Department of Rheumatology, Craigavon Area Hospital, 68 Lurgan Road, Craigavon BT63 5QQ, UK
SIR, Carpal tunnel syndrome (CTS) is the most common nerve entrapment disorder and is a frequent diagnosis made in rheumatology. It is characterized by pain and paraesthesia and may ultimately lead to muscle wasting of the hand. The diagnosis of this disorder is often clinical with nerve conduction studies (NCS) as a diagnostic aid. We wished to assess whether NCS were beneficial in aiding diagnosis and treatment in CTS.
We studied 40 patients who attended the rheumatology out-patient clinic with symptoms consistent with possible CTS between May 2000 and November 2001. Clinical data were obtained from their records, and a telephone questionnaire regarding outcome of treatment, 6 months post-injection, was completed. All patients had NCS performed at the same centre and reported by the same neurophysiologist. Each injection was performed by the same physician using the same technique with 8 mg of Depo-medrone. The results of NCS were categorized into normal, borderline delay or definite delay of median nerve conduction.
In total, 47 injections were performed, which included seven repeat injections. Eight patients (20%) had definite median nerve delay on NCS, and six of these patients benefited from injection, the other two requiring surgery. We found that clinical signs and symptoms in this group were consistent with the diagnosis of carpal tunnel syndrome. Twenty-four patients (60%) had borderline delay of median nerve conduction on NCS, and nine of these benefited after the first injection and a further seven after repeat injection, resulting in resolution of symptoms after injection in 16 of our patients. Of the other eight patients who did not benefit, four have had surgery with benefit and the other four await surgical opinion. In this group there was a wide range of clinical signs and symptoms, which could not be correlated to whether the patient benefited from injection. Eight patients (20%) had normal NCS and yet six of these patients benefited from injection; the other two did not. The symptoms and signs in this group were non-specific. There were only three reported complications, which were due to bruising around the injection site. The main discerning symptoms and signs in our group of patients were tingling in the fingers at night, weakness of thumb abduction and sensory loss over the median nerve distribution.
Our results would suggest that if the symptoms and signs confirm carpal tunnel syndrome, NCS did not add to the diagnosis but only delayed therapy10 weeks on average in our study group. Previous studies of NCS have shown false-negative results ranging from 8 to 18% [14]. It is postulated that this is because CTS can be an intermittent problem, may be due in part to small unmyelinated fibres that the test cannot detect, or that in the early stages of the disease the test is normal. Vague symptoms and signs warrant NCS, but our results to date show that 32 of our patients (80%) had borderline/normal NCS, and yet 22 of these patients benefited from injection. Previous reports have cited that over 90% of patients have initial relief of pain following injection, and in our study 70% of patients benefited. Reports of long-term benefit are more variable and range from 20 to 90% [57]. These results correlate with the argument that electrodiagnosis delays treatment and should be reserved for those patients who do not respond to injection, or before surgery, and that clinical diagnosis should be relied on. These patients will be followed up to assess recurrence rates.
Notes
Correspondence to: S. A. Wright, Rheumatology Department, Musgrave Park Hospital, Stockman's Lane, Belfast BT9 7JB, UK. E-mail: stephen{at}wright866.fsnet.co.uk
References
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