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Corticosteroid injection for the treatment of carpal tunnel syndrome
  1. S M WONG,
  2. A C F HUI
  1. Department of Medicine
  2. Prince of Wales Hospital
  3. 30–32 Ngan Shing Street
  4. Shatin, New Territories
  5. Hong Kong, China
    1. D O'GRADAIGH,
    2. P MERRY
    1. Department of Rheumatology
    2. Addenbrooke's Hospital
    3. Cambridge CB2 2QQ, UK

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      We read with interest the article by O'Gradaigh and Merry on a comparison between low and high dose, and short and long acting corticosteroids in the treatment of carpal tunnel syndrome.1 We are skeptical of the conclusion drawn by the authors that low dose steroid is as effective as high dose or long acting preparations. We calculated the 95% confidence interval for each group: group A 66% (47 to 81%), group B 63% (44 to 79%), group C 5% (0.1 to 25%), group D 72% (47 to 90%), and group E 67% (43 to 85%). Owing to the small sample size, the reported response rate cannot reliably reflect the true response rate, as illustrated by the wide confidence interval.

      The authors argued that a huge sample size was required to detect small differences between groups that might not be clinically important. However, it remains a real possibility that there is a clinical difference between treatments, which was not detected because of a type II error. Furthermore, to declare equivalence between treatments, one needs an adequate sample size with special attention to the upper boundaries of the difference in 95% confidence interval.2Failure to detect statistical difference does not imply equivalence. A large scale, probably multicentre, study may provide a definitive answer to this question.

      We are also skeptical of the suggestion that low dose steroid is potentially less toxic. The true incidence of complications related to steroid injection is not known, and discussion is mainly limited to case reports, with no specificity given for any preparations. With so few reported cases,3 one must assume they are truly rare or they have been underreported. If the assumption is the former then one will not be expecting any adverse side effects from this group of 100 or so patients.

      References

      Authors' reply

      We are pleased to have the opportunity to respond to Drs Wong and Hui. While their calculations of confidence intervals within each group are noted, it is more relevant to calculate the confidence intervals for the difference between the proportions of subjects who improve in the control and treatment groups (table 1-1). The response rates in our study for each group were very similar to those reported elsewhere, indicating that although the confidence intervals reflect the sample size, the reported response rates do reflect true rates.

      Table 1-1

      Concerning the toxicity of various steroid preparations, the animal study to which we referred has not been repeated, and clearly cannot be replicated in humans. This study was not primarily established to compare adverse effects, and we would agree that the sample was too small to detect an uncommon side effect. The implication that toxicity is rare and therefore should not be considered is unacceptable.

      The call for a larger study is inevitable when a counter-intuitive result has emerged. It cannot be assumed, as implied by Wong and Hui, that a higher dose of hydrocortisone, or the longer acting triamcinolone would have been found to be more effective but for a type II error. On the contrary, we have explained in our article how the lower dose may be sufficient to treat all steroid-responsive carpal tunnel syndrome. Those who suggest rejecting our findings, and continue to use other treatments, must (a) indicate why a higher dose or longer acting steroid should be better (bearing in mind the absence of any data to support this); (b) justify the clinical relevance of any small difference that might have been missed in this study; (c) justify the possible increased risk of (nerve) toxicity, however small—primum non nocere.

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