Article first published online: 5 OCT 2005
Copyright © 2005 by the American College of Rheumatology
Arthritis Care & Research
Volume 53, Issue 5, page 804, 15 October 2005
How to Cite
Walker-Bone, K., Palmer, K. T., Reading, I., Coggon, D. and Cooper, C. (2005), Reply. Arthritis & Rheumatism, 53: 804. doi: 10.1002/art.21462
- Issue published online: 5 OCT 2005
- Article first published online: 5 OCT 2005
To the Editors:
We appreciate the comments by Mattioli and colleagues, who observed that the population prevalence rates of CTS estimated in our recent survey are apparently low (1.2% among men and 0.9% among women) and uncommonly suggest a higher prevalence among men than among women. Mattioli et al question the validity of the UK Health and Safety Executive criteria case definitions as utilized in the Southampton examination protocol (1, 2).
For the purposes of epidemiologic research, case definitions with the greatest possible sensitivity and specificity are preferred. However, gold standard case definitions may require procedures that are costly, time consuming, or uncomfortable (e.g., electrophysiology). In this case, investigators may choose to accept case definitions with less sensitivity and specificity. Whether such case definitions are sufficiently accurate for a particular investigation depends on the effect size to be observed, the true prevalence of the disorder in the population under study, and the specific purposes of the study.
As other investigators have reported (3), we observed that symptoms of numbness or tingling occurring in the past 7 days were common among adults ages 25–64 years (982 of 4,284 hands, point prevalence 22.9%) (4). We therefore explored the anatomic distribution of these symptoms, as recorded on a hand diagram. Using different case definitions of the sensory distribution of reported symptoms, we found that symptoms that involved most of the sensory distribution of the median nerve, but not other parts of the hand, gave the best discrimination of physical risk factors widely accepted to have a causal role in CTS (e.g., forceful and repetitive movements of the wrist and hand) and, unlike other patterns of sensory symptoms, were not associated with neck pain or restriction of neck movement. In addition, and in contrast with the other patterns of symptoms, symptoms that involved most of the sensory distribution of the median nerve were not associated with lower vitality or poorer mental health (4).
The clinical case definition that we used also required a positive provocation test (a positive result of a Tinel or Phalen test) or nocturnal exacerbation. However, provocation tests have been shown to have relatively poor validity when compared with electrophysiology, with sensitivities ranging from 10% to 88% and specificities of 47–100% (5–7). As noted by one observer, conclusions from studies of these tests range from “should no longer be used in the diagnosis of carpal tunnel syndrome … patients should be referred directly for electrophysiology” to “study demonstrates a real diagnostic and prognostic value of the wrist flexion test described by Phalen” (8). Not surprisingly, these tests have the best positive predictive value for patients attending hospital clinics for surgical intervention. In the general population, however, where the prevalence of severe disease is much lower, patients and controls are more homogeneous and test performance deteriorates.
Therefore, the case definition of CTS suitable for use in large-scale epidemiologic research requires consideration. In our study, the most specific case definition was favored, at the risk of misclassifying less severe cases. It will be for other investigators to decide on their choice of more sensitive or specific case definitions, depending on the aim of their study. A key aim for all investigators, however, should be to develop a case definition that sensitively and specifically detects individuals at high future risk of needing surgical intervention for CTS, in whom appropriate preventive measures might be justified.
Karen Walker-Bone BM, MRCP, PhD*, Keith T. Palmer MA, DM, FFOM, Isabel Reading MSc, PhD, David Coggon OBE, MA, FRCP, Cyrus Cooper MA, DM, FMedSci, * Brighton and Sussex Medical School, Brighton, United Kingdom, Southampton General Hospital, Southampton, United Kingdom.