Prospective analysis of the accuracy of diagnosis of carpal tunnel syndrome using a web-based questionnaire

Abstract

Objective: To confirm the accuracy of a diagnostic questionnaire for carpal tunnel syndrome (CTS) when presented via a public website rather than on paper.

Design: Prospective comparison of the probability of CTS as assessed by the web-based questionnaire at http://www.carpal-tunnel.net with the results of nerve conduction studies.

Setting: Subregional neurophysiology laboratory serving a population of 700,000 in East Kent, UK.

Participants: 2821 individuals who were able to complete an online diagnostic questionnaire out of 4899 referred for initial diagnostic testing for new presentations with suspected CTS from April 2011 to March 2013. No exclusions were made on grounds of age, gender or coincident pathology. Main outcome measure--nerve conduction results confirming CTS. The severity of median nerve impairment demonstrated was also assessed using a validated neurophysiological scale.

Results: The web-based questionnaire accurately estimates the probability of CTS being confirmed on nerve conduction studies. Using a website diagnostic score of ≥40% as an example cut-off value the questionnaire achieves 78% sensitivity and 68% specificity in predicting the finding of evidence of CTS on nerve conduction studies. The web-based version of the diagnostic questionnaire was as accurate as the original paper version with an area under the receiver operating characteristic curve of 0.79. There was also a significant correlation between the diagnostic score given by the website and the severity of CTS with higher scores being associated with greater nerve dysfunction (r=0.3, p<0.00001).

Conclusions: Completion of the symptom questionnaire on the website by patients at home provides a prediction of the likelihood of CTS which is sufficiently accurate to be used in initial planning of investigation and treatment.

Keywords: Carpal Tunnel Syndrome; Diagnosis; Questionnaire; Sensitivity and Specificity; World Wide Web.

Figure 1

Receiver operating characteristic curve illustrating the diagnostic sensitivity and specificity of the website questionnaire for neurophysiologically defined carpal tunnel syndrome with varying cut-off scores from 0% to 100% (diamonds—WEB). For comparison the equivalent curve for the paper version of the questionnaire is shown (circles—ANN4). The area under these curves is 0.79. The diagonal line would indicate a test with no ability to discriminate between disease and normal.

Figure 2

The relationship between the website score and the severity of carpal tunnel syndrome (CTS) demonstrated in the worst hand. Each column shows the proportions of patients in one 10% range of website diagnostic scores who proved to have nerve conduction studies (NCS) of each grade of severity, normalised to 100%. Thus, of 401 patients with a website diagnostic score of <10%, 87% had normal NCS, 4% grade 1, 4% grade 2, 2% grade 3, 0.2% grade 4, 1% grade 5 and 0.2% grade 6.

Figure 3

Distributions of website diagnostic scores (in 10% bands) in patients who attended for testing (white bars), compared to those who failed to attend (black bars). CTS, carpal tunnel syndrome.

Figure 4

STARD flow diagram for the study using an arbitrary cut-off score on the website questionnaire of 40% as indicating carpal tunnel syndrome. CTS, carpal tunnel syndrome; NCS, nerve conduction studies.