From the MRC Environmental Epidemiology Unit, University of Southampton, Southampton, England.
Received for publication May 14, 2002; accepted for publication September 30, 2002.
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ABSTRACT |
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carpal tunnel syndrome; diagnosis; paresthesia
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INTRODUCTION |
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In theory, the anatomic distribution of numbness and tingling in the hand should provide a useful pointer to the underlying pathology. For example, symptoms associated with carpal tunnel syndrome would be expected to occur in the sensory distribution of the median nerve (i.e., on the palmar surfaces of the thumb, index finger, middle finger and medial part of the ring finger, and in the medial palm). In practice, however, the distinction may not be clear-cut. Thus, sensory disturbance that is limited to the palmar surface of the index finger might be attributable to either carpal tunnel syndrome or impingement of the C7 nerve root. Moreover, recall of the exact distribution of symptoms may not always be reliable.
Despite these limitations, if the reported anatomic pattern of numbness and tingling discriminates sufficiently between two or more underlying pathologies in the neck or arm, this could be useful in the design of epidemiologic surveys. For example, the distribution of symptoms might be used as a criterion in the selection of subsets of subjects for clinical investigations, such as nerve conduction studies, where these were not practical in a full study sample.
To explore the potential for such discrimination, we have examined the patterns of numbness and tingling in the hand that were reported in a survey of adults from the general population and compared their associations with neck pain, psychosocial variables, and occupational activities.
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MATERIALS AND METHODS |
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Among other things, the questionnaire asked about demographic details, physical activities in the subjects current job, and the occurrence of pain in the neck or arm and of numbness or tingling in the hand during the past 7 days. It also included sections from the Medical Outcomes Study 36-item Short-Form Health Survey (SF-36) relating to vitality and mental health (1).
Completed questionnaires were returned by 6,038 (62 percent) of the subjects mailed, of whom 3,152 (52 percent) reported pain or sensory symptoms in the arm or neck. Subsequently, all of the symptomatic responders were invited to undergo interview and physical examination, together with a random sample of 489 men and women who had no symptoms. In total, 2,145 (59 percent) agreed (1,960 (62 percent) of those with symptoms and 185 (38 percent) of those who were asymptomatic).
The interviews and examinations were carried out by four trained research nurses and a research physiotherapist, at a median interval of 37 days (range, 0398 days; 90 percent within 108 days) after return of the initial questionnaire. At the interview, subjects were again asked about recent symptoms in their neck and arm. In particular, a note was made of whether, during the past 7 days, they had experienced numbness or tingling, lasting at least 3 minutes, in any of the regions of the hand depicted in figure 1.
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Statistical analysis was based on 854 men and 1,288 women (three subjects were excluded because of missing information on the distribution of numbness and tingling in the hands). Symptoms were classified according to the history elicited at interview (by the time of interview, 606 subjects who reported symptoms in response to the postal questionnaire had become asymptomatic, and 27 who previously were symptom free had developed symptoms), and the algorithm described in figure 1 was used to distinguish different anatomic patterns of numbness and tingling in the hands. Mental health, vitality, and occupational activities were derived from the postal questionnaire. Associations between hand symptoms and other variables were examined by log-logistic regression and summarized by prevalence ratios with 95 percent confidence intervals.
Ethical approval for the study was obtained from the Southampton and Southwest Hampshire Research Ethics Committee.
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RESULTS |
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At the time of interview and examination, numbness or tingling was reported to have occurred during the past 7 days in 982 of 4,284 hands. These included 92 hands in which the symptoms were restricted to the median nerve distribution, and within this subset, the extent to which the palmar surfaces of the thumb, index finger, and middle finger were involved showed a distinctive pattern. Most often, symptoms affected from one to three of regions 2229 in figure 1 (52 hands) or 68 regions (34 hands). Therefore, in subsequent analyses, a distinction was drawn between "extensive median" symptoms that involved at least six of regions 2229 and "limited median" symptoms that were confined to between one and five of these regions.
Table 1 summarizes the frequency with which different anatomic distributions of numbness and tingling were reported in each hand. Overall, the most common patterns were "mixed" (10.2 percent of hands) and "all fingers" (6.0 percent). In comparison, extensive median symptoms were rare (0.8 percent). Both Phalens and Tinels tests were positive most often in hands with extensive median symptoms (59 percent and 18 percent, respectively), whereas the prevalence of positive tests in hands with limited median symptoms (29 percent and 7 percent) was lower than in hands with numbness or tingling in other distributions (i.e., nonmedian, all fingers, and mixed) (36 percent and 10 percent).
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DISCUSSION |
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The phased approach that we adopted to data collection meant that subjects could be lost from the investigation at two stages. However, we think that the incomplete response is unlikely to have been a major source of bias in relation to the associations that we examined. For example, even if symptomatic subjects responded more readily than those without symptoms, as is plausible, this would not bias comparisons between different patterns of numbness and tingling in the hand unless there was differential overrepresentation of people with a specific distribution of sensory disturbance in combination with an associated symptom, physical sign, or risk factor.
A more likely source of error was inaccuracy in the reporting of symptoms. Even when recall is only over a maximum of 7 days, it may be difficult to remember exactly which parts of the hands have been affected by numbness and tingling. In general, any resulting misclassification of symptoms would be expected to blur distinctions between different patterns of anatomic involvement.
Perhaps the most common cause of persistent numbness and tingling of the hand in the general population is compression of cervical nerve roots as a consequence of cervical spondylosis. In support of this, we found that sensory disturbance in the hand was associated with neck pain, particularly if there was also restriction of neck movements (table 3). It is notable, however, that these associations did not extend to numbness and tingling with an extensive median distribution, which suggests that this specific pattern of sensory symptoms does not commonly arise from pathology in the neck.
Also in contrast to other patterns of numbness and tingling, extensive median symptoms were not associated with low vitality or poorer mental health. That we found a relation of this sort with most categories of sensory disturbance is consistent with the findings of other investigations (2, 3). The association could have arisen, at least in part, because sensory symptoms cause psychologic distress. If this were the case, however, a stronger relation would have been expected for extensive than for limited median symptoms. Another possibility is that psychosocial influences predispose to the development, persistence, or awareness of some hand symptoms, as was indicated by a longitudinal study in which depression predicted the later occurrence of pain in the forearm (4). If so, the lack of association with extensive median symptoms would be consistent with their resulting from a distinct underlying pathology, median nerve compression at the wrist being the obvious candidate. We have previously observed that patients with hip osteoarthritis (which like carpal tunnel syndrome has a well-defined underlying pathology), although physically disabled, did not suffer from poorer mental health than did controls (5).
Different patterns of sensory symptoms in the hand also exhibited differential associations with physical activities (table 5). This analysis was based on a smaller sample size, being restricted to subjects who worked, and if some participants had left employment because of neck or upper limb disorders, then risks may have been underestimated. Furthermore, the assessment of exposure to activities was somewhat crude, and therefore the findings should not be taken to imply, for example, that prolonged use of a computer never causes upper limb disorders. Nevertheless, the distinctive associations with extensive median symptoms again point to a different disease process and, for the most part, would be compatible with underlying median nerve compression.
A causal role of physical activities in carpal tunnel syndrome, particularly forceful and repetitive movements of the wrist and hand, is widely accepted. For example, from a review of 15 cross-sectional studies and six case-control studies, Hagberg and Wegman (6) concluded that repetitive and forceful gripping was a major risk factor for occurrence of the syndrome, and when Silverstein et al. (7) classified the occupations of workers from seven different industries according to the degree of force and repetition required, they found that a combination of high force and high frequency carried an odds ratio of more than 15 for carpal tunnel syndrome in comparison with low force-low repetition jobs. Repeated movements of the elbow would not be expected to cause carpal tunnel syndrome, and the association that we found with extensive median symptoms may have resulted from confounding by other occupational activities.
Symptoms of numbness and tingling in the hands occur frequently in the general population (a point prevalence of 33 percent has been estimated in one British survey (8)), and several different symptom-based case definitions have been proposed previously to distinguish carpal tunnel syndrome from other patterns of complaint. Katz and Stirrat (9) defined symptoms as "classical" of carpal tunnel syndrome if they affected at least two of digits 13 but not the palm or dorsum of the hand, as "probable" if the palm was also involved, and as "possible" if symptoms were reported in only one of digits 13. Minor modifications to these criteria of Katz and Stirrat were later suggested by Franzblau et al. (10) and by Rempel et al. (11).
These proposals were framed on the basis of clinical consensus, rather than empirically by testing their association with expected clinical accompaniments of carpal tunnel syndrome. Subsequently, a classical distribution of symptoms as defined by Katz and Stirrat (9) was found to be sensitive and specific for delayed median nerve conduction in subjects with suspected carpal tunnel syndrome who had been referred for investigation in the hospital. However, the criteria did not predict delayed nerve conduction in community (8) or occupational (12) samples. A community survey by Ferry et al. (8) also explored the relation of delayed nerve conduction to various other symptom patterns, including hand symptoms that excluded the fifth digit, the dorsum, or both of these sites, but found the correlation to be similarly poor.
One possible explanation for these findings is that the criteria proposed were insufficiently specific in settings where the prevalence of median nerve compression was relatively low. Thus, in the definitions of "classical" and "probable" carpal tunnel syndrome according to the criteria of Katz and Stirrat (9), Franzblau et al. (10), and Rempel et al. (11), no attempt was made to exclude subjects who indicated symptoms in all of their digits; the criteria of Rempel et al. (11) do not seem to differentiate between palmar and dorsal involvement of digits 13; and in the survey by Ferry et al. (8), none among the several diagnostic categories defined required symptoms to be present in the palmar aspects of digits 13.
Our findings suggest that a further important determinant of specificity is the extent to which the palmar aspect of digits 13 is affected. Although Phalens and Tinels tests can by no means be regarded as accurate diagnostic markers for carpal tunnel syndrome, they do have limited diagnostic value, and it is notable that in hands with limited median symptoms these tests were positive less often than in those where numbness and tingling occurred in other anatomic distributions. Furthermore, the associations of limited median symptoms with psychosocial and physical risk factors did not resemble those for extensive median symptoms.
Our results suggest that, in classifying numbness and tingling in the hand, it may be useful to distinguish symptoms with an extensive median distribution from those with other anatomic patterns. A further test of this hypothesis would be to compare their correlations with nerve conduction measurements in a community setting.
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ACKNOWLEDGMENTS |
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The interviews and examinations were carried out by Trish Byng, Cathy Linaker, Claire Ryall, Karen Collins, and Angela Shipp. Ken Cox was responsible for the computer programming. The authors thank the doctors and staff of the two participating general practices.
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NOTES |
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REFERENCES |
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