Prevalence of abnormal median nerve conduction in applicants for industrial jobs

There has been much debate regarding the work relatedness of carpal tunnel syndrome (CTS) and whether workers diagnosed with CTS had pre-existing disease at the time they were hired. To elucidate the latter issue, we examined the prevalence of abnormal median nerve conduction within the carpal tunnel in applicants for industrial jobs. Nerve conduction studies (NCS) were performed on both hands of 1,021 applicants following a conditional offer of employment. Each applicant completed a self-administered symptom survey specific to the upper extremity. Applicants had worked previously for an average of 4.4 (range 0–33) years and had a mean age of 30.1 (S.D. 8.9) years. Nerve conduction studies were performed in a private medical clinic. Sensory palmar latencies were determined over an 8 cm segment for the median and ulnar nerves. The difference between the median and ulnar sensory latencies was the primary electrophysiologic measurement used to determine median neuropathy. Using a very conservative criterion for abnormal median nerve conduction, 17.5% of the applicants were classified with neuropathy in at least one hand. Despite the relatively high prevalence of median neuropathy, relatively few (10%) with positive NCS acknowledged symptoms associated with CTS. Males had a higher percentage of median neuropathy than did females. We conclude that a large percentage of industrial workers have objective evidence of abnormal median nerve conduction within the carpal tunnel when hired. The high prevalence of abnormal median nerve conduction without corresponding symptoms may suggest a subclinical entity associated with CTS. © 1996 Wiley-Liss, Inc.     

Prevalence of musculoskeletal symptoms and carpal tunnel syndrome among dental hygienists

BACKGROUND: Carpal tunnel syndrome (CTS) and other work-related musculoskeletal disorders (MSDs) are common problems in general industry as well as dental hygiene. The purpose of this study is to determine the prevalence of CTS and other MSDs among dental hygienists. No previous studies involving dental hygienists have combined nerve conduction studies (NCS) and symptoms in their CTS case definitions. METHODS: Dental hygienists (N = 95) completed a symptom and job factors survey, hand symptom diagram, and underwent NCS across the wrist. RESULTS: At least one MSD was reported by 93%. Prevalence of CTS was 8.4% utilizing a case definition of symptoms and NCS, but 42% if defined by symptoms alone. Age, BMI, and the number of patients treated per day were significant factors associated with CTS. CONCLUSIONS: Dental hygienists are exposed to occupational factors that increase the risk of CTS. A case definition that does not include NCS overestimates CTS prevalence.     

Levels of agreement of nerve conduction studies and symptoms in workers at risk of carpal tunnel syndrome

Objective: Information is required on levels of agreement between different sets of median nerve conduction studies (NCS) and symptoms of carpal tunnel syndrome (CTS) in at-risk subjects. Methods: We performed a reanalysis of an extensive data set from a population of 114 highly exposed meat workers (without prior diagnosis of CTS), who were interviewed for the presence of current symptoms typical of CTS and systematically submitted to median NCS. Results: Agreement between presence/absence of symptoms and NCS normal/abnormal findings ranged from 81% for wrist sensory latency (WSL) to 49% for motor conduction velocity wrist-to-palm (MCV-WP) in the nondominant hands (from 60% to 50%, respectively, in the dominant hands). Mean values of WSL, sensory conduction velocity-WP (SCV-WP), wrist motor latency, MCV-WP, and the SCV-WP/SCV-elbow-to-wrist ratio all showed significant differences between symptomatic and asymptomatic workers. In nondominant hands, these parameters all reached significant P values at chi-squared tests for coefficients of agreement, the best coefficients being 0.57 for WSL and 0.40 for SCV-WP. However, in the dominant hand only SCV-WP reached significance ( coefficient=0.20). Conclusions: Given the importance of the dominant hand in working populations, these data support use of SCV-WP (or WSL) as an informative NCS parameter for occupational studies on CTS.     

Carpal tunnel syndrome among apprentice construction workers

BACKGROUND: In terms of lost-work time and restricted workdays, surgery, and rehabilitation, one of the most costly occupational musculoskeletal disorders is carpal tunnel syndrome (CTS). The purpose of this study was to determine the prevalence of CTS among apprentice construction workers. METHODS: This cross-sectional study included apprentices from four construction trades. Apprentices completed a self-administered questionnaire and received electrophysiologic studies assessing median nerve function across the carpal tunnel. A surveillance case definition for CTS was based on characteristic hand symptoms and the presence of median mononeuropathy across the carpal tunnel. RESULTS: Of the 1,325 eligible apprentices, 1,142 (86.2%) participated in the study. The prevalence of CTS among apprentices was 8.2%; sheet metal workers had the highest rate (9.2%). In operating engineers, the prevalence of CTS was significantly higher (OR = 6.9; 95% CI = 2.6-18.2) among the heavy equipment mechanics than the drivers of those vehicles. Body mass index, age, and self-reports of working overhead were associated with prevalent CTS. Less than 15% of the apprentices with CTS sought medical attention for their disorder. CONCLUSIONS: Many construction workers begin developing CTS before or during their apprenticeship. Few apprentices seek medical attention for hand symptoms characteristic of CTS. The results of this study indicate a public health need for the implementation of prevention strategies for CTS in the construction industry.     

Comparison of a digital electroneurometer and standard nerve conduction studies for the measurement of median nerve sensory latency

The purpose of this study was to determine the validity of measuring median nerve distal sensory latency with a portable digital electroneurometer. The results from the digital electroneurometer were compared to standard nerve conduction studies in 51 subjects (40 asymptomatic hands and 12 hands with probable carpal tunnel syndrome). There was a high correlation (r=0.92) between the latencies obtained from the electroneurometer and the onset latencies measured by standard nerve conduction studies. The mean difference between distal sensory latencies for matched pairs of latency measurements was 0.09 (+/–0.21) ms. The use of the digital electroneurometer for obtaining distal sensory latencies proved to be objective and valid. The electroneurometer would be useful in a variety of occupational and clinical settings for screening of peripheral neuropathy where standard nerve conduction equipment may be unavailable or impractical.     

Workplace surveillance for carpal tunnel syndrome using hand diagrams

Four hundred and eleven workers from 4 different companies participated in a worksite screening program designed, in part, to estimate the prevalence of carpal tunnel syndrome (CTS). Each worker completed a discomfort survey and underwent limited nerve conduction testing of the median and ulnar sensory nerves in both wrists. The discomfort survey included a hand diagram which allowed subjects to shade in area(s) affected by numbness, burning, tingling, or pain. The discomfort survey also asked each worker to indicate whether she or he had experienced neuropathic symptoms (i.e., numbness, burning, tingling, or pain) in the wrist, hand or fingers of each hand, without regard to localization (i.e., median versus ulnar versus radial distribution), and also nocturnal occurrence of symptoms. Analyses involved comparing hand diagram scores and non localized wrist/hand/finger symptoms with electrodiagnostic test results. All configurations of hand diagram scores of the dominant hands had a statistically significant association with electrophysiologically determined median nerve dysfunction, but so did non localized symptom reports. The sensitivity, specificity, and positive predicted values of hand diagrams were poorer than those reported previously. While some test performance characteristics of hand diagrams were better than those for non localized distal extremity symptoms consistent with CTS, some were worse. Overall, our data suggest that hand diagrams are no better than using a questionnaire to determine if workers have experienced symptoms consistent with CTS in their wrists, hands or fingers without regard to localization. The choice of screening tool would depend on the goal of screening, in particular, whether it is more desirable to have slightly higher sensitivity or positive predictive value.     

Subclinical impairment in the median nerve across the carpal tunnel among female VDT operators

Sensory nerve conduction velocities in the palm-to-finger (SCV-pf), wrist-to-finger (SCV-wf), wrist-to-palm (SCV-wp), and wrist-to-elbow (SCV-we) segments and the distribution of nerve conduction velocities in the right median nerve were determined among 27 female operators aged 19–37 and 19 healthy women (controls) aged 19-31 to estimate the prevalence of subclinical carpal tunnel syndrome (CTS). Also, the WF/PF ratio, dividing the SCV-wf by the SCV-pf, was calculated to assess abnormalities of nerve conduction within the carpal tunnel. The operators were engaged in data entry in front of a visual display terminal (VDT) for about 6 h/day, and their working duration was between 1 and 17 (mean 6) years. The SCV-wf, SCV-wp, and WF/PF ratio in the operators were significantly lower than those in the controls. The rate of persons with the WF/PF ratio of less than 90%, i.e., below normal limits in the 19 controls, was significantly higher in the operator group (37%) than in the control group (0%). The operators complained of more symptoms related to CTS than did the controls, but any symptoms were not associated with slowing of nerve conduction velocities in the operators. In the controls, the WF/PF ratio was not closely correlated with skin temperature or age despite the presence of significant relations between skin temperature and the SCV-wf, SCV-pf, and SCV-wp; the interpersonal variability of the WF/PF ratio was much smaller than that of all SCVs. In the light of the present and previous studies, the rate of VDT operators with subclinical CTS seems to be high, independent of its symptoms. Also, the WF/PF ratio will be a useful and reliable screening method for the early detection of CTS due to repetitive wrist and finger movements involved in work.     

Functional deficits in carpal tunnel syndrome

BACKGROUND: Carpal tunnel syndrome (CTS) is a major occupational illness in the US. The Wisconsin Test is a quantitative computer-controlled test battery designed for measuring sensory and psychomotor function. Subjects were recruited from industrial jobs at high-risk for CTS to determine if subtle sensory and motor deficits were observable in a working population. Outcomes were studied for potential use as an injury surveillance instrument. METHODS: A total of 208 subjects participated (72 males and 136 females). Participants completed a symptom survey, were given a physical examination, administered nerve conduction tests, and were tested using the Wisconsin Test battery. RESULTS: The greatest functional deficits were observed when nerve conduction findings were positive and were accompanied by either positive symptom survey outcomes or positive physical exam findings. The presence of symptoms alone were not significantly associated with motor deficits and no significant sensory threshold differences were observed among subjects categorized using any single criterion (i.e., nerve conduction, symptom reports, or examination). CONCLUSIONS: Measurable and quantifiable sensory and psychomotor deficits were observed in a working industrial population, and were greatest when positive symptoms or physical exam was accompanied by positive nerve conduction test findings. These data show that clinical criteria used in the diagnosis of CTS corresponds with functional psychomotor and sensory impairments measured in these tests.     

Comparison of outcomes of untreated carpal tunnel syndrome and asymptomatic controls in meat packers

Our objectives were to determine the reporting of symptoms, the medical outcome and the work status of meat plant workers diagnosed with clinical carpal tunnel syndrome (CTS). Forty-seven cases of CTS were identified from a previously reported study, and were matched by age, gender and hand use. Cases and controls were followed up for 24 months. The Provincial Workers' Compensation Board and company health records were used to determine the reporting of symptoms, interventions and work status. Thirty-one study cases and all control cases were followed for the full 24 months (16 study cases were lost to follow-up). In total, 12 cases reported symptoms of CTS during the 24 months (eight study cases and four controls). Of the eight study cases, one required surgical release of the carpal tunnel. After a period of work modification, five of the eight study cases returned to regular duty and the remainder were placed on permanent job restrictions. Of the four controls, one subject had a surgical release and returned to regular work, two subjects' jobs were permanently modified, and the fourth returned to regular duty. Occupation-related CTS in meat packers appears to be transient and responsive to conservative measures, with a surgical rate comparable to other occupations.     

Workplace surveillance for carpal tunnel syndrome: A comparison of methods

A variety of screening procedures for carpal tunnel syndrome (CTS) were applied among workers in a manufacturing plant, and results were compared. The test procedures included a symptom survey, physical examination, limited electrodiagnostic testing at the wrists, quantitative vibratory threshold testing, 2-point discrimination, palmar pinch grip, and hand grip strength testing. When electrodiagnostic testing alone was used as gold standard, the sensitivity and positive predictive value (PPV) of physical examination findings and quantitative test procedures were no better than, and usually worse than, the results on the symptom survey alone. Variation of the constellation of symptoms (i.e., numbness, tingling, pain or burning) and the anatomic distribution of reported symptoms (i.e., fingers, hand, wrist, or forearm) for inclusion in the screening symptom definition of CTS yielded modest changes in the sensitivity and PPV of the symptom survey. However, addition of the requirement for nocturnal symptoms as part of the screening symptom definition for CTS resulted in substantially higher PPV with only slight reduction in sensitivity. These results suggest that, in the absence of electrodiagnostic testing, the simplest test, and the procedure with the highest sensitivity and PPV for CTS is a symptom survey alone. Quantitative test procedures (vibrometry, pinch grip strength, hand grip strength) and physical examination for findings consistent with CTS (e.g., Phalen's test, Tinel's test, thenar muscle wasting, 2-point discrimination) appear to contribute little, if any, additional information when screening subjects in the work setting.     

A cross-sectional study of musculoskeletal symptoms and risk factors in semiconductor workers

As part of the cross-sectional component of the Semiconductor Health Study, we assessed prevalence of specific musculoskeletal symptoms and their association with possible ergonomic risk factors. A total of 3,175 persons (78% participation rate) from eight manufacturing sites across the U.S. completed a health and work questionnaire. Using logistic regression methods to adjust for nonoccupational factors, we compared musculoskeletal symptom (self report) prevalence among fabrication room (fab) and nonfab workers, among specific work process groups, and among workers exposed to selected ergonomic stressors. Overall, seven of 12 musculoskeletal outcomes were significantly more prevalent among fab workers. Distal upper-extremity symptoms were more common among fab than nonfab workers [relative risk (RR) = 1.44, 95% confidence interval (CI) = 1.26-1.63] and showed a dose-response effect with hours per day spent in the fab; increased risk was associated with frequency of lifting and with use of vacuum wands and projection aligners. female sex and high somatization index score were associated with increased reporting for all musculoskeletal outcomes.     

Clinical and employment outcomes of carpal tunnel syndrome in oregon workers’ compensation recipients

We examined demographic, occupational, and treatment characteristics in 316 Oregon workers with carpal tunnel syndrome (CTS) to identify factors associated with clinical and employment outcomes. The goal of this hypothesis-generating study was to identify factors amenable to change through return-to-work programs. Mean claim duration numbered 217 days; median duration was 194 days. Sixty-one percent of workers received timeloss pay at some point during their claim. Workers having CTS surgery numbered 196 (62%). Variables predicting greater days of timeloss in workers with surgery (n=192) included: (1) decreased ability to “get along on income,” (2) attorney involvement, (3) fewer years education, (4) having bilateral surgery, (5) having physical therapy before surgery, (6) longer claim duration, and (7) hand-intensive occupational tasks (r²=36%, adjusted r²=34%). The interplay between occupational and non-occupational factors mandates a comprehensive approach to the evaluation and treatment of workers with CTS.     

Use of ultrasonography in monitoring work-related carpal tunnel syndrome: A case report

Carpal tunnel syndrome (CTS) is a syndrome whose diagnosis is well established. One cause could be occupational factors, while others have no relation to work or the work environment. We present in this article a case report regarding a worker affected by CTS, which is of interest concerning the sensitivity of ultrasonography and electroneurography, applied as diagnostic methods, related in our protocol to the variations in occupational exposures. The case reports an agricultural worker, whose tasks required repetitive and high frequency movements of the hand-arm. Diagnosis of CTS used ultrasonography and electroneurography techniques. In our opinion, the clinical evolution of CTS encompasses three “work-related” phases (preclinical phase; phase of nerve compression; phase of irreversible damage). Ultrasonography provides greater information about the evolution of CTS, as well as other cumulative trauma disorders, and is able to discern tendinitis of flexors causing a compression on the median nerve in the carpal tunnel. Am. J. Ind. Med. 33:560–564, 1998. © 1998 Wiley-Liss, Inc.     

Sensory nerve conduction velocities of median,ulnar and radial nerves in patients with vibration syndrome

OBJECTIVE: The present study aimed to clarify the range of involvement for hand-arm vibration syndrome (VS) in the median, ulnar and radial nerves of the hand. METHODS: Sensory nerve conduction velocities (SCVs) for 3 nerves in the hands and arms were examined for 34 patients with VS and 23 age-matched controls. Neuropathy types were classified by possible carpal tunnel syndrome (CTS), Guyon's syndrome and digital neuropathy in three nerves. RESULTS: SCV in the median nerve (middle finger, wrist-elbow) and ulnar nerve (little finger, wrist-elbow), and amplitudes of the median nerve (wrist-proximal and distal parts of the middle finger), ulnar nerve (wrist-proximal and distal parts of the little finger; forearm-proximal part of the little finger; upper arm-proximal part of the little finger) and radial nerve (dorsal side of the hand-thumb) were significantly reduced in VS patients compared with controls. According to subject classifications based on the results of SCV and amplitude of nerve action potential, 52.9% of VS patients displayed multi-focal neuropathy including digital neuropathy, possible CTS and/or Guyon's syndrome. CONCLUSION: These findings suggest that VS affects all three nerves in the hand. According to classification results, the main disorders of peripheral nerves comprise digital neuropathy.     

Syndromes from segmental vibration and nerve entrapment: observations on case definitions for carpal tunnel syndrome

Objectives The purpose of this paper is to assess the overlap and stability of two different case definitions of carpal tunnel syndrome CTS. The analysis considers the association between different case definitions and objective tests (sensory nerve conduction velocities, SNCVs and vibrotactile perception thresholds, TTS), and the natural history of CTS, in the context of two vibration-exposed cohorts. Methods Clinical CTS cases were defined in two ways: (1) by the study physician using fixed criteria, and; (2) by questionnaire and hand diagram. SNCV in median and ulnar nerves was measured for digital, transpalmar, and transcarpal segments, and conventionally as from wrist-digit. Skin temperature was assessed as a point measurement by thermistor and regionally by thermal imaging. VTTs were determined at the bilateral fingertips of the third and fifth digits using a tactometer meeting the requirements of ISO 13091-1 (ISO 2001). The subjects were cohorts of shipyard workers in 2001 and 2004, and dental hygienists in 2002 and 2004. Results Results are reported for 214 shipyard workers in 2001 and 135 in 2004, and for 94 dental hygienists in 2002 and 66 in 2004. In 2001, 50% of shipyard workers were diagnosed as CTS cases by at least one of the diagnostic schemes, but only 20% were positive by both criteria. Among study physician diagnosed cases, 64% were CTS negative in 2001, 76% were negative in 2004, 13% were positive in both years, 22% became negative after being positive, and 11% became positive after being negative. For only study physician diagnosed CTS did VTTs differ between cases differ and non-cases in digit 3; there was no such distinction in digit 5. The dental hygienists had little CTS. Conclusion Clinical case definitions of CTS based on diagrams and self-assessment, and clinical evaluation have limited overlap. Combining clinical criteria to create a more narrow or specific case definition of CTS does not appear to predict SNCV. The natural history of CTS suggests a protean disorder with considerable flux in case status over time.     

Clinical determination of work-relatedness in carpal tunnel syndrome

The purpose of this study was to determine the diagnosis and work-relatedness of carpal tunnel syndrome (CTS) using standardized criteria in a series of cases that were referred for an independent medical examination with a prior diagnosis of work-related CTS. using a liberal case definition, only 65% of cases had CTS. Using Wisconsin's worker's compensation criteria for work-relatedness, only 55% of the cases had any work-related disorder, while only 37% of the cases had work-related CTS. Duration of exposure was not significantly associated with work-related vs. non-work-related CTS. It was noted that the development of non-work-related CTS cases occurred uniformly across the various durations of exposure, as if unrelated to exposure. The symmetry of the disorder was unrelated to work-relatedness, provided that the symmetry of the disease matched the symmetry of the exposure. Personal characteristics, such as obesity and diabetes, revealed no statistically significant associations with work-relatedness or CTS. The present findings illustrate application of a standard procedure for determining the work-relatedness of CTS in a series of cases referred for independent medical examination. The results indicate that CTS is often, overdiagnosed and inaccurately linked to work. While the results may be limited by the method of determining work-relatedness, the findings indicate the importance of careful consideration of criteria for CTS and work-relatedness. When such an approach is taken, more targeted clinical management of the patient and appropriate intervention in the workplace should result.