Academic journal article Scandinavian Journal of Work, Environment & Health

A Prospective Cohort Study Investigating an Exposure-Response Relationship among Vibration-Exposed Male Workers with Numbness of the Hands

Academic journal article Scandinavian Journal of Work, Environment & Health

A Prospective Cohort Study Investigating an Exposure-Response Relationship among Vibration-Exposed Male Workers with Numbness of the Hands

Article excerpt

Hand-arm vibration syndrome (HAVS), caused by hand- arm vibration (HAV), comprises both vascular and sensorineural symptoms with occurrence and progress seemingly independent of each other (1). Cases of HAVS have been reported mainly in countries with colder climates but also in tropical regions (2). The most evident sensorineural symptoms are tingling and numbness of the hand, and it has been tentatively sug- gested that the earliest symptoms are more likely to be neurological, preceding vascular symptoms (3).

Evidence for an exposure-response relationship for HAV exposure and neurological (sensorineural) symptoms is not very strong (3, 4). There are few lon- gitudinal studies investigating this relationship and most of the reported studies have been cross-sectional (5-7). Establishing an exposure-response relationship would increase knowledge on vibration exposure and may help to avoid or minimize adverse health effects from HAV and quantify the risk for a certain exposure level.

The aim of this study was therefore to investigate the exposure-response relationship of HAV exposure to neurological symptoms (numbness) of the hand in a cohort of vibration-exposed workers. The majority of those with HAVS are considered to suffer from neurological symptoms, and the main interest in this study is for the neurological component of HAVS as the vascular disorder has been more extensively inves- tigated (3, 8).

Methods

Cohort

The cohort consisted of male manual and office work- ers at an engineering plant in Sweden (9). Staggered start dates were used for the recruitment constituting the baseline: 1st recruitment=1 January 1987, 2nd=31 January 1992. Of a total of 500 office workers, 61 were randomly invited from the employee roster to participate in the study. Those accepting participation, along with all employed 112 manual workers, comprised the cohort of 151 subjects in 1987. In 1992 additional subjects were invited to participate, resulting in 241 subjects in total, of whom 60 were unexposed and 181 exposed (table 1). Occupations among the manual workers included mainly welders, tool grinders, turners and steel platers. Occupations among office workers included salespeople, managers, engineers, secretaries, and financial clerks. Exclusion criteria were age ≥55 years (1987) and use of drugs with the potential to affect the nerve system and result in neurological symptoms.

Follow-ups were performed in 1992 (for those recruited in 1987) and 1997, 2002, and 2008. The cohort consisted of 241 subjects in 1992, and there were 220, 195, and 197 subjects, respectively, at the follow-ups in 1997, 2002, and 2008.

Table 1 presents the study population for the differ- ent years of recruitment and follow-ups, including the number of exposed and unexposed subjects, subjects lost to follow-up, and returning subjects (10).

Data collection on symptoms and exposure

Symptoms. An experienced physician performed a standardized medical examination and interview focus- ing on neuromuscular symptoms and signs of the hand and upper extremity in 1987 (N=151), 1992 (N=241), 1997 and 2008. In 2002, there was no medical exami- nation and data was collected via a questionnaire. During each follow-up, a questionnaire on symptoms of the hands was used. Numbness was defined as loss of sensation in the hands and/or fingers and was con- sidered present if the subject answered positively to the screening question on suffering from numbness in the hand or fingers. The question on numbness was linked to a question on debut year. In this way it was possible to reach subjects who had missed out on a follow-up and then returned to the study. Where reported debut year differed on the various follow-up occasions, we selected the earliest year or the year that was reported most frequently as the year of debut. Subjects were also asked to report current or previous diagnosis of carpal tunnel syndrome (CTS), hand or arm trauma, and whether they considered the reported numbness to affect their work performance. …

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