In all ten patients with VWF and a prolonged Allen’s test who were included as participants in this study, structural arterial abnormalities of the hand were found according to MRA and/or ultrasound. This suggests the importance of arterial supply abnormalities in the pathophysiology of VWF.
Because of the study design, all participants had a prolonged Allen’s test and VWF (i.e., vascular) symptoms were more common than neurological symptoms. Usually, neurological symptoms are generally more common than vascular symptoms among workers exposed to vibration [24]. Earlier studies indicate that 15–37% of the general population have abnormalities in the superficial arterial arch of the hands [18, 19] compared to our study where all participants had imaging signs of any arterial abnormalities. There are also more recent indications highlighting the importance of vascular structural abnormalities in VWF. In an MRA case report by Poole et al., the three workers with VWF had vessel-occlusions, suspected to be caused by exposure to vibrations and the presence of vascular abnormalities in the form of nailfold capillaries has been demonstrated in RS [17, 25].
Furthermore, vibration-exposed workers with VWF have an increased frequency of a prolonged Allen’s test (about 50%) when compared to workers exposed to vibration without VWF [2, 23]. Impaired blood flow to the hands makes the arteries of the fingers more susceptible to cold exposure due to less warming because of less of an excess of warm blood and therefore, being more susceptible to cold-induced vasospasm. It might also be that the normal physiological constriction in cold weather produces a more pronounced decrease in circulation because of vascular abnormalities, which reduces the capability to maintain blood flow. Altogether, our findings are in line with previous research [17, 25]. It seems plausible that anatomical arterial abnormalities may, at least in part, be the cause of both VWF symptoms and the reduction of blood flow represented by the prolonged Allen’s test observed in this specific patient group and clinical setting. Hence, our data indicate that an underlying anatomical explanation for VWF should be suspected, at least when an Allen’s test is prolonged.
Other conditions that may present a clinical picture similar to Raynaud syndrome or VWF due to impaired blood flow are Thoracic outlet syndrome, Hypothenar hammer syndrome (HHS), Thenar hammer syndrome (THS) and Buerger’s disease, which are all associated with a partial or total blood flow impairment to the digits [7, 8]. HHS and THS are both caused by vascular obstruction, the ulnar artery (HHS), or the radial artery (THH), which is often secondary to trauma. These conditions can be accompanied by a whitening of the digits when exposed to cold and are difficult to distinguish from VWF, but may also contribute to its development [5, 7, 30]. In our participants, one (participant No 3) had signs of HHS on an MRA with an ulnar occlusion. Also, four (participants No 1, 2, 4 and 6) had tortuosity or a corkscrew appearance of the ulnar artery, which is a common radiological sign of HHS [3].
Interestingly, in this study, abnormalities found were mostly related to the superficial arterial arch. The thumb, which is usually most resistant to VWF and is rarely blanched except in severe cases gets its blood supply from the deep arch [6, 24]. This situation might be a protective factor for VWF of the thumb.
The correlation between ultrasound and MRA findings was low. Although ultrasound with a Doppler examination could detect the presence of anatomical abnormalities effectively, the indications regarding the specific location of stenosis were, in several cases, seemingly incorrect. Hence, it seems plausible that MRA could be a superior method to detect both the site of stenosis and underlying anatomical abnormalities in patients with VWF. In 90% of the patients examined in this study, an anatomical explanation could be detected using the magnetic resonance examination. This examination accurately locates the pathology and provides a wide range of information about vascular abnormalities, such as atypical vascular anatomy. We propose that this may improve diagnostic accuracy at earlier stages of the condition or in the future, even help to identify vibration-exposed subjects at risk of developing VWF. Since ultrasonography can also assess blood flow in vessels, it is unlikely that MRA should completely substitute an ultrasound examination in cases of VWF.
Conventional angiography is the gold standard for vascular abnormalities, but MRA yields comparable information about vascular anatomy, stenosis and obstruction [6]. Moreover, it is non-invasive and another potential advantage over conventional angiography is that MRA may identify connective tissue disorders, including vasculitis [6, 15]. On the other hand, conventional angiography is invasive, and complications from catheterisation make it less suited as a routine examination for VWF. However, MRA still uses intravenous gadolinium contrast [15, 25], but methods without contrast are under development [10, 11, 29]. In our study, the imaging from the non-contrast phase was inadequate for the study of arterial abnormalities.
A strength of this study is the thorough clinical examination of all study subjects included. Furthermore, the grading of symptoms and the assessment of the duration and intensity of exposure were carried out on an individual level. The patients originated from different regions of the country and worked in different companies, which is why it is unlikely that hereditary factors or particular local exposure influenced the outcome of the study. Also, the age in the group varied from 21 to 65 years, resulting in a mixed group representing vibration-exposed workers in a clinical setting.
Hence, we consider it an advantage by comparing the clinical symptoms with imaging of arterial blood flow displayed by two different techniques (ultrasonography and MRA). This enables a further understanding of the pathophysiology of VWF. Although vascular abnormalities were found in all patients, the design of the study cannot ascertain whether these were innate or acquired (because of vibration exposure). A prospective study has to be conducted with an MRA before the start of exposure to answer that question.
One limitation to this study is that although vascular abnormalities were found in all patients, the design of the study cannot ascertain whether these were innate or acquired (because of vibration-exposure). In order to verify causality, a prospective study would be required with angiographic examination before the start of exposure, but given the extended duration before the onset of symptoms, such a trial would be impractical. It would have been desirable with a randomised controlled study design. However, a randomised protocol would require a considerably larger patient cohort and would likely call for a multi-centre study to guarantee an adequate sample size. A control group, however, would have been especially beneficial for the interpretation of MRA examination results. Since the procedure is not customarily conducted in non-symptomatic subjects, there is limited knowledge about the average population’s anatomical variations without previous vibration exposure. We primarily selected the non-randomised protocol of this pilot study due to possible adverse effects of the phase contrast, which would be hard to motivate in a group of healthy control subjects. This study aimed at investigating whether there was an underlying anatomical pathology that could explain symptoms in VWF with a prolonged Allen’s test. There is some degree of potential selection bias due to the non-randomised inclusion, albeit that the consecutive inclusion of all patients fulfilled the study criteria during the period. On the other hand, according to their symptoms on the Stockholm workshop scale, few had severe symptoms.
There was no information on the use of gloves among the study participants. The use of gloves might reduce the risk for HHS, which is believed to be caused by repetitive blunt trauma that damages the vessels [1]. For arterial arch stenosis, there could be a protective factor in wearing gloves to decrease the grip pressure over the arterial arch in the hands, especially if the hand circulation depends on one arch.
Based on the findings of this study, we suggest that MRA is a suitable method to examine arterial abnormalities in the hands of patients with VWF and is complementary to ultrasound investigation. The method is relatively expensive, time-consuming, and associated with certain risks (due to intravenous contrast), although it is still considered safer than conventional angiography. In the future, the newly emerging techniques for non-contrast MRA [10] may change the cost-benefit balance of MRI in VWF. A more thorough and early investigation of patients’ hand arteries when there are signs and symptoms of VWF might be advantageous since our findings indicate a subgroup of VWF where symptoms depend on gross arterial abnormalities. This subgroup of VWF may thus, as already proposed [25], be advised to avoid exposure to hand-transmitted vibrations irrespective of their classification on the Stockholm workshop scale. Finally, some cases may benefit from the intervention of proximal stenosis.
In conclusion, this study reveals a high proportion of arterial stenosis and abnormalities in patients with VWF and a prolonged Allen’s test. We suggest that Magnetic Resonance Angiography could be beneficial, especially in combination with ultrasonography to better understand the underlying causes and arterial anatomy in patients with VWF. However, longitudinal studies comparing larger group of workers with different vibration exposures are needed to establish this method as a clinical tool.