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Sensory Symptoms

Nerve conduction studies and Carpal Tunnel Syndrome


Clinical Assessment

Typical symptoms of Carpal tunnel syndrome are commonly recognisable in the history.  Symptoms are usually intermittent and occur in characteristic situations when the nerve is compressed, e.g. with a bent wrist while driving with hands on the steering wheel and other like physical activities. Symptoms often occur at night when normal lymph drainage activated by movement does not occur. Shaking of the hands, hence activating muscles, acts to improve lymph flow and takes pressure off the carpal tunnel with relief of symptoms. However, clinical assessment is not always reliable and nerve conduction studies to assess pressure on the median nerve at the wrist gives a doctor the direction to recommend the correct treatment.

Assessment with Nerve Conduction Studies

Nerve conduction studies involve stimulating a nerve, e.g. on the thumb (with ring electrodes as seen in the photograph)  and recording the response, as seen here at the wrist (with surface electrodes). The stimulus is a short lived electrical pulse which, although mildly uncomfortable, is tolerated by almost all patients without difficulty.

Carpal Tunnel SyndromeValue of Nerve Conduction Studies in Carpal Tunnel Syndrome

As expected, patients with definite Carpal tunnel syndrome with pressure on the median nerve at the wrist are more likely to have abnormal nerve conduction study results (Witt et al, 2004).

Abnormal nerve conduction studies indicative of carpal tunnel syndrome are associated with a greater chance of a successful surgical outcome (75%), compared to surgery done on clinical grounds alone with normal nerve conduction study results (51%) (Bland J, 2007).

Some argue that nerve conduction studies should be restricted to atypical cases where patients have few major clinical symptoms, atypical symptoms, or where pain is a predominant complaint (Witt et al, 2004; Wilder Smith et al, 2006). However, clinical judgement although clearly important is not always correct. Thus abnormal nerve conduction studies confirming carpal tunnel syndrome enable the patient and the doctor to progress with appropriate treatment options.
 

Treatment Response

A 75% success rate in surgical release of the Carpal tunnel is reported in patients, who are regarded as much better or cured at follow-up. However, with surgical decompression 8% of patients are worse than previously. These results reflect pooled results in more than 30,000 operations (Bland J, 2007).

Prognosis of carpal tunnel with surgery:
Complete cure or only minimal residual symptoms 75%
Slight improvement or no change 17%
Worse 8%

Prognosis of carpal tunnel with splinting of the wrist:
Complete cure or only minimal residual symptoms 30%
Slight improvement or no change 17%
Worse 0%
(Bland J, 2007).
 

References

Bland J Treatment of Carpal Tunnel syndrome Muscle nerve 2007, 36:167-171

Wilder-Smith  E  et al., Diagnosing Carpal Tunnel Syndrome – Clinical Criteria and Ancillary Tests  Neurology July 2006 Volume 2 No 7

Witt J et al.,Carpal Tunnel syndrome with normal Nerve conduction studies Muscle Nerve 2004, 29:515-522