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Occupational Medicine Advance Access originally published online on April 3, 2008
Occupational Medicine 2008 58(3):181-186; doi:10.1093/occmed/kqn027
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© The Author 2008. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

The sensitivity and specificity of thermometry and plethysmography in the assessment of hand–arm vibration syndrome

Aaron Thompson, Ron House and Michael Manno

Department of Occupational and Environmental Health, St Michael's Hospital, 30 Bond Street, 4th Floor Shuter Wing, Toronto, Ontario M5B 1W8, Canada

Correspondence to: Aaron Thompson, Occupational and Environmental Medicine Clinic, St Michael's Hospital, 30 Bond Street, 4th Floor Shuter Wing, Toronto, Ontario M5B 1W8, Canada. Tel: +1 416 864 5074; fax: +1 416 864 5421; e-mail: aaron.thompson{at}utoronto.ca


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
 References
 
Background Finger plethysmography and thermometry are objective measures used to assess the vascular aspect of hand–arm vibration syndrome (HAVS). Research to date shows poor correlation between these tests and Stockholm Workshop Scale (SWS) vascular stage. Clinicians, researchers and compensation boards require objective means to diagnose and quantify HAVS.

Aims To define the specificity and sensitivity of thermometry and plethysmography using the SWS as the reference criterion. A secondary goal was to consider cut points for the tests optimizing sensitivity and specificity.

Methods A cross-sectional analysis was conducted on HAVS patients seen at an occupational medicine specialty clinic. Plethysmography and thermometry were analyzed using SWS vascular stage as the outcome variable. Logistic regression controlled for age, smoking and time since last vibration exposure and use of vasoactive medications. The sensitivity and specificity of the combined tests were calculated using varying cut points.

Results A total of 139 patients consented to participate in the study. Plethysmography stage 1 or greater showed the highest sensitivity (sensitivity 94% and specificity 15%). Specificity was optimized combining plethysmography stage 3 and thermometry stage 3 (specificity 98% and sensitivity 23%). Maximal diagnostic accuracy was achieved by plethysmography alone setting the criteria for a positive test as being stage 1 or greater (70%).

Conclusions Neither plethysmography nor thermometry either alone or in combination demonstrated sufficient sensitivity and specificity to serve as an objective correlate for SWS vascular stage. All combinations of plethysmography and thermometry showed a lower specificity than sensitivity indicating that the SWS may be less sensitive in detecting vascular pathology than the objective tests.

Keywords      Hand–arm vibration syndrome; occupational; photocell plethysmography; sensitivity and specificity; Stockholm Workshop Scale; thermometry


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Conflicts of interest
 References
 
Hand–arm vibration syndrome (HAVS) is a recognized occupational disorder characterized by circulatory disturbances, sensorineural disruption and damage to the muscles, bones and joints [1,2]. The Stockholm Workshop Scale (SWS) constitutes a classification scheme for the vascular aspect of HAVS based on a patient's subjective history [3], while cold provocation testing using finger skin temperature recovery and plethysmography provide objective measures of vascular pathology. Studies to date have found the objective vascular tests to correlate poorly with symptoms as measured by the SWS [4–10]. Criteria for a positive test can be selected to maximize either sensitivity for screening purposes or specificity for diagnostic purposes. The literature does not demonstrate any studies examining varying cut points to define a positive test to maximize test performance (sensitivity or specificity).

Finger skin temperature is a physiologic parameter used to evaluate cold-induced vasoconstriction in the digital vessels. A delay in rewarming signifies persistent digital vasospasm [7,11]. Using the SWS as the reference, cold provocation finger thermometry has been shown to have a sensitivity between 49 and 73% and a specificity between 43 and 92% [7,12–16]. The wide range may reflect the fact that finger skin temperature is a complex response that is not easily reduced to a single measure, varying methodology between studies including differences in water temperature, time of immersion and time of measurement and poor suitability of the chosen reference standard [17].

Cold provocation photocell plethysmography has been described in the literature [14,18,19]. Interpretation of the tracings from photocell plethysmography uses pulse amplitude as an indicator of vasospasm [11] and tracing shape as a marker of vascular abnormality [20]. Laroche and Theriault [14] compared the results of digital plethysmography with clinical evaluation and found a sensitivity of 70% and specificity of 37%, while Olsen [17] compared cold provocation finger systolic blood pressure tests with visual inspection and found a sensitivity of 96% and specificity of 64%. Similar to thermometry, this wide range may reflect differences in testing technique, apparatus or choice of reference criterion.

This study aimed to determine the sensitivity and specificity of the objective vascular tests using a cross-sectional design and SWS vascular stage as the outcome variable. By defining varying cut points, the sensitivity and specificity of the objective tests may be optimized depending on whether they are to be used for screening or diagnostic purposes.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Conflicts of interest
 References
 
The study population consisted of consecutive patients investigated for HAVS at St Michael's Hospital, Toronto, Ontario, Canada. The collection of the data used in the study was approved by the Ethics Review Committee of St Michael's Hospital, a tertiary care hospital affiliated with the University of Toronto. Patient assessment consisted of a questionnaire, history and physical exam, laboratory studies to rule out secondary causes of Raynaud's phenomenon and cold provocation tests using plethysmography and thermometry. Smoking and use of caffeine were not restricted prior to testing, although vascular testing was conducted after the worker had been in the clinic for at least 1 h, during which time coffee was not consumed and smoking was not allowed. Smoking status and time since last vibration exposure were recorded. One of two occupational medicine physicians conducted the examinations using the same standardized protocol. After the history and physical exam, the physician assigned the patient a SWS vascular stage based on the patient's symptoms. For each patient, the clinical assessment was conducted on the same day as the objective tests to eliminate variation in underlying vascular effects at the time of reporting symptoms and conducting the tests. Thermometry and plethysmography were performed at two sites that were blinded to each other and to the SWS results.

The study used a standardized protocol and apparatus for both thermometry and plethysmography. The protocols for both tests have been previously described [10,21,22]. Baseline measurements were recorded at an ambient room temperature between 21 and 24°C for both testing modalities. Plethysmography involved the immersion of the hands in 10°C water for 2 min. Post-immersion results were then compared to baseline measurements. The tracings were interpreted on a scale of 0–3 with 0 signifying no abnormality pre- and post-cold and 1–3 signifying mild, moderate and severe disease, respectively.

Finger skin temperature was measured using thermocouplers attached to the tip of each digit. Baseline values were obtained over a period of 2 min prior to immersion. The hands were then immersed in 10°C water. A sphygmomanometer was inflated around each of the patient's wrists for the initial 5 min of immersion. The sphygmomanometer was then deflated and the hands were kept immersed for a further 2 min. The skin temperature of the digits was recorded throughout the 7-min immersion period and for a further 7 min following immersion. The parameters described by Pelmear et al. were used to assess rewarming [21,22]. Cold-induced vasospasm was diagnosed when a prolonged recovery phase was recorded and was graded as being 0 (no abnormality) or 1 (mild), 2 (moderate) or 3 (severe).

SWS vascular stage was used as the outcome variable based on dichotomization of SWS into stage 0 or 1 versus stages 2, 3 or 4 (no disease/mild disease versus more severe disease). Two by two tables were constructed to determine the sensitivities and specificities for the tests either singly or combined using varying cut points to define a positive result.

Statistical analyses were performed using SAS, version 8.0 (SAS Institute Inc., Cary, NC, USA).


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Conflicts of interest
 References
 
The demographic parameters of the 139 study subjects are outlined in Table 1. Participants were primarily from the mining, construction and automotive trades. The majority of participants were male and between 40 and 60 years of age (61%). Twenty-one (15%) were >60 years old while 33 (24%) were <40 years old. The mean length of vibration exposure was 23.9 years (SD = 11.3, range 0.5–47). Forty-eight participants were smokers (35%) and 38 (27%) were using vasoactive medication.


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  		Table 1. Characteristics of study population

 
Table 2 displays the distribution of SWS vascular stage in the study population. Sixty-three (45%) of the participants were SWS vascular stage 3, 34 (25%) were stage 2, 22 (16%) were stage 1 and 19 (14%) were stage 0. One subject was classified as stage 4 due to trophic changes in the fingers. The dominant hand was chosen for purposes of analysis.


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  		Table 2. Vascular stage in study population

 
Table 3 displays the results of two by two tables constructed to determine the sensitivities and specificities for the objective tests alone and in combined. Sensitivity was maximized when a positive test was defined as the presence of disease demonstrated by either plethysmography or thermometry (84 or 87%). Specificity was maximized if a positive test required both thermometry and plethysmography to be positive (45 and 44%). In all cases, sensitivity was higher than specificity, indicating the presence of a high number of false positives. In this context, false positives were recorded if the objective test noted presence of disease while the SWS did not record any symptoms.


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  		Table 3. Test parameters using the SWS as the reference measure

 
Test parameters using varying criteria for thermometry are shown in Table 4. When the criterion for a positive test was severity 1 or greater, the sensitivity was 88% and the specificity 24%. This criterion also showed maximal diagnostic accuracy (the proportion of correct classifications), which was 69%. In other words, the test results and SWS diagnosis agreed 69% of the time.


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  		Table 4. Sensitivity and specificity of thermometry versus Stockholm vascular stage (dominant hand)

 
Test parameters using varying criteria for plethysmography are shown in Table 5. When the criterion for a positive test was tracing dampening >1, the sensitivity of the test was 94% and the specificity 15%. Maximal diagnostic accuracy (70%) was also achieved when this criterion was used.


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  		Table 5. Sensitivity and specificity of plethysmography versus Stockholm vascular scale (dominant hand)

 
Table 6 shows the results of the combined tests using varying cut points. Maximum sensitivity was seen when the criterion for a positive test was stage 1 severity or greater for both tests (sensitivity 87% and specificity 27%), while specificity was maximized when parameters for a positive test required both tests to be stage 3 severity (sensitivity 23%, specificity 98%). Maximal diagnostic accuracy was achieved when the criterion for a positive test was set as plethysmography stage 1 or greater and thermometry stage 1 or greater and was 69%.


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  		Table 6. Sensitivity and specificity combined tests using varying criteria for a positive test (dominant hand)

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Conflicts of interest
 References
 
The principal finding of this study was that neither plethysmography nor thermometry, either alone or in combination using varying cut points, demonstrated sufficient sensitivity and specificity to be used as objective tests for SWS vascular stage. This is consistent with the literature, which suggests that both plethysmography and thermometry have poor predictive value when the SWS is used as the reference standard [4–10]. Combining the tests using varying cut points added little value to improve overall diagnostic accuracy. Plethysmography provided the highest sensitivity (94% using criteria stage 1 or greater), while combining the tests and requiring both to be stage 3 achieved the highest specificity (98%).

Methodological strengths of this study included attention to blinding of the measurements being compared, carrying out the clinical evaluation and objective tests on the same day to eliminate temporal variation and a relatively large sample size. This study was unique in its considering the ability of the objective tests to discriminate between no disease/mild disease and more severe stages of the disease, as previous studies have only considered the sensitivity and specificity of the tests comparing cases to controls. A limitation of this study was that no unexposed control group was available for comparison, although 19 participants were in stage 0 of the SWS. A second limitation is that the generalizability of results may be limited given that the study population was predominantly male. An additional limitation was that no restrictions on smoking or caffeine use were placed on subjects prior to testing; however; it should be noted that the vascular tests were not started until the worker had been in the clinic for at least 1 h during which time coffee was not consumed and smoking was not allowed. Additionally, smoking status, age, use of vasoactive medications and time since last vibration exposure were not found to significantly correlate with SWS vascular stage in a prior analysis of these data [10].

The low sensitivities of the objective tests may be due to the SWS being less sensitive than the objective tests in indicating mild pathophysiologic changes. This conclusion is supported by the literature, which reveals that plethysmography and thermometry may detect preclinical pathological vasospastic disease [12,17,23,24]. The results of this study are consistent with this because plethysmography and thermometry consistently showed specificity to be lower than sensitivity (Table 3). This indicates that when the SWS is used as the reference criterion, there were a higher number of false positives than false negatives. False positives may result from either poor validity of a test or low sensitivity in the reference standard to the underlying vascular abnormality. The validity of the objective tests is supported by the fact that the results of plethysmography correlate reasonably well with thermometry [10]. As such, it would seem that the ‘false positives’ being detected are the result of the objective tests detecting early vasospastic disease in asymptomatic patients [17].

The low specificities of the objective tests in this study indicate that some subjects report clinical manifestations of vascular symptoms in the absence of positive findings on objective testing. Recall or reporting bias is possible given that in HAVS, like in many clinical scenarios, physiologic changes are not proportional to subjective symptomatology. Additionally, neurological and vascular symptom severity do not always correlate, so individuals with severe neurological symptoms may over report vascular symptoms. Ambiguity of terms (occasional, frequent and most) and mixing of symptom frequency with extent of blanching in the SWS may contribute to misclassification bias [19,25]. The SWS is also subject to misclassification bias due to its assumption that blanching score and frequency of attacks increase together, an assumption that has been shown to be incorrect [26].

Compensation decisions are usually based upon clinical manifestations of occupational disease, and verification of symptoms by objective tests is often required in order to process claims. Cold water provocation thermometry and plethysmography are helpful in detecting pathophysiologic changes in HAVS patients [10]. The problem with using the objective tests to confirm the diagnosis of clinically apparent HAVS is that they may detect preclinical disease and result in false positives. Objective verification of the presence of HAVS may be better achieved by selecting criteria for a positive test that optimizes specificity. However, higher specificity is usually associated with lower sensitivity and consequently some valid claims would be rejected.

Future research on objective testing for the vascular effect of HAVS should focus on two areas. The reference criterion used to measure the performance of traditional tests such as plethysmography and thermometry needs to be re-evaluated. A different reference criterion such as direct clinical observation or use of pictures of patient's hands during episodes of typical blanching may help to eliminate recall bias. Alternatively, an approach such as cluster analysis might help to determine which patients are similar in terms of combinations of symptoms and test results. A second area of future research should be to focus on alternative methods of objective testing such as cold provocation tests using laser Doppler or MR angiography [27].


Key points
  • Neither plethysmography nor thermometry, alone or in combination using varying cut points, demonstrated sufficient sensitivity and specificity for them to serve as objective tests for SWS vascular stage.
  • Objective verification of HAVS is best achieved by selecting criteria for a positive test that optimize specificity, although this may lead to an unacceptable number of false negatives.
  • The objective tests may be more sensitive in detecting vascular abnormalities than the SWS, making the SWS poorly suited for use as the reference standard for determination of diagnostic accuracy.

 


   Conflicts of interest
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
References
 
None declared.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
 References
 

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