Our findings indicate that the scoring of hand diagrams solely based on symptoms of 1 or 2 digits within the median nerve distribution in a population of working subjects can yield results that are similar to results obtained using the approach of Katz et al.(1)
Such scoring maximizes inter- and intra-rater reliability, minimizes time required for scoring, and predicts abnormal nerve conduction parameters when screening for carpal tunnel syndrome similar to Katz’s scoring method.
The original scoring system of the self-administered hand diagram for the diagnosis of carpal tunnel syndrome by Katz and Stirrat(1)
considers symptoms within and outside of the median nerve distribution. The presence of symptoms outside of the thumb, index, and long digits downgrades the estimated probability of carpal tunnel syndrome. In Katz’s series of patients evaluated for upper extremity paresthesia (88% prevalence of clinically diagnosed carpal tunnel syndrome), 42 of 75 patients with carpal tunnel syndrome were rated as “probable” or “possible” compared to 32 patients with “classic” diagrams (1 patient had “unlikely” diagram). This suggests that the predominance of carpal tunnel syndrome patients presented with extra-median nerve symptoms and is consistent with the 55% prevalence reported by Stevens et al.(9)
The series by Katz and Stirrat as well as another by Elfar et al(5)
document that patients with clinically diagnosed carpal tunnel syndrome almost always diagram symptoms in the median-nerve-innervated digits along with a preponderance of extra-median symptoms. In a similar fashion, our study found that symptoms outside of the median nerve distribution were common among workers with abnormal median nerve conduction values. The odds of having abnormal median nerve conduction remained nearly identical for hand diagrams scored as “possible”, “probable”, and “classic” according to Katz criteria. Thus, in our population of active workers, scoring based on the presence of extra-median symptoms (used to differentiate these ratings) failed to improve the diagram’s performance in predicting nerve conduction abnormalities in this population.
The sensitivity and specificity of hand diagram scores in predicting median nerve conduction abnormalities in a cohort of workers was lower than that reported by Katz (sensitivity: 80%, specificity: 90%).(1)
This discrepancy is likely attributable to the populations from which study cohorts were drawn. Existing literature demonstrates greater predictive ability of hand diagrams for the clinical diagnosis of carpal tunnel syndrome and nerve conduction abnormalities in clinic-based studies.(1,10,11)
It is likely that those seeking medical care are different from active workers who are symptomatic yet may not be seeking treatment. Those presenting to medical professionals with upper extremity paresthesias might be more likely to have a higher prevalence of electrodiagnostic abnormalities and more advanced degrees of nerve compression. Differences in the prevalence of electrodiagnostic abnormalities do not directly affect estimates of sensitivity and specificity but do alter the positive predictive values which would require normalization of disease prevalence for comparison between studies. Alternatively, the act of seeking care may bias physicians scoring the hand diagrams.(4)
Potentially the result of several factors, hand diagrams have demonstrated poorer predictive performance in population studies.(12–14)
There is no consensus digit identified as the most sensitive for detecting carpal tunnel syndrome. Although the index finger is commonly used to record median sensory data, different investigators have supported isolated testing of the thumb,(15)
and ring fingers(18,19)
as the most sensitive digital location. Comparing the predictive ability of single-digit scoring on the hand diagram in our study showed that the long finger out performed the index and thumb in its association with abnormal nerve conduction measurements. The specificity of these digits was similar but the long finger demonstrated superior sensitivity. This is in accord with the findings of Elfar et al(6)
who found that the long finger was subjectively the “worst” digit among patients with clinical and electrodiagnostically diagnosed carpal tunnel syndrome. Although our population cannot be assumed to have carpal tunnel syndrome, it appears that symptomatic workers with abnormal median nerve conduction parameters were more likely to diagram symptoms in the long finger than in the index or thumb. Thus, the long finger with greater sensitivity appears particularly well suited to serve as a single digit for evaluation during a first stage screening for carpal tunnel syndrome in population studies. This association may have been enhanced by measuring DSL in the long finger for this investigation, although the long finger performed well when evaluating against DML as well.
The high inter- and intra-rater reliabilities documented in this study are consistent with several prior investigations.(1,3,4)
This suggests that the scoring of hand diagrams in subsequent investigations can be reasonably performed once by a single experienced investigator. Multiple blinded ratings and duplicative ratings by additional investigators are expected to minimally impact hand diagram scores. Dale et al suggested that rater disagreement was likely related to consideration of extra-median nerve symptoms.(4)
Our data demonstrated improved reliability when only scoring symptoms within the thumb, index, and long fingers. However, reliability measures are also expected to improve when classification or grading algorithms are simpler with fewer numbers of potential categories.
There are several limitations inherent to this study. Only active workers without medically diagnosed nerve compression were enrolled in this study. Therefore, hand diagrams could not be evaluated against a true standard of subjects clinically diagnosed with, and subsequently successfully treated for, carpal tunnel syndrome. We instead have inferred accuracy in screening for carpal tunnel syndrome based upon comparisons to nerve conduction testing. Despite not using formal office based nerve conduction testing, the NC-stat device employed in this study has demonstrated criterion validity and yields comparable data in the research setting.(8,20)
To this point, the prevalence of abnormal nerve conduction testing in asymptomatic individuals within this study compares favorably to that using formal nerve conduction in a population based study.(21)
Atroshi et al identified abnormal median-ulnar differential (>0.8) in 18% of otherwise normal asymptomatic individuals while 16% of asymptomatic workers in our study had a MUD >0.5. Therefore, it is accepted that some patients will have nerve conduction results that fail to coincide with their clinical presentation. We do not presume that our results can be generalized to either patients with carpal tunnel syndrome or to those seeking medical care for upper extremity nerve complaints. When determining inter-rater reliability among individuals who routinely score such diagrams, we expect that our results represent a best case scenario and that there may be more discordant scores produced when raters are less experienced.
Hand diagram scores suggestive of carpal tunnel syndrome are associated with abnormal median nerve conduction velocities among active workers. Scoring of hand diagrams in the general population without consideration of symptoms outside of the median nerve distribution maintains the performance characteristics of the Katz scoring system while increasing the ease of use. We believe that the use of simpler scoring algorithms will aid in epidemiologic studies where notable time and effort are required to collect and score hand diagrams.