Carpal Tunnel Syndrome Workup

  • Author: Nigel L Ashworth, MBChB, MSc, FRCPC; Chief Editor: Robert H Meier III, MD   more...
 
Updated: Nov 3, 2011
 

Laboratory Studies

No blood tests exist for the diagnosis of carpal tunnel syndrome; however, laboratory testing for associated conditions (eg, diabetes) may be performed when clinically indicated.

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Imaging Studies

No imaging studies are considered routine in the diagnosis of carpal tunnel syndrome (CTS).

Magnetic resonance imaging (MRI) of the carpal tunnel is particularly useful preoperatively if a space-occupying lesion in the carpal tunnel is suggested. Signal abnormality can be detected in the median nerve in some cases of CTS, but how these abnormalities correlate to diagnosis and physiologic severity is not clear. MRI does not rule out the multitude of other differential diagnoses and is time consuming and resource intensive.[10]

Ultrasonography potentially can pick up some space-occupying lesions in the carpal tunnel. Problems differentiating the median nerve from surrounding soft tissue (particularly distally) severely limit its role in diagnosis at present.[11]

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Other Tests

Electrophysiologic studies,[12, 13, 14] including electromyography (EMG) and nerve conductions studies (NCS), are the first-line investigations in suggested carpal tunnel syndrome (CTS).[15] Abnormalities on electrophysiologic testing, in association with specific symptoms and signs, are considered the criterion standard for CTS diagnosis. In addition, other neurologic diagnoses can be excluded with these test results. NCS in a patient with CTS are seen in the images below.

Sensory nerve conduction studies from the left hanSensory nerve conduction studies from the left hand of a patient with a several-year history of numbness and weakness (responses from the median nerve in the right hand were completely absent). Note marked slowing of the conduction velocity (CV) to 29.8 and 25.5 m/s for digits 3 and 1, respectively (normal >50 m/s). The amplitude for both also is reduced markedly (normal >10). These findings are consistent with carpal tunnel syndrome. Motor nerve conduction studies from the left hand Motor nerve conduction studies from the left hand of a patient with a several-year history of numbness and weakness (responses from the median nerve in the right hand were completely absent). Note that the conduction velocity (CV) across the carpal tunnel segment slows severely to 18.3 m/s (normal >50 m/s) and that the distal motor latency is prolonged at 6.3 ms (normal < 4.2 ms). Amplitudes are low for the wrist and elbow stimulus sites at 4.7 mV (normal >5 mV), but amplitudes are 31% higher distal to the carpal tunnel (at the palm). This discrepancy may represent conduction block (neurapraxia) at the level of the carpal tunnel or coactivation of the ulnar branch to adductor pollicis. Needle electromyography is required to determine whether axonal loss is present.

Electrophysiologic testing also can provide an accurate assessment of how severe the damage to the nerve is, thereby directing management and providing objective criteria for the determination of prognosis. CTS is usually divided into mild, moderate, and severe; however, criteria for this assessment usually vary from lab to lab. In general, patients with mild CTS have sensory abnormalities alone on electrophysiologic testing, and patients with sensory plus motor abnormalities have moderate CTS. However, any evidence of axonal loss (eg, decreased or absent sensory or motor responses distal to the carpal tunnel or neuropathic abnormalities on needle EMG) is classified as severe CTS.

Changes in electrophysiologic results over time can be used to assess the success of various treatment modalities.

The American Association of Electrodiagnostic Medicine has published standards and guidelines that govern the minimum number of studies that should be performed to diagnose CTS.[13]

Other quantitative tests, such as thermography and vibrometry, have been shown to be inferior to electrophysiologic examination and, because they have not been supported by controlled studies, are not recommended.

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Contributor Information and Disclosures
Author

Nigel L Ashworth, MBChB, MSc, FRCPC  Professor and Chief, Division of Physical Medicine and Rehabilitation, Glenrose Rehabilitation Hospital, University of Alberta

Nigel L Ashworth, MBChB, MSc, FRCPC is a member of the following medical societies: American Association of Neuromuscular and Electrodiagnostic Medicine, Australian & New Zealand Association of Neurologists, British Medical Association, Canadian Association of Physical Medicine and Rehabilitation, Canadian Medical Association, Canadian Society of Clinical Neurophysiologists, and Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Specialty Editor Board

Benjamin M Sucher, DO, FAAPMR, FAOCPMR  Medical Director, EMG Labs of AARA (Arizona Arthritis & Rheumatology Associates)

Benjamin M Sucher, DO, FAAPMR, FAOCPMR is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Association of Neuromuscular and Electrodiagnostic Medicine, American Osteopathic Association, and American Osteopathic College of Physical Medicine and Rehabilitation

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Patrick M Foye, MD  Associate Professor of Physical Medicine and Rehabilitation, Co-Director of Musculoskeletal Fellowship, Co-Director of Back Pain Clinic, Director of Coccyx Pain Service (Tailbone Pain Service: www.TailboneDoctor.com), University of Medicine and Dentistry of New Jersey, New Jersey Medical School

Patrick M Foye, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Association of Neuromuscular and Electrodiagnostic Medicine, Association of Academic Physiatrists, and International Spine Intervention Society

Disclosure: Nothing to disclose.

Kelly L Allen, MD  Medical Director, Medevals

Disclosure: Nothing to disclose.

Chief Editor

Robert H Meier III, MD  Director, Amputee Services of America; Active Medical Staff, Presbyterian/St Luke's Hospital, Spalding Rehabilitation Hospital, Select Specialty Hospital; Consulting Staff, Kindred Hospital

Robert H Meier III, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation and Association of Academic Physiatrists

Disclosure: Nothing to disclose.

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The hands of an 80-year-old woman with a several-year history of numbness and weakness are shown in this photo. Note severe thenar muscle (abductor pollicis brevis, opponens pollicis) wasting of the right hand, with preservation of hypothenar eminence.
Sensory nerve conduction studies from the left hand of a patient with a several-year history of numbness and weakness (responses from the median nerve in the right hand were completely absent). Note marked slowing of the conduction velocity (CV) to 29.8 and 25.5 m/s for digits 3 and 1, respectively (normal >50 m/s). The amplitude for both also is reduced markedly (normal >10). These findings are consistent with carpal tunnel syndrome.
Motor nerve conduction studies from the left hand of a patient with a several-year history of numbness and weakness (responses from the median nerve in the right hand were completely absent). Note that the conduction velocity (CV) across the carpal tunnel segment slows severely to 18.3 m/s (normal >50 m/s) and that the distal motor latency is prolonged at 6.3 ms (normal < 4.2 ms). Amplitudes are low for the wrist and elbow stimulus sites at 4.7 mV (normal >5 mV), but amplitudes are 31% higher distal to the carpal tunnel (at the palm). This discrepancy may represent conduction block (neurapraxia) at the level of the carpal tunnel or coactivation of the ulnar branch to adductor pollicis. Needle electromyography is required to determine whether axonal loss is present.
 
 
 
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