G u i d i n g Tre a t m e n t f o r

C a r p a l Tu n n e l S y n d ro m e
Leilei Wang, MD, PhD

KEYWORDS
 Carpal tunnel syndrome  Neuropathy  Nerve conduction studies
 Electrodiagnosis

KEY POINTS
 Making the correct carpal tunnel syndrome diagnosis is the most important step in treat-
ment. Electrodiagnosis can confirm carpal tunnel syndrome and eliminate mimicking dis-
eases from the differential.
 Treatment should provide satisfactory pain relief and protection of the median nerve from
further deterioration.
 The importance and value of reversing focal median mononeuropathy at the wrist in the
long term have not been sufficiently addressed, despite its high prevalence and chronic
nature.
 Only electrodiagnosis provides information on focal median mononeuropathy at the wrist
that could be used to classify carpal tunnel syndrome from mild to severe.
 False positives can cause more harm than false negatives in the case of carpal tunnel
syndrome.

INTRODUCTION

Carpal tunnel syndrome (CTS) has long been accepted to be a symptomatic condition
caused by compression of the median nerve at the wrist. Historically, the realization
that CTS is a clear clinical entity resulting from 1 nerve affected at 1 specific anatomic
location took time.1 Medical understanding of CTS as a focal median mononeuropathy
at the wrist (FMMNW) was well-established by the mid-20th century.2,3 Surgeons
treating traumatically injured upper limbs were early pioneers of this field.4
Known as the most common focal entrapment mononeuropathy, CTS represents
90% of all entrapment neuropathy and affects millions of Americans. One in 5 ambu-
latory clinic visits are for CTS, with a reported high incidence and prevalence not only
in the United States but in other countries as well. The lifetime risk is estimated to be
10%.5–8 Both clinicians of general practice and neuromusculoskeletal specialties see,

Disclosure: None.
Department of Rehabilitation Medicine, School of Medicine, University of Washington, 1959
Northeast Pacific Street, Box 356157, Seattle, WA 98195, USA
E-mail address: lw7@uw.edu

Phys Med Rehabil Clin N Am - (2018) -–-

https://doi.org/10.1016/j.pmr.2018.06.009 pmr.theclinics.com
1047-9651/18/ª 2018 Elsevier Inc. All rights reserved.
2 Wang

diagnose, and treat patients with CTS by recognizing its constellation symptoms and
signs and using provocative test, electrodiagnosis (EDX) and more recently imaging
modality including computer tomography, magnetic resonance neurography and ul-
trasound examination.9–14
EDX for the diagnosis of CTS has had much in-depth investigation and collective
knowledge accumulated since the 1950s.15 It is especially helpful when the clinical
presentation is less straightforward.16,17 Diagnostic validity has been extensively stud-
ied with continuous research interest for further improvements, including the recently
published article addressing diagnostic normal values that entailed group consensus
and an extensive review of the literature.18
Because CTS is such a common and often chronic disease, it has provided physi-
cians and researchers ample opportunities for refining medical treatments and sharing
cumulative experiences. There is an impressive volume of literature that is still growing
with technological advancements and ongoing academic research. The treatment of
CTS, which is typically splinting, corticosteroid injection, and surgery, have been
mostly effective.19,20 Published practice guidelines for treating CTS including the
recent guideline by the American Academy of Orthopedic Surgeons, which are
endorsed by medical professional organizations including the Academy of Physical
Medicine and Rehabilitation and the American Association of Neuromuscular & Elec-
trodiagnostic Medicine.21
However, there remain plenty of variations of management with room for discussion
and improvement.22–24 The goal of this article is to review the current literature on
the diagnosis and management of CTS, with an emphasis on the role of EDX when
treating CTS.

ANATOMY OF THE CARPAL TUNNEL AND MEDIAN NERVE

To understand current CTS treatment practice, a review of median nerve and carpal
tunnel anatomy is important. The carpal tunnel is a shallow, U-shaped, bony trough
formed by the carpal bones, with the transverse carpal ligament enclosing the open
volar side. The carpal tunnel is an inelastic and narrow passage for the median nerve
and 9 flexor tendons to travel from the forearm to the hand. The slightly dumbbell-
shaped carpal tunnel has a width of 20 to 25 mm. The segment of median nerve trav-
eling inside the carpal tunnel between the levels of the distal wrist flexion crease and
the proximal metaphysis is at high risk of becoming entrapped and injured.25–27
The median nerve is formed by fascicles from the medial and lateral cord of the
brachial plexus. After reaching the elbow, the median nerve sends motor axons to
innervate several muscles: the pronator teres, flexor carpi radialis, palmaris longus,
and flexor digitorum superficialis. Then, the anterior interosseous nerve branches
off, which innervates the flexor digitorum profundus I and II, the flexor pollicis longus
and the pronator quadratus muscles. There are several known sites in the arm and
forearm that could entrap the median nerve, but these occur with a much lower fre-
quency than at the carpal tunnel. The palmar cutaneous branch of the median nerve
piercing through the fascia provides skin sensation of the proximal palm. The remain-
ing median nerve fascicles reach the wrist between the tendons of flexor carpi radialis
and palmaris longus and enter the carpal tunnel.
The terminal branches of the median nerve have several proper digital sensory
nerves and 1 motor nerve. The proper digital nerves provide sensation to the palmar
skin of the thumb, index, and the long and radial sides of the ring fingers, plus the dor-
sal skin of the distal phalanx of these digits. The terminal motor branch was named the
recurrent or thenar nerve because it makes a turnaround in the palm before arriving at
 Guiding Treatment for Carpal Tunnel Syndrome 3

the thenar eminence and innervating the abductor pollicis brevis, opponents pollicis,
superficial head of the flexor pollicis brevis muscles.
CTS develops when the median nerve is compressed and clinical symptoms occur
in the distribution of the anatomy of these terminal branches. Clinical complaints and
physical findings in the median nerve distribution are the foundation when diagnosing
CTS. However, many sensory and motor anomalies exist. It is beyond the scope of this
article, but a keen awareness of these anomalies is important not only to CTS surgery
performing carpal tunnel release (CTR) but also to the diagnosis of CTS.28–30

CAUSES AND DIAGNOSIS OF CARPAL TUNNEL SYNDROME

Consensus on the cause of the most common idiopathic CTS has been compression
and ischemic insult to the short segment of median nerve inside the carpal tunnel.
Normal carpal tunnel pressure is less than 5 mm Hg with the wrist in neutral position.
Pressure increases with activity and prolonged flexion and extension. For example, it
increases to 20 to 30 mm Hg with the use of a computer mouse. Impaired median
nerve blood flow occurs at the pressure of 20 to 30 mm Hg. When the median nerve
is stressed beyond its physiologic tolerance, CTS symptoms develop.31,32 Nerves do
not like compression or ischemia. With high enough pressure, long enough duration,
and associated ischemia, the median nerve begins to develop pathology. The result is
FMMNW with sensory demyelination being first, followed by motor demyelination, and
eventually sensory and motor axon loss. Risk factors include high body mass index,
female gender, age, pregnancy, and many others.33–35 Stretching and tethering by
the surrounding connective tissue like thickened or swollen synovia or bony irregularity
are other plausible causes of compression that results in ischemic injury.
Although CTS can resolve spontaneously, it is common for patients diagnosed with
CTS to recall similar symptoms in the past with either a gradual worsening or a
relapsing–remitting pattern over months, years, or even decades. The most frequent
complaints are nighttime burning and “pins-and-needles” pain in the fingers. Acropar-
aesthesiae is used to describe these sensations.3 As CTS progresses, pain and numb-
ness is typically felt during the day intermittently, triggered by activities like driving,
lifting, or computer use. In many patients, the pain eventually becomes constant. Pa-
tients report feeling of swollen hand, clumsiness, and object dropping. Weakness is a
late sign associated with thenar atrophy.
Less typical sensory symptoms are frequently reported by many patients, which
range from symptoms involving all the fingers, entire hand, forearm, arm, and shoul-
der. Nonmedian nerve distribution neurologic symptoms alone should not deter one
away from CTS suspicion.36,37
Pain is a prominent feature of CTS and may limit sensation and strength examina-
tion. Adding visual inspection, noting subtle differences when comparing the affected
hand with the asymptomatic hand (taking hand dominance into consideration) can be
helpful to determine if strength limitations are related to pain or muscle loss.
Many provocative special tests are available.10,11,38 Besides the classic Tinel and
Phalen test, there are many others described in the literature.39,40 Most are designed
to apply stress to the median nerve at the wrist in an attempt to provoke CTS symp-
toms. These tests could be performed quickly in an ambulatory clinic. The reported
sensitivity and specificity of these maneuvers has been variable.41 Fortunately,
when used consistently, and coupled with relevant clinical history and physical exam-
ination that includes searching for both the pertinent positive and the pertinent nega-
tive information, a diagnosis of CTS can be achieved with reasonable certainty in many
CTS cases.
4 Wang

Magnetic resonance neurography and ultrasound imagining can provide additional

information such as synovitis and anatomic anomaly.42,43 In contrast, computed to-
mography—despite its strength in viewing bones—was reported to have little value.44
EDX has been called “the gold standard,” when in reality a gold standard does not
exist in diagnosing CTS. The use of EDX for CTS has some shortcomings, including a
relatively low sensitivity, causing patient discomfort, and the potential of increasing
costs. However, many treating physicians and patients appreciate the extra informa-
tion it provides regarding the diagnosis when making decision on treatment, and also
for prognosis.45 In contrast, imaging studies provide, for the most part, binary data:
differentiating a normal versus abnormal appearing median nerve, whereas EDX
further provides quantifiable information on the pathology of FMMNW. Although
EDX is not necessary to diagnose CTS, its use for confirmation and eliminating other
causes are valuable.
Diagnosing CTS becomes more challenging in a patient with diabetes, neck or
shoulder pain extending to hand, or traumatic upper limb injuries. EDX is helpful in
the diagnosis of peripheral polyneuropathy, cervical radiculopathy, plexopathy,
and proximal median mononeuropathy, which can all cause symptoms similar
to CTS.

TREATMENT, OUTCOME, AND USEFULNESS OF ELECTRODIAGNOSIS

Treatments are typically grouped into conservative treatments versus surgical treat-
ments. The 2 approaches that have resulted in the most consistent satisfaction are
steroid injection and CTR.5,9 Available treatment outcome research favor steroid injec-
tion and surgery.46,47 Splints used as adjunct treatment seem to improve pain in many
patients despite having no significant statistical evidence by Cochrane analysis.48 Be-
sides pain reduction and sleep improvement, splint use helps some patients to
become more ergonomically aware of their hand use while deciding on the treatment
based on their individual needs or waiting to be seen by a hand specialist. Some pa-
tients afflicted by CTS prefer to delay surgery or avoid it all together. The newest treat-
ment, hydrodissection or transverse carpal ligament release under ultrasound
guidance by nonsurgical physicians, is showing promise with research evidence yet
to come.49
Studies have shown that there seems to be a window for optimal treatment out-
comes. Conservative treatments are less effective in reducing CTS symptoms when
used for advanced moderate or severe cases. Surgical outcomes are also better in
resolving CTS symptoms and the underlying FMMNW when performed for the mild
or early moderate CTS.
Has EDX added usefulness in guiding CTS treatment? The author would be the first
to point out the potential biases from a skewed viewpoint. Yet, with more than 500
CTS study cases annually in a teaching University EDX laboratory, clinic-based obser-
vations could offer some insights. See Table 1 for examples of how EDX adds value to
clinical care.
CTS and FMMNW are often used as synonyms; however, there are some differ-
ences, because a syndrome is about symptoms, whereas EDX-positive CTS is
more specifically for FMMNW. Trying to predict the severity of FMMNW using CTS
symptoms can be misleading. Abnormal EDX findings do not always parallel the
severity of CTS symptoms. There are patients with classic CTS symptoms but normal
EDX. Abnormal EDX findings are also found in asymptomatic population.50 The
disparity between symptoms and electrodiagnostic findings can even be seen within
the same patient when bilateral studies are performed. Surgery, referred to as the
 Guiding Treatment for Carpal Tunnel Syndrome 5

Table 1
Ways that EDX adds value in the diagnosis and treatment of CTS

Example of Change in
Reason Example of Situation Management
Confirm/refute suspected Patient with hand pain at night Negative EDX may lead to
diagnosis diagnosis of hand OA or
tendinopathy as cause of
symptoms
Lead to additional Patient with hand numbness is Search for causes of
diagnoses found to have polyneuropathy polyneuropathy could lead
with or without CTS to diagnosis of Diabetes,
Vitamin deficiency, etc.
Find other causes of Patient with hand numbness Treatment of radiculopathy
symptoms found to have cervical
radiculopathy
Pre-CTR data compared Patient has recurrent symptoms EDX confirms worsening
with post-CTR data after CTR FMMNW and patient treated
appropriately OR EDX finds
improvement in FMMNW
and another etiology sought
Guide treatment Patient has evidence of Physician does not continue
worsening FMMNW conservative treatment with
night splints, but moves to
surgical referral
Prognosis Electrodiagnostic category Patient makes informed
used to inform discussion decision about whether to
about prognosis with surgery move forward with elective
surgery
Research EDX confirms diagnosis (“gold Patients appropriately
standard”) categorized for study and
follow-up

Abbreviations: CTR, carpal tunnel release; CTS, carpal tunnel syndrome; EDX, electrodiagnosis;
FMMNW, focal median mononeuropathy at the wrist; OA, osteoarthritis.

“definitive treatment” for CTS, has been shown to relieve CTS symptoms ranging from
the EDX-negative group to the group with no recordable median nerve signal.45,51
Therefore, if the goal is only to cure the symptoms, in cases where the diagnosis is
certain, EDX may be unnecessary.
In contrast, EDX adds values in several ways. There is evidence that EDX can be
used in predicting outcomes for both the steroid injection and CTR.52–56 It is also help-
ful in differentiating mimicking diseases like overuse tendonitis, cervical radiculopathy,
peripheral neuropathy, and misleading indicators in cases of trauma.
Having had a pre-CTR EDX study can be helpful when studying the post-CTR symp-
tomatic group. Abnormalities of EDX study improve after CTR. Pre-CTR electrodiag-
nostic studies are helpful for comparison; even with complete resolution of CTS
symptoms, residual EDX abnormality often persist, unless the study result was normal
or only mild abnormal before surgery. Post-CTR median motor latencies often return
to normal, but the sensory latencies often do not. Absent sensory response on pretest-
ing may return, but the amplitude is often small. The underlying reasons for residual
sensory abnormality are not clear but could be because the sensory nerves typically
have worse demyelination than motor fibers, and therefore sensory nerve remyelina-
tion is less efficient after release. Sensory axon loss could be another mechanism
6 Wang

resulting in the residual abnormality given large and fast conducting nerve fibers are
more vulnerable to compression and ischemia.
It is important to point out that although current CTS classification schemes differ in
details, they all use EDX findings of FMMNW. Researchers use EDX as a tool or an
assay to compare pretreatment and posttreatment conditions of CTS.

LOOKING INTO THE FUTURE

Continued Attention to Sensitivity in Making the Diagnosis
The low sensitivity of EDX should be addressed by using the best-published normal
values for diagnosis as recommended by the American Association of Neuromuscular
& Electrodiagnostic Medicine and using diagnostic criteria less influenced by intrinsic
or extrinsic variations. Comparative values are preferred when available over the use
of population normal values for making the diagnosis. This is because mild abnormal-
ities can be detected with less influences and potential errors introduced by temper-
ature and other factors. Findings are also more reproducible with interexaminer
studies.
Attention to Sensory Amplitudes, Not Just Latency
There are patients who seem to have early median sensory axon loss in addition to
sensory demyelination, showing decreased or even absent sensory amplitude while
median motor results are well within the normal range. Closer attention to sensory
amplitude in addition to sensory latency may be useful in better stratifying CTS for
prognosis and outcome research.
Inching and Other Techniques
Short distance nerve conduction studies have been used to measure entrapment neu-
ropathy. This test is used most frequently in the upper limb for the evaluation of ulnar
neuropathy at the elbow. There are a few publications on applying inching and other
techniques for the study of CTS.57–59 This test should be revisited and standardized.
The author has found it to be valuable in determining the location of median neurop-
athy in patients with a history of forearm injury in search of treatable CTS.60
Clinical Skills and Sound Medical and Technical Knowledge of Electrodiagnosis
over Templates and Inflexible Protocols
Clinical skills guide the electrodiagnosticians to choose properly among many estab-
lished study options and increase the validity when interpreting findings for the individ-
ual patient.
Decreasing Patient Discomfort
The associated discomfort of EDX should be decreased. Skilled examining physicians
take their time to explain the query (the why) and the study approach (the what) while
answering questions and providing the education to the patient that he or she needs.
Discomfort extent reported by the patient differs greatly with needle examination
generally being the worst, followed by motor conduction study with sensory conduc-
tion study being the least bothersome. However, not infrequently, the patient being
tested falls asleep during the study in our laboratory. Attention to each patient’s indi-
vidual and unique concerns is important. In addition to using good EDX techniques,
making clear to patients that they can stop their study at any time could be valuable
while using reassuring and understanding mannerisms. In the author’s experience,
essentially no one declines to begin the study, and only a few per year opted to
stop. Most of these patients rescheduled and completed the study at the second
 Guiding Treatment for Carpal Tunnel Syndrome 7

appointment. Conveying knowledge and respect to variable individual tolerance

lightens patient’s anxiety and worries of “being weak” or even feeling of shame.
Many patients are surprised at the ease of the study, with some lamenting their unnec-
essarily lost sleep the night before from reading information about EDX on the Internet.
Pain, fear, and coping capacity with a stressful condition vary greatly from person to
person depending on the individual’s biology, personality, past experiences, and
many other factors. Diagnosing and treating CTS can serve as a reminder for profes-
sionals to do the best for each patient and to add no harm.
Better Carpal Tunnel Syndrome Outcome Research
Conducting outcome and outcome comparison studies are time consuming and
manpower expensive. Numerous variations, including biology, milieu, experience,
and style in seeking medical advice are difficult to control fully. Treating clinicians
are likely, often unintentionally, to introduce bias depending on professional training
and practice. Currently, most long-term prospective outcome research followed
CTS and treatments evaluate this over a few months to a couple of years at most.
Outcome studies for a longer period of time will likely be important, not only for
choosing treatment options but also from a public health management standpoint
given the lifelong risk and the chronic nature of CTS.
Better Prevention and Early Management
Physicians should consider managing CTS similarly to other epidemic and chronic dis-
eases by using education and routine quick checks at regular health visits. With a
decrease in the individual’s risk of developing CTS and early diagnosis using EDX
as indicated, the disease burden of CTS and its associated high medical treatment
cost, personal life quality, or work productivity loss could be decreased.61,62

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