Editorial | Carpal Tunnel Syndrome: Handheld Nerve Conduction Study Devices | Which Medical Device

Carpal tunnel syndrome is a complex of symptoms including paraesthesia and muscle weakness due to compression of the median nerve.  It is one of the most commonly encountered hand conditions and has a prevalence of approximately three per cent in the general population (UK) (1).  The diagnosis is usually made on clinical grounds.  If operative intervention is being considered, nerve conduction studies can be used as an adjuvant to confirm the diagnosis although their use is somewhat controversial (2).  This is in part due to the time that they take and the associated cost.  To try and tackle this problem, portable clinic based machines have been introduced.

 

There are a number of machines available on the market in the United Kingdom.  This review aims to summarise what options are available and what differentiates them from each other.  It also summarises the limited studies available looking at each device.

 

All the devices are battery powered.  They use skin pads on the patient’s fingers and forearm to measure the function of the median nerve. They can be applied by the clinician or suitably trained nurse within the out-patient setting.  Tests can take up to twenty minutes to complete. Such devices remove the need for a visit to a neurophysiology laboratory. It is still recommended that in complex cases or where the diagnosis is unclear a qualified Neurophysiologist with the full complement of nerve conduction and electromyography studies is used.

 

The Advance TM (previously known as NC-Stat) is produced by NeuroMetrix, USA.  It provides immediate results on a hand held machine and takes approximately ten minutes to complete testing each hand.  It provides real time data on its own handheld touch screen device by testing both motor and sensory latencies.  It has been shown to be cost effective and reduce time to surgery (3).  The same study also showed no significant difference in findings between patients having portable and formal nerve conduction studies.  The device tests both the ulnar and median nerves and the manufactures also advocate its use for cubital tunnel syndrome, lumbosacral radiculopathy and diabetic peripheral neuropathy.  It provides a detailed report including waveforms and reference limits.  These have to be interpreted by the clinician in the clinic.

 

The Brevio produced by NeuMed, uses a single neurosensor to capture both motor and sensory responses for the median and ulnar nerves.  It can also be used to test motor responses for the peroneal and tibial nerves at the ankle.  It is a 4th generation product following on from the original NervePace models which tested only motor responses.  This is the model with the longest history originally described in 1984 (4).  Studies listed on the product’s website are for a number of clinical studies which included the use of the NervePace as part of the design but none confirm its diagnostic accuracy.  However, an independent literature review did not support the accuracy of the instrument and recommended against its use specifically for carpal tunnel (5).

 

Mediracer, EMG Technologies, Finland, again uses electrodes connected to a handheld device.  This device however is connected to a computer via Bluetooth and the results are transmitted over the internet to a consultant neurophysiologist for review.  A report is then compiled which is available over the internet.  It has been shown to have a sensitivity of 94% and a specificity of 98% (6).  It is reported to take 15 minutes to test both hands.  There is, however, then a wait to receive the report.  It is designed specifically for testing the median and ulnar nerves only and just assesses sensory latencies.  

 

Despite the availability of these devices and their uptake already in some hospitals, at present the BSSH do not recommend either office or laboratory based electrophysiological studies routinely (7).  They suggest studies may be indicated when there are atypical or bilateral symptoms, a suggestion of neck involvement or “double crush” syndrome, if there are persistent symptoms after surgery, if there are medico-legal or occupational indications, or in cases of diagnostic confusion.  They do not however specifically comment on portable versus standard electrophysiology.  

 

The Department of Health have published guidance on neurophysiology services.  This guide specifically mentions handheld devices and advises that their accuracy and clinical utility need to be further evaluated before being routinely used (8).

 

There are currently only limited studies confirming the diagnostic accuracy of these machines.  There is some evidence that they are cheaper than conventional studies and they clearly save time compared to waiting for conventional studies. Their use can ensure that a ‘one stop’ clinic is a viable option for the management of carpal tunnel syndrome (9,10). There routine use, however, has yet to be proven in a large multi- centre level one trial..

 

 

1. Atroshi I, Gummesson C, et al. Prevalence of carpal tunnel syndrome in a general population. JAMA. 1999;282:153–158

 

2. Jordan R, Carter T, Cummins C. A systematic review of the utility of electrodiagnostic testing in carpal tunnel syndrome. Br J Gen Pract. 2002;52:670–673

 

3. Bourke HE, et al. Clinic-based nerve conduction studies reduce time to surgery and are cost effective: a comparison with formal electrophysiological testing. Ann R Coll Surg Engl. 2011; 93(3):236-40.

 

4. Rosier, Randy N., and William F. Blair: Preliminary Clinical Evaluation of the Digital Electroneurometer. , Biomedical Sciences Instrumentation 1984; 20: 55-62.

 

5. David WS, Chaudhry V, Dubin AH, Shields RW, Jr. Literature review: nervepace digital electroneurometer in the diagnosis of carpal tunnel syndrome. Muscle Nerve. 2003; 27(3):378-385.

 

6. Tolonen U. A handheld nerve conduction measuring device in carpal tunnel syndrome. Acta Neurol Scand 2007; 115:390-397.

 

7. British Society for Surgery to the Hand. Evidence for Surgical Treatment: Carpal Tunnel Syndrome. http://www.bssh.ac.uk/education/guidelines/carpal_tunnel_syndrome.pdf (accessed 14/02/2013)

 

8. UK Department of Health. Transforming Clinical Neurophysiology Diagnostic Services to Deliver 18 Weeks. A good practice guide. August 2007

 

9. Ball C, Pearse M, Kennedy D, Hall A, Nanchahal J. Validation of a one stop carpal tunnel clinic including nerve conduction studies and hand therapy. Ann R Coll Surg Engl 2011; 93: 634-638.

 

10. Shekkeris A, Horwitz M, Ferrris B.  One stop clinic for minor hand surgery. Journal of One Day Surgery 2010; 20 (3): 58-59.