Abstract
The severity of hand–arm vibration syndrome (HAVS) is usually graded according to the Stockholm workshop scales. Although the Stockholm workshop scales are regarded the gold standard for assessing the severity of HAVS, they are based primarily on subjective symptoms. The aim of the present study was to explore the agreement between Stockholm workshop scales and the outcome from ten well-defined clinical tests commonly used in hand rehabilitation for assessment of hand function. One hundred and eleven vibration-exposed workers participated in the study. Ten objective tests of hand function and four questions on subjective hand symptoms were included. The results indicated that, out of these tests, perception of vibration, perception of touch/pressure and dexterity showed a moderate agreement with Stockholm workshop scales. Among specific questions on hand symptoms, cold intolerance and pain showed a high agreement with Stockholm workshop scales. It is concluded that defined objective tests combined with directed questions on specific hand symptoms, together with the Stockholm workshop scales, may be helpful for diagnosing HAVS.
INTRODUCTION
The hand–arm vibration syndrome (HAVS) is a complex condition associated with vibration exposure and the use of hand-held vibrating machines. White fingers (Agate, 1949), sensory disturbances and reduced dexterity (Brammer et al., 1987; Lundborg et al., 1992) are well-known presentations. In addition, usually in more severe cases of the disease (Bilgi and Pelmear, 1993), vibration-exposed workers have reduced hand grip strength, despite well preserved muscle bulk (Färkkilä et al., 1986). Earlier research has identified three distinct symptom groups with sensory disturbances, white fingers, or a combination of these two symptoms dominating (Strömberg et al., 1996). Other hand symptoms that can be present in HAVS are cold intolerance, pain and muscle cramps (Fridén, 2001; Strömberg et al., 1996; Yamada et al., 1994).
Due to the complexity of the disease, the difficulty in diagnosing HAVS is well known (Noël, 2000; Pelmear and Kusiak, 1994). The HAVS diagnosis is usually based on a history of vibration exposure and the presence of symptoms, and it can be supported by a number of laboratory tests. In the UK, “HAVS is considered to exist if, after prolonged exposure to hand-transmitted vibration, involvement of the vascular and/or peripheral nervous system occurs, with or without musculoskeletal involvement” (HSE, 1994). The Stockholm workshop scales are classifications for the sensorineural (neurological) (Brammer et al., 1987) and vasospastic (vascular) (Gemne et al., 1987) symptoms in vibration injury (Tables 1 and 2). The scales measure subjectively perceived symptom severity as interpreted by a physician. The scales are well accepted and are widely used in clinical situations (Bilgi and Pelmear, 1993; Chetter et al., 1998; Gemne et al., 1993). In fact many clinicians and researchers consider them to be the gold standard in diagnosing HAVS. However, several authors have argued that the Stockholm workshop scales being based mainly on subjective symptoms, have limitations and that objective clinical tests would be valuable and helpful. For instance, McGeoch et al. (1994) discovered that multiple sensory tests increased the accuracy of the Stockholm workshop staging and that aesthesiometry, temperature neutral zone tests and grip strength were helpful when separating sensorineural stages 0 and 1 from stages 2 and 3. Furthermore, Kent et al. (1998) found that an acceptable level of accuracy in the Stockholm workshop scales was possible with a combination of tests such as plethysmography, vibrometry, two-point discrimination and Semmes–Weinstein monofilament testing. Regarding the vascular component, Matoba et al. (1995) reported that cold sensations appear long before the occurrence of white fingers. Other authors have also studied different combinations of tests in order to improve the Stockholm workshop staging (Gemne, 1997; Haines and Chong, 1987; Ishitake et al., 1995; Lawson and McGeoch, 1999; Lawson and Nevell, 1997; Matoba et al., 1995; McGeoch and Gilmour, 2000; Pelmear and Kusiak, 1994; Strömberg et al., 1998) but no consensus has yet been reached as to which tests best improve the Stockholm workshop staging.
Clinical outcomes, either subjective or objective, can be judged with subjective as well as objective measures. A subjective outcome is when the observation is concerned with the subjective state of a person while an objective outcome is independent of subjective perceptions. A subjective measure is influenced by different sources of variation, and thus its reliability is unknown or lacking (Jette, 1989). A good objective measure should be standardized and tested for validity and reliability and there should be instructions for administrating the test, a description on the equipment used, normative data, and a bibliography (Fess, 1995). Calculating sensitivity and specificity is one way of estimating the validity of a test when comparing it to a gold standard, while exploration of relationships between data generated from different assessment instruments (tests, questions) yields information on whether the different instruments measure the same or different aspects of a disease.
With regard to the diagnosis of HAVS, the value of using a number of objective tests of hand function or asking questions regarding subjective hand symptoms not included in the Stockholm workshop scales is largely unknown. In order to assess this, it is necessary to explore the agreement between the Stockholm workshop scales and other outcome instruments currently used by hand rehabilitation departments. The aim of this study was to investigate the sensitivity and specificity of ten objective tests of hand function and four questions on subjective hand symptoms for the detection of neurological and vascular HAVS, as diagnosed by the Stockholm workshop scales. In addition, the relationships between the Stockholm workshop scales and each of the ten objective tests of hand function and the four hand symptom questions were explored.
PATIENTS AND METHODS
Subjects
The participants in this study (n=111) came from two subgroups, an industrial worker group and a patient group. In the industrial worker group (n=81) included all male workers exposed to vibration from hand-held tools, who worked at a heavy manufacturing plant in southern Sweden and had taken part in a workplace surveillance with a special focus in vibration investigation. Their median age was 40 (range 19–62) years and their median years of working with hand–arm vibration tools was 15 (range 1–45) years. The patient group (n=30) consisted of workers from various heavy occupations who had been consecutively referred to the Department of Hand Surgery with hand problems characterized by white fingers and/or sensory disturbances in the hand. Their median age was 47 (range 29–64) years and their median years of working with hand–arm vibration tools 26 (range 11–40) years. The workers represented several types of manual professions, including iron-plate workers, mechanics, carpenters, machine fitters, electricians, construction workers, building constructors and technicians. The most common type of hand-held tools used were pneumatic tools (75%), followed by pneumatic/electric tools (16%), and then electric tools (8%). These were grinders, chisel hammers, impact wrenches, fettling tools and drills. One hundred and three workers were right-handed and eight were left-handed.
Subjective outcomes
Stockholm workshop scales
The Stockholm workshop scales, neurological (Brammer et al., 1987) (Table 1) and vascular stages (Gemne et al., 1987) (Table 2), were proposed during an international congress of vibration experts in Stockholm 1986. This classification replaced the earlier Taylor–Pelmear classification (Taylor and Pelmear, 1975) in which both vascular and neurological symptoms were included. After a detailed medical and work history, a physical examination of the hands is performed to rule out other related disorders. These results are then used to reach a decision on the severity of Stockholm workshop staging for neurological (stages 0–3) and vascular (stages 0–4) symptoms.
Questions on hand symptoms
A question was asked regarding four hand symptoms not included in the Stockholm workshop scales; cold intolerance, pain, muscle cramp and weakness of grip. The question asked was “Have you been troubled by any of these (four) hand symptoms constantly, or on any occasion during the last 3 months?” Three symptoms, cold intolerance, pain and muscle cramp, were each scored on a four-graded scale, scored 1=none/ minor (mildest), 2=moderate, 3=disturbing and 4= hinders function (most severe) Rosén, 1996. One symptom, weakness of grip was scored dichotomously: yes or no.
Objective outcomes
Perception of touch/pressure
The Semmes-Weinstein monofilaments (Weinstein, 1993) were used to assess perception of touch/pressure and were used in the standardized way described by Bell-Krotoski (1995). A score of 0–5 was used; 5 for green filament, 4 for blue filament, 3 for purple filament, 2 for red filament (number 4.56), 1 for red filament (number 6.65), and 0 for not testable. Measurement at three critical sites for each of the median and ulnar nerves gave six critical sites for each hand and a maximum score of 30. Two cut-off limits (thresholds) were used in this study. The cut-off limit <30 for “normal” (green filament) in all six critical sites (Weinstein, 1968) and <25 for “diminished light touch” (blue filament) in the fingers. Recent research of Semmes-Weinstein monofilaments thresholds for the hands of normal subjects have revealed variations between green filament (number 2.83) and blue filament (number 3.61) (Birke et al., 2000).
Perception of vibration
Assessment of perception thresholds for vibration (tactilometry) within frequencies of 8–500 Hz was performed according to Lundborg et al. (1987, 1992). The index finger was investigated.
Tactile gnosis
Static two-point discrimination (s2PD) was measured as described by Moberg (1990). The instrument used was the Dellon Disk-CriminatorTM and an s2PD score of ≤5 mm was regarded as normal. The STI testTM (Shape/Texture Identification test) was performed according to Rosén and Lundborg (1998). Results from the index finger were used.
Dexterity
The Purdue pegboard test (Tiffin and Asher, 1948) tests finger dexterity and speed. The right- or left-hand subtest was used and the mean score of three consecutive trials was calculated and used in the analysis. A group of healthy subjects were recruited in order to obtain normative data for this test, as results from an earlier study (Cederlund et al., 1999) showed that existing normative values (Tiffin and Asher, 1948) were not applicable to that Swedish sample. The healthy subjects were 41 policemen who had not been exposed to vibration.
Grip function
The Sollerman hand function test was used for assessment of grip function (Sollerman and Ejeskär, 1995). This test consists of 20 tasks based on seven of the most frequently used hand grips in daily activities. This provides a picture of both the ability and quality of the hand. Three tasks which are especially difficult for subjects with vibration injury to carry out are: “picking up coins from a flat surface”, “putting nuts on bolts”, and “doing up buttons” (number 2, 8, 10). These three tasks were used in the study.
Grip strength/force
Grip- and pinch-strength were measured with a Jamar dynamometer and pinch gauge (palmar pinch) according to Mathiowetz et al. (1985). The mean value of three successive trials was calculated. Grip force was measured with the Grippit electronic instrument (AB Detektor, Gothenburg, Sweden). This is an electronic grip force measurement that measures the maximum momentary force (peak force) as well as the mean force (average) over a set period of time (10 s). The Grippit test was performed according to Nordenskiöld and Grimby (1993).
Study procedures
A vibration investigation was performed by a hand surgeon. This included a detailed medical and work history, including years of vibration exposure, and a physical examination of the hands. The examination consisted of inspection of both hands and Allen’s, Tinel’s and Phalen’s tests to rule out other related disorders. These results were then used to reach a decision on the severity of Stockholm workshop staging for neurological (stages 0–3) and vascular (stages 0–4) symptoms. In addition, all subjects took part in a hand assessment session starting with the four questions about subjective hand symptoms, followed by a hand assessment including ten tests of hand function which were performed in a standardized way by the first author (RC). In order to control for inter-tester bias, this examiner was unaware of the staging of the Stockholm workshop scales and the work history. Assessment of perception thresholds for vibration was carried out by a biomedical analyser on the same day. Data from the dominant hand were used in 107 cases and, in the four cases with unilateral problems, data from the affected, non-dominant hand were used.
Statistical methods
The results from all ten tests of hand function for each subject were compared with existing normative data and dichotomized as “pathological” or “not pathological”. For the Purdue pegboard test, the results were compared with those of the reference group and results beyond the fifth percentile were regarded as pathological. For four tests (the Jamar dynamometer, pinch gauge, Grippit (average 10 s) and Grippit (peak force)), the results were compared with existing age-related normative data, estimated in a one-sided 95% confidence interval. For five tests (the Semmes-Weinstein monofilaments, tactilometry, s2PD, Shape/texture identification test, and the Sollerman hand function test), the exposed group was compared with existing cut-off limits from normative data.
The four hand symptoms were dichotomized as pathological (disturbing, severe, hindering function) or not pathological (none or minor symptoms).
To analyse the ten objective tests of hand function and the four questions on subjectively perceived hand symptoms as related to the gold standard of the Stockholm workshop scales, their sensitivity and specificity (Yerushalmy, 1947) were calculated. Sensitivity is the proportion of patients with disease who have a positive test result. Specificity is the proportion of patients without disease who have a negative test result (Fletcher, 2000). The dichotomized tests of hand function and hand symptoms were analysed in relation to dichotomized Stockholm workshop scales data; in neurological vibration symptoms (stages 0 versus 1–3), and vascular vibration symptoms (stages 0 versus 1–4). A test with a sensitivity or specificity score of 1.00 (100%) indicates total agreement with the gold standard, and 0.80 indicate high agreement (McClure, 2001). The sensitivity and specificity scores were added together to give a combined sensitivity+specificity score.
To explore correlations between Stockholm workshop scales and tests of hand function and questions of hand symptoms, the Spearman rank correlation test was used. Because the scale directions of several of the variables in the explorative analysis were opposed, the results showed positive as well as negative correlations. The Bonferroni method reduces the risk of mass-significance when multiple tests are performed. In situations where tests and variables are highly correlated, the Bonferroni method is inappropriate as it is too rigid and may miss real differences (Bland and Altman, 1995). Instead, as carried out in this study, the risk can be reduced by lowering the significant level and only accepting correlations at a significance level of P<0.001.
Ethics
The study was approved by the Ethics Committee, Lund University.
RESULTS
The distributions of neurological and vascular symptoms, as classified by the Stockholm workshop scales for each subgroup are presented in Tables 1 and 2. Twenty-four workers had only neurological vibration symptoms (numbness, reduced dexterity), seven only vascular vibration symptoms (vibration white fingers), and 22 had a combination of both types of symptoms.
The ten tests of hand function revealed considerable variation in their relation to the Stockholm workshop scales. The sensitivity, specificity and combined sensitivity+specificity scores for each test are presented in Table 3. The tests with the highest combined agreement to the neurological Stockholm workshop scale were Semmes-Weinstein monofilaments (cut-off <25), tactilometry and Purdue pegboard test, while the lowest agreement was demonstrated for Sollerman hand function test (number 2, 8, 10) and the Semmes-Weinstein monofilaments (cut-off <30). The tests with the highest agreement to the vascular Stockholm workshop scale were tactilometry, Purdue pegboard test, and Shape/ texture identification test, while the lowest agreement was demonstrated for Sollerman hand function test and Semmes-Weinstein monofilaments (cut-off <30).
The sensitivity, specificity and combined sensitivity+specificity for the four questions on hand symptoms are presented in Table 4. Pain showed the highest and muscle cramp the lowest agreement to the neurological stages. Cold intolerance showed the highest and muscle cramp the lowest agreement to the vascular stages.
When exploring correlations between tests of hand function, hand symptoms and Stockholm workshop scales, all hand symptoms and five of the ten tests of hand function were significantly correlated to both scales (Table 5). The highest correlation was found between each of the subjective hand symptoms, (cold intolerance, pain and weakness in grip), and the Stockholm workshop scales. Among the objective tests of hand function, s2PD, tactilometry, Semmes-Weinstein monofilaments, Purdue pegboard test and Grippit (peak force) were significantly correlated to the Stockholm workshop scales. Though statistically significant, all correlation coefficients (r s) were moderate to low. No significant correlation was noted for the Shape/texture identification test, Sollerman hand function test, Jamar dynamometer, pinch gauge or Grippit (average 10 s).
DISCUSSION
The results of this explorative study demonstrate the difficulty in diagnosing HAVS. Five of the aspects of hand function that were assessed had a moderate-to-high agreement to the gold standard, the Stockholm workshop scales. These were perception of vibration, perception of touch/pressure, dexterity, cold intolerance and pain. It is concluded that defined objective tests and questions on specific hand symptoms, together with the Stockholm workshop scales, may be helpful in diagnosing HAVS.
The findings also indicated that some specific objective hand tests commonly used in vibration investigation today, such as the s2PD and Jamar dynamometer, have a lower agreement with the Stockholm workshop scales than other tests such as Semmes-Weinstein monofilaments (cut-off <25), and the Grippit electronic instrument (average 10 s). It is reasonable that tactile gnosis has lower agreement to Stockholm workshop scales than measures of peripheral perception of touch/pressure since the nerves in HAVS are in continuity with the sensory cortex of the brain (Merzenich and Jenkins, 1993).
As McGeoch et al. (1994) have pointed out, that no single objective test can provide valuable diagnostic information in HAVS, and that this can only be achieved by incorporating several objective tests of hand impairment (Kent et al., 1998; McGeoch et al., 1994). In our opinion, objective tests could be of use in our clinical work with these patients. Even if the Stockholm workshop scales are considered the gold standard in diagnosing HAVS, it should be remembered that they are measures of subjective outcomes. Objective tests may help to detect functional disturbances in the hand before the pathology manifests with subjective clinical symptoms.
An interesting finding was the differences in scores for Semmes-Weinstein monofilaments and the different cutoff limits for pathology. The higher cut-off limit is based on older normative data (Weinstein, 1968). The results in this study indicated that this cut-off limit seems too strict for workers with HAVS. By lowering the cut-off limit for diminished light touch (blue filament) in the fingers (Birke et al., 2000) a higher sensitivity and specificity in relation to the Stockholm workshop scales was obtained. It should however be kept in mind that it may be valuable to use the lower cut-off limit when diagnosing HAVS and the higher cut-off limit when describing early signs of pathological perception of touch/pressure.
The four questions on subjective hand symptoms showed higher sensitivity and specificity in relation to the Stockholm workshop scales than the objective tests of hand function. This may be due to the fact that the Stockholm workshop scales, as well as these specific questions, are based on the patient’s subjective experience of the condition.
One of the most interesting findings was that the cold intolerance score, when compared with the Stockholm workshop scale, vascular stages, showed high sensitivity and specificity. This was the best agreement among all the tests and symptoms investigated in this study, indicating that cold intolerance is strongly related to Stockholm workshop scale, vascular symptoms. The great problems that patients with HAVS may have with cold intolerance are also in line with our clinical experience. Our results support the Ministry of Labour in Japan and their recommendations to include “coldness of fingertips” in the Stockholm workshop vascular scale, as an early symptom of white fingers (Raynaud’s phenomenon) (Matoba et al., 1995). The importance of cold intolerance was also pointed out by Strömberg et al. (1996) who felt that cold intolerance should be included in assessment of vibration injuries as an early neurological symptom.
Our correlation analysis yielded information on whether the tests and symptoms in this study measured the same or different aspects of the disease. We could verify that all hand symptoms and tests of sensibility, perception of vibration and dexterity showed moderate associations to Stockholm workshop scales. Three out of the four tests of grip strength showed no correlation to Stockholm workshop scales, indicating that these tests measure different aspects of the disease.
It is important to decide what kinds of qualities a test should have to be clinically valuable (Altman, 1991). One central aspect to consider with any screening test is if it is more important to find pathology (sensitivity) or no pathology (specificity). A test with high sensitivity and low specificity can be utilized as a screening tool but further tests will be needed later to exclude normal cases, while a test with low sensitivity and high specificity is important when deciding about definite interventions (McClure, 2001). A test with both high sensitivity and specificity is the most useful test. No single objective test of hand function assessed in this study met the requirements for a diagnostic test, namely scores of more than 0.80 for both sensitivity and specificity. Only one subjective hand symptom – cold intolerance – had a combined score above 1.60, though pain (1.58) almost reached this criteria.
On the basis of our results, inquiry regarding cold intolerance and pain is useful in the diagnosis of HAVS. No tests of objective hand function showed evidence of value for the diagnosis of HAVS, but a number of tests showed moderate agreement and will be utilized in our clinical work and further research.
Footnotes
Acknowledgements
This study was supported by grants from the Swedish Council for Worklife Research, the Swedish Medical Research Council (No. 5188), and the Vårdal Foundation. Special thanks are extended to Lars Necking, Department of Hand Surgery, Malmö University Hospital, for conducting the vibration investigation, Ingrid Hallberg, Department of Hand Surgery, Malmö University Hospital, for technical assistance with the Tactilogram and Per-Erik Isberg, Department of Statistics, Lund University, for expert statistical advice.