tunnel point.
Statistical Analysis
Statistical analysis was performed using
the non-Parametric U test. The CSA of the median nerve was calculated taking
the upper limit of normal cross-sectional area (CSA) of the normal
contralateral hands and other hospital staff hands. Sensitivity and specificity were calculated
on the basis of the final diagnosis determined by electro-diagnostic study
which was used as the gold standard in this study.
Results
A total of 40 symptomatic wrists in 26
consecutive patients with symptoms and signs of CTS were enrolled in this
study. Twenty– two were women and 4 were men (ratio, 11:2), their mean age was
48.5 years (range, 27-70) and the mean duration of symptoms was 4-months
(range, 1-7 months).
Table I. The clinical and electro-diagnostic findings
|
%
|
No.
of patients
|
Clinical
findings
|
|
95
85
70
10
10
|
38
34
28
4
4
|
Tingling
,numbness in median nerve distribution
Positive
phalen’s sign
Positive
Tinel’s sign
Weakness
of ABD muscle
Atrophy
of ABD muscle
|
|
|
|
Electro-
diagnostic findings
|
|
14.5
30
40
15
|
6
12
16
6
|
Normal
EMG
Mild
CTS
Moderate
Severe
|
Table II.
Ultrasound measures in 40 symptomatic hands and 12 asymptomatic hands
|
Ultrasound measure
|
Symptomatic
hands
|
Asymptomatic
hand
|
|
mild
|
moderate
|
severe
|
|
CSA(squared mm)
(mean, range)
|
9.7
8.8-11
|
10.2
9.2-11
|
11.2
9.2-13
|
7.8
4.6-9.5
|
|
Flattening ratio (square mm)
(mean, range)
|
2.4
2.2-2.6
|
2.55
2.2-2.7
|
2.7
2.5-2.9
|
2.2
2.1-2.5
|
|
|
|
|
|
|
|
CSA: cross- sectional area; FR: flattening ratio
Table III.
Causes of carpal tunnel as detected by ultra-sonography
|
Causes identified by US
|
No.
of patients
|
%
|
|
Thickening of the flexor
tendon
|
10
|
25
|
|
Tenosynovitis
|
9
|
22.5
|
|
Ganglion
|
3
|
7.5
|
|
Bifid median nerve
|
1
|
2.2
|
Electro-diagnostic findings were as follow: normal study in 6 hands (15%); mild CTS in 12 hands (30%); moderate CTS in 16 wrists (40%), and severe CTS
was found in 6 wrists (15%). Table I summarizes the clinical and the electro-
diagnostic findings in patients included in the study. In comparison with the normal hands US
assessment of the median nerve in the diseased hand showed that the CSA was
increased in 80% (32\40) wrists. Mean CSA of the median nerve was 10.2 (range,
9.2-11.7) for moderate cases of CTS and the mean CSA of the median nerve for
severe cases of CTS was 11.2 (range, 9.2-13) and the mean CSA for mild cases
was 9.7 (range, 8.8-11) while the mean CSA of the unaffected wrists was 7.8
(range, 4.6-9.5). In our study, the flattening and swelling of the median nerve
frequently being present in 4 and 3 wrists respectively, therefore, the
flattening ratio was considered not significant, although, there was a good
correlation with the severity of CTS. Table II shows the ultra- sonographic
measures in patients included in the study. Ultra-sonography helps identify local
causes of median nerve compression at the carpal tunnel and thus, may help in
planning treatment for the patient. Thickening of the flexor retinaculum was
found in 25% (10\40), tenosynovitis was elicited in 22.5 % (9\40) while
ganglion and bifid median nerve were seen in 3 and 1 patients respectively.
Table III summarizes the local causes of CTS identified by US. The patients
tolerated well the ultrasound examination. They reported no complications and
preferred this method over the electro-diagnostic testing.
Discussion
Until recently, the diagnosis of CTS was
based on a combination of positive clinical history, positive provocative tests, such as, Tinels or Phalens tests,(13-15)
combined with a positive nerve conduction study.(16)
Although, electro-diagnostic tests are still used as the gold standard to
confirm CTS, many cases of carpal tunnel syndrome may be missed, especially the
milder ones. Many authors pointed out that those conventional
electro-diagnostic tests may not be appropriate for detecting mild CTS. The
pathology causing the symptoms may be totally different from that causing delay
or abnormality on electro- physiologic test.(17) Several attempts
have been made to improve the diagnostic precision of the nerve conduction
study to improve reproducibility to minimize false-negative results in the
diagnosis, such as the incorporation of 0.3 ms difference in sensory latency
between the median and ulnar nerves or between the median and radial nerves,(18)
but still there is a high incidence of false -positive results reaching in some
reports up to 40%, as reported by Edmond MD et al.(19)
Ultra- sonographic evaluation of the
musculoskeletal system is used for the diagnosis of many disorders such as
bursitis, tendonitis, and detection of joint effusion. The concept of
neuro-radiological investigation for CTS including computed tomography (CT),
magnetic resonance imaging (MRI) and US of the wrist is evolving and gaining
more interest.(20) Ultra- sonography had been used for the
diagnosis of peripheral nerve lesions following fractures, post operatively and
during the surgical repair to describe and localize the lesion.(21)
Ultrasound is simple to handle, safe to
apply, cheap and practical and readily available tool to examine the content of
the carpal tunnel and diagnose median nerve compression.(2)
Earlier studies,(22) which used quantitative US to examine
changes in the carpal tunnel were confirmed by
studies which used MRI testing
for the same purpose.(23)
Current US criteria for the diagnosis of
CTS are: Swelling, flattening and an increase in CSA of the median nerve. The
variations in the CSA were rated corresponding to the severity of CTS.(22)
This was confirmed by our study where there is significant correlation between
CSA and severity of CTS. Our cut-off point of 9.7 for the mean CSA of the
median nerve corresponds with the previously reported findings in the
literature.(6,24,25) In comparison to the results of Wang,(26)
our study showed a sensitivity of 94% and a specificity of 75%,
In our study, further information about
the etiology of CTS was provided by US making it a better tool for patient's
evaluation and planning treatment. We recognize several limitations to our
study; firstly, we did not include a control group and the data from contralateral
asymptomatic hands and hands from hospital staffs were only used to choose our
cut-off point for the median nerve CSA. Secondly, physicians, rheumatologists
and even the radiologists lack the experience and training in the use of US in
the diagnosis of peripheral nerve lesions including CTS; therefore, they often
refrained from ordering or performing ultra-sonography. Lastly, in our study we
used the electro- diagnostic tests as the gold standard for the diagnosis of
CTS so we were unable to make a comparison with the electro- diagnostic
studies.
Conclusion
High- frequency ultra- sonography of the
median nerve and measurement of its CSA seems to be an effective tool in the
diagnosis of CTS. Ultrasound examination also provides additional information
regarding the cause of median nerve compression in the carpal tunnel that may
affect the management and future treatment planning of patients with CTS.
Finally, ultrasound examination is a safe, simple, cheap and widely available
even in district hospitals making it the preferred tool in the initial
assessment of carpal tunnel syndrome.
Acknowledgment
We would like to thank Dr Sameer Mustafa
who evaluated all the patients at the Royal Rehabilitation Centre by
electrophysiological studies.
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