Chronic hand vibration exposure is now a well-described cause of
Raynaud's phenomenon. According to Palmer et al, it is estimated that
220,000 cases of Raynaud's phenomenon are attributable to vibration
exposure in Great Britain.[1] These epidemiological data, based on a
questionnaire, are considered reasonably accurate.[2] About 4.2 million
workers are exposed to hand transmitted vibration but the real...
Chronic hand vibration exposure is now a well-described cause of
Raynaud's phenomenon. According to Palmer et al, it is estimated that
220,000 cases of Raynaud's phenomenon are attributable to vibration
exposure in Great Britain.[1] These epidemiological data, based on a
questionnaire, are considered reasonably accurate.[2] About 4.2 million
workers are exposed to hand transmitted vibration but the real health and
economic impact is unknown.[3] More precise clinical data are therefore
necessary before implementing a large preventive program.
The hand-arm vibration syndrome encompass a wide range of disorders being
responsible for digital blanching and paresthesias.[4] Different vascular
problems such as a pure vasospastic phenomenon, a digital organic
microangiopathy or an occlusive arterial thrombosis can be observed. A
diffuse vibration neuropathy with mechanical skin receptors involvement or
a carpal tunnel syndrome are also often associated.[5] The relationship
between these neurovascular disorders is not clear but autonomic
dysfunction in carpal tunnel syndrome can induce a Raynaud's phenomenon
which is curable with surgery.[6] The prognosis of these neurovascular
troubles is dependant on the underlying trouble and cannot be evaluated
with a simple questionnaire. As no single test can reliably stage the
vascular and neurological component, the use of a battery of tests is
necessary. Digital capillaroscopy and plethysmography with nerve
conduction studies are recommended as the basic tests. Cold provocation
tests are effective for grading a pure vasospastic Raynaud's phenomenon
but is less reliable in other forms of vibration-induced white finger
explaining why this test is not always well correlated with the vascular
symptoms.[7][8] Doppler and duplex studies are useful to assess the
severity of an occlusive arterial disease.
Workers using hand-held vibrating tools are also exposed to diverse
environmental and occupational factors accounting for the wide clinical
spectra of the disease. Epidemiological studies have pointed out that the
prevalence of vibration-induced white finger is very wide, ranging from 0-
5% in warm climate to 80-100% in northern climate.[9] In the pure
vasospastic Raynaud's phenomenon, cold exposure is probably the most
important triggering factor and cold protection the most effective
preventive measure. In the case of digital blanching associated with
carpal tunnel syndrome, other ergonomic factors such as repetitive
forceful use of the hands are likely to play a dominant role and a
workplace ergonomic modification is indicated.[10] Hypothenar hammer
syndrome is a another frequent cause of digital blanching in mechanics and
carpenters requiring prevention of repetitive hand trauma.[11][12] For the
digital organic microangiopathy and the diffuse vibration neuropathy,
vibration exposure is the only identified factor and suppression of the
exposition is essential. In consequences, a detailed and precise clinical
diagnosis with objective tests is important to determine the real cause of
the vascular symptoms. The impact of vibration exposure on health will be
more precisely evaluated and prevention will be more effective.
1. Palmer KT, Griffin MJ, Syddall H, et al. Prevalence of Raynaud's
phenomenon in Great Britain and its relation to hand transmitted
vibration: a national postal survey. Occup Environ Med 2000;57:448-52.
2. Palmer KT, Haward B, Griffin MJ, et al. Validity of self reported
occupational exposures to hand transmitted and whole body vibration. Occup
Environ Med 2000;57:237-41.
3. Palmer KT, Griffin MJ, Bendall H, et al. Prevalence and pattern of
occupational exposure to hand transmitted vibration in Great Britain:
findings from a national survey. Occup Environ Med 2000;57:218-28.
4. Noel B. Pathophysiology and classification of the vibration white
finger. Int Arch Occup Environ Health 2000;73:150-5.
5. Stromberg T, Dahlin LB, Rosen I, et al. Neurophysiological findings in
vibration-exposed male workers. J Hand Surg [Br] 1999;24:203-9.
6. Verghese J, Galanopoulou AS, Herskovitz S. Autonomic dysfunction in
idiopathic carpal tunnel syndrome. Muscle Nerve 2000;23:1209-13.
7. McLafferty RB, Edwards JM, Ferris BL, et al. Raynaud's syndrome in
workers who use vibrating pneumatic air knives. J Vasc Surg 1999;30:1-7.
8. McGeoch KL, Gilmour WH. Cross sectional study of a workforce exposed to
hand-arm vibration: with objective tests and the Stockholm workshop
scales. Occup Environ Med 2000;57:35-42.
9. Bovenzi M. Exposure-response relationship in the hand-arm vibration
syndrome: an overview of current epidemiology research. Int Arch Occup
Environ Health 1998;71:509-19.
10. Gemne G. Diagnostics of hand-arm system disorders in workers who use
vibrating tools. Occup Environ Med 1997;54:90-5.
11. Little JM, Ferguson DA. The incidence of the hypothenar hammer
syndrome. Arch Surg 1972;105:684-5.
12. Ferris BL, Taylor LM Jr, Oyama K, et al. Hypothenar hammer syndrome:
proposed etiology. J Vasc Surg 2000 Jan;31:104-13.
A meta-analysis that was recently published in this journal[1]
suggested an association between excess pancreatic cancer risk and
exposure to nickel and nickel compounds (meta-risk ratio = 1.9, 95% CI =
1.2 - 3.2, based on 4 studies). Through correspondence with the authors
(Ojaj rvi et al.), I learned that their analysis excluded the many
epidemiological studies that had been conducted on workers in the...
A meta-analysis that was recently published in this journal[1]
suggested an association between excess pancreatic cancer risk and
exposure to nickel and nickel compounds (meta-risk ratio = 1.9, 95% CI =
1.2 - 3.2, based on 4 studies). Through correspondence with the authors
(Ojaj rvi et al.), I learned that their analysis excluded the many
epidemiological studies that had been conducted on workers in the nickel
refining and alloy production industries. While most of these studies
could not contribute to the meta-analysis due to a failure to specifically
examine pancreatic cancer risk, I found two studies of nickel workers that
provide relevant data.
I believe that one of these studies, which examined mortality in
11,500 nickel mining and smelting workers,[2] should have been included in
the Ojaj rvi et al. meta-analysis,[1] based on the criteria used for study
selection. Another study of more than 30,000 workers exposed to nickel
and nickel compounds in the production of nickel alloys[3] was published a
few months after the May, 1998 cutoff that Ojaj rvi and coworkers utilized
to establish the data base for their meta-analysis. The results from
these studies[2][3] add substantially to data used in the Ojaj rvi et al.
analysis[1]:
Table 1 Cancer risks in studies
of workers exposed to nickel and its compounds
Study
Study Type
Included in Ojaj rvi et
al.[1] ?
Pancreatic Cancer Deaths
Relative Risk*
95% Confidence Interval
Thermoelectric
Plant Workers 4]
Cohort
Yes
1
3.6
0.1 -19.9
Cadmium/Nickel
Battery Workers[5]
Cohort
Yes
3
1.7
0.3 4.9
Los Angeles
workplaces[6]
Case-control
Yes
6
1.5
0.4 5.7
Montreal workplaces[7]
Case- Control
Yes
12
2.1
1.1 3.9
Nickel mining
and smelting workers[2]
Cohort
No
12
1.3
0.7 2.3
Nickel alloy
production workers[3]
Cohort
No
131
0.9
0.8 1.1
* SMR/100 for cohort studies.
Combining the data from all of these studies with the meta-analysis
random effects model employed by Ojaj rvi et al.[1] produces a meta-risk
ratio (MRR) of 1.3 (95% CI = 0.9 - 1.9). Interestingly, the two studies
designed specifically to detect excess cancer risks associated with
occupational nickel exposure[2][3] exhibit the lowest relative risks for
pancreatic cancer and differ substantially from the MRR for nickel
exposure calculated by Ojaj rvi et al. (1.9). Moreover, the estimated
relative risk (0.9) from the study of nickel alloy workers[3] is
significantly smaller (p<_0.05 than="than" even="even" the="the" lower="lower" _95="_95" confidence="confidence" limit="limit" for="for" ojaj="ojaj" rvi="ojaj rvi" et="et" al.1="al.1" mrr="mrr" _1.2.="_1.2." p="p"/> The fact that the Ojaj rvi et al.[1] MRR for nickel-related
pancreatic cancer significantly overestimates the risk observed in a large
cohort of nickel workers indicates that the authors' meta-analysis risk
estimates should be viewed with an appropriate degree of caution. These
meta-analysis results may be significantly biased because of limitations
of the studies on which they are based. In studies that relate to nickel,
the potential for misclassification bias is strong because of the complete
confounding of nickel exposure with known carcinogenic hazards such as
cadmium,[5] or asbestos, polycyclic aromatic hydrocarbons, chromium,
beryllium, polychlorinated biphenyls, and hydrazine.[4] Similarly, the
case-control study[7] that contributed the most substantial evidence of a
nickel-related pancreatic cancer risk to the Ojavarvi et al. meta-
analysis[1] provides equally strong statistical evidence of associations
between excess pancreatic cancer and exposures to ten other substances,
some of which are likely be correlated with occupational nickel exposure.
While Ojaj rvi and coworkers are to be congratulated on their
investigation of the aetiology of pancreatic cancer, it is my opinion that
their results are most appropriately viewed as hypotheses that require
further investigation, rather than compelling evidence that links
substances to the induction of pancreatic cancer. As Ojaj rvi et al.[1]
correctly suggest, research to test these hypotheses requires large
studies and more refined measures of exposure. With respect to nickel and
nickel compounds, data from large studies that were not included in the
Ojaj rvi et al. analysis[1] call into question the veracity of a
hypothesis that links nickel exposure to increased pancreatic cancer risk.
References
1 Ojaj rvi IA, Partanen TJ, Ahlbom A, et al. Occupational exposures
and pancreatic cancer: a meta-analysis. Occ Environ Med 2000;97:316-324.
2 Shannon HS, Walsh C, Jadon N, et al. Mortality of 11,500 nickel
workers - extended follow up and relationship to environmental conditions.
Toxicol Ind Health, 1988; 4:277-294.
3 Arena VC, Sussman NB, Redmond CK, et al. Using alternative
comparison populations to assess occupation-related mortality risk. J Occ
Env Med 2000;40:907-916.
4 Cammarano G, Crosignani P, Berrino H, et al. Additional follow-up
of cancer mortality among workers in a thermoelectric power plant. Scand
J Work Environ Health 1986;12:631-2.
5 Andersson K, Elinder CG, Hogstedt C, et al. Mortality among
cadmium and nickel-exposed workers in a Swedish battery factory. Curr Top
Environ Toxicol Chem. 1985;8:399-408.
6 Mack TM, Peters JM, Yu MC, et al. Pancreas cancer is unrelated
to the workplace in Los Angeles. Am J Ind Med 1985;7:253-256.
7 Siemiatycki J, Risk factors for cancer in the workplace, Boca
Raton, FL: CRC Press, 1991.
Dr Loomis draws attention to the potential dangers of the rigid use
of checklists and guidelines to judge occupational and environmental
research. I agree with these sentiments, in particular the concerns about
the increasing number of papers that use compliance with these guidelines
as a justification for conclusions regarding causality. There is, however,
one rapidly expanding area of research that...
Dr Loomis draws attention to the potential dangers of the rigid use
of checklists and guidelines to judge occupational and environmental
research. I agree with these sentiments, in particular the concerns about
the increasing number of papers that use compliance with these guidelines
as a justification for conclusions regarding causality. There is, however,
one rapidly expanding area of research that would benefit from the
development of minimum standards for presentation of results. This is the
field of epidemiological meta-analysis, in which data are generally
abstracted from published papers. Difficulties can arise in deriving a
common set of definitions for variables. For example, in a meta-analysis
of oral contraceptive use and breast cancer risk,[1] 42 different
categorisations of duration of oral contraceptive use were published in
the 24 papers analysed for this variable. Debate within the scientific
community is needed to decide categorisations that are most useful.
Editors could then encourage authors either to use these in their papers
or at least be prepared to make them available on request.
Reference
1. Rushton L, Jones DR. Oral contraceptive use and breast cancer
risk: a meta-analysis of variations with age at diagnosis, parity and
total duration of oral contraceptive use. Br J Obs Gyn 1992;99:239-246.
Editor,
Rushton's recent article on the reporting of occupational and environmental research raises a number of useful points that all researchers would do well to remember when writing up epidemiological findings for publication. Without expressly intending to do so, however, the article also emphasizes the hazards of establishing formal criteria or
checklists for the evaluation of scientific work. Good epi...
Editor,
Rushton's recent article on the reporting of occupational and environmental research raises a number of useful points that all researchers would do well to remember when writing up epidemiological findings for publication. Without expressly intending to do so, however, the article also emphasizes the hazards of establishing formal criteria or
checklists for the evaluation of scientific work. Good epidemiological practices certainly exist, but one of the pitfalls inherent in attempts to codify them is that, by their nature, lists of the features of "good"
research tend to impose a "one size fits all" standard, which - like clothing of the same description - fits nothing particularly well.
The prospect of developing formal guidelines for reporting analyses based on multivariable models illustrates the difficulties. Science involves many kinds of activities, but the significant advances come about through the creative application of human intellect, rather than by rote
repetition of the familiar. Like other aspects of science, epidemiological data analysis blends attention to factual detail with creativity, intuition, judgement and even aesthetics. From the initial choice of model
form to the final specification of covariates and interaction terms, there may be many reasonable ways to model a given data set. Researchers should
be at liberty to analyze their data according to their individual scientific insights. In subsequent evaluations of methods and results, reviewers likewise should be encouraged to apply their scientific judgement, rather than following a recipe.
The opportunity cost involved in demonstrating compliance with guidelines for good practice may also be considerable, as Rushton suggests. Between the growing fear of litigation and mounting demands for accountability, especially in the United States, epidemiologists may
soon spend more time documenting adherence to protocol than doing science.
My particular fear, however, is that guidelines will be used to assail sound research on the grounds that it fails to comply with supposed standards of good science. The misuse of Bradford Hill's ideas about causality illustrates the danger. Hill intended his suggestions as an aid
to researchers, not as evaluative standards for critics; he wrote: "I do not believe...that we can usefully lay down some hard-and-fact rules of evidence that must be obeyed before we accept cause and effect. None of my nine viewpoints ... can be required as a sine qua non. What they can do, with greater or less strength, is help us to make up our minds on the fundamental question." [1] Yet, Hill's ideas are frequently presented as criteria that must be fulfilled for a study's evidence to be accepted.[2]
The involvement of such obviously self-interested groups as the Chemical Manufacturers Association in promoting "good epidemiological practices" makes the potential misuse of guidelines to suppress good research seem all too likely.
I do not mean to suggest that all epidemiological research should be published or accepted at face value, far from it. There will always be a need for review to ensure the quality of published work and to protect the public from policies based on unsound science. I am convinced, however,
that peer review coupled with the opportunity for criticism and debate in the open literature provide the best pathway to this goal. In contrast with standardized criteria, these processes allow multiple, independent readers' perspectives concerning the methodological quality, and the substantive importance of research to be heard. As a result, they reduce
the chances that unconventional but valuable views will be suppressed or that an interested group could gain control over the process for their own purposes.
References
1. Hill AB. The environment and disease: association or causation? Proc R Soc Med 1965;58:295-300.
2. Gamble JF. PM2.5 and mortality in long-term prospective cohort studies: cause-effect or statistical association? Environ Health Perspect 1998;106:535-549.
Editor
Chronic hand vibration exposure is now a well-described cause of Raynaud's phenomenon. According to Palmer et al, it is estimated that 220,000 cases of Raynaud's phenomenon are attributable to vibration exposure in Great Britain.[1] These epidemiological data, based on a questionnaire, are considered reasonably accurate.[2] About 4.2 million workers are exposed to hand transmitted vibration but the real...
Editor
A meta-analysis that was recently published in this journal[1] suggested an association between excess pancreatic cancer risk and exposure to nickel and nickel compounds (meta-risk ratio = 1.9, 95% CI = 1.2 - 3.2, based on 4 studies). Through correspondence with the authors (Ojaj rvi et al.), I learned that their analysis excluded the many epidemiological studies that had been conducted on workers in the...
Dear Editor
Dr Loomis draws attention to the potential dangers of the rigid use of checklists and guidelines to judge occupational and environmental research. I agree with these sentiments, in particular the concerns about the increasing number of papers that use compliance with these guidelines as a justification for conclusions regarding causality. There is, however, one rapidly expanding area of research that...
Editor,
Rushton's recent article on the reporting of occupational and environmental research raises a number of useful points that all researchers would do well to remember when writing up epidemiological findings for publication. Without expressly intending to do so, however, the article also emphasizes the hazards of establishing formal criteria or checklists for the evaluation of scientific work. Good epi...
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