We appreciate the interest of Drs. Hui and Wong in our recent report. We chose a 20% improvement in nocturnal paraesthesia from baseline as the primary end point because a 20% improvement is considered the primary end point in numerous controlled clinical trials, in diverse rheumatic conditions. There are no universally accepted outcome measurements in carpal tunnel syndrome (CTS), and at the time when the study began, the Disabilities of the Arm, Shoulder, and Hand questionnaire was not validated for the Spanish population. Nevertheless, the frequencies of patients showing 50% and 70% improvement were also reported and they were very similar to those showing 20% improvement.
The excellent results of the injection group, in terms of patients experiencing relapses at 12 months, can be attributed to the population studied. Our patients were all ambulatory and had a primary diagnosis of idiopathic CTS in primary care units. Thus, our patients probably had an early diagnosis and treatment, and they were not patients referred from other hospital departments, who would probably have a longer evolution of the disease and/or associated diseases. Results of local injection could have been different in more severe cases of CTS referred to secondary or tertiary care units.
To extrapolate the real-life findings at 12 months to outcomes at 18 months may be an interesting approach, but data derived from direct observation of the clinical trial is surely more valuable for obtaining clinically relevant evidence. In fact, we are focusing future investigations in this direction. We agree with Drs. Hui and Wong that longer followup and using 100% improvement as the primary outcome might have modified the conclusions of the study.