Neurophysiological investigation of hands damaged by vibration: comparison with idiopathic carpal tunnel syndrome

Pain mechanisms in carpal tunnel syndrome: a systematic review and meta-analysis of quantitative sensory testing outcomes

ABSTRACT

Carpal tunnel syndrome (CTS) is the most common nerve compression in the arm. A mix of peripheral and central contributions on quantitative sensory testing (QST) has been reported in the literature. Thus, this systematic review or meta-analysis aimed to identify the dominant sensory phenotype and draw conclusive evidence about the presence of central sensitization (CS) in CTS. Based on an a priori published protocol and using PRISMA guidelines, 7 databases were searched (Embase, Web of Science, Scopus, PubMed, SAGE, EBSCOhost, and ProQuest). Eligible studies compared the QST findings of individuals with subacute and chronic CTS with those of healthy controls through thermal, mechanical, and vibration detection thresholds; thermal, pressure, and mechanical pain thresholds; mechanical pain sensitivity; presence of allodynia; wind-up ratio; and conditioned pain modulation. Thirty-seven studies were included in the qualitative analysis. Results showed a significant loss of all detection thresholds of hand median nerve territories and hand extramedian areas (little finger and hand dorsum) in CTS (P < 0.05) but no significant difference (P > 0.05) in wind-up ratio, cold, heat, or mechanical pain thresholds of the median nerve territories. Furthermore, there was a significant increase in mechanical pain sensitivity in median nerve territories and remotely in the forearm (P < 0.05) and a significant gain in pressure and heat pain thresholds in the carpal area (P < 0.05). Conditioned pain modulation was impaired in CTS. Hypoesthesia and increased thermal and mechanical pain ratings are the dominant sensory phenotype with inconclusive evidence about CS in CTS due to the heterogenous results of thermal and mechanical pain thresholds.

Working hand syndrome: A new definition of non-classified polyneuropathy condition

The aim of this paper was to define an unexplained non-classified polyneuropathy condition as a new neurological disease. This new diagnosis of occupation related polyneuropathy has been named as "WORKING HAND SYNDROME (WHS)."This study collected and compared clinic and electrophysiological analyze data from healthy controls, WHS patients, carpal tunnel syndrome (CTS) patients and polyneuropathy patients. The WHS patients presented to the clinic with pain, numbness, tingling, and burning sensations in their hands that increased significantly during rest and nighttime. However, there was no weakness in the muscles, and the deep tendon reflexes were normal in this disease. The patients had all been working in physically demanding jobs requiring the use of their hands/arms for at least 1 year, but no vibrating tools were used by the patients. All of the cases were men. I supposed that overload caused by an action repeated chronically by the hand/arm may impair the sensory nerves in mentioned hand/arm. In patients with these complaints, for a definitive diagnosis, similar diseases must be excluded. Nonetheless, the specific electrophysiological finding that the sural nerves are normal on the lower sides, as well as the occurrence of sensory axonal polyneuropathy in the sensory nerves without a significant effect on velocity and latency in the work-ups of the upper extremity are enough to make a diagnosis.In conclusion, WHS has been defined as a polyneuropathy and occupational disease. Patients with WHS present with pain, numbness, tingling, and burning sensations in their hands that increases significantly during rest and nighttime. They also use their arms/hands for jobs that require heavy labor. The neurological examinations of patients with WHS are normal. Only the sensory nerves in the upper extremities are affected. This article is suggested to serve as a resource for patients, health care professionals, and members of the neurology community at large.

Low myelinated nerve-fibre density may lead to symptoms associated with nerve entrapment in vibration-induced neuropathy

Prolonged exposure to hand-held vibrating tools may cause a hand-arm vibration syndrome (HAVS), sometimes with individual susceptibility. The neurological symptoms seen in HAVS are similar to symptoms seen in patients with carpal tunnel syndrome (CTS) and there is a strong relationship between CTS and the use of vibrating tools. Vibration exposure to the hand is known to induce demyelination of nerve fibres and to reduce the density of myelinated nerve fibres in the nerve trunks. In view of current knowledge regarding the clinical effects of low nerve-fibre density in patients with neuropathies of varying aetiologies, such as diabetes, and that such a low density may lead to nerve entrapment symptoms, a reduction in myelinated nerve fibres may be a key factor behind the symptoms also seen in patients with HAVS and CTS. Furthermore, a reduced nerve-fibre density may result in a changed afferent signal pattern, resulting in turn in alterations in the brain, further prompting the symptoms seen in patients with HAVS and CTS. We conclude that a low nerve-fibre density lead to symptoms associated with nerve entrapment, such as CTS, in some patients with HAVS.

Nerve conduction in relation to vibration exposure - a non-positive cohort study

BACKGROUND

Peripheral neuropathy is one of the principal clinical disorders in workers with hand-arm vibration syndrome. Electrophysiological studies aimed at defining the nature of the injury have provided conflicting results. One reason for this lack of consistency might be the sparsity of published longitudinal etiological studies with both good assessment of exposure and a well-defined measure of disease. Against this background we measured conduction velocities in the hand after having assessed vibration exposure over 21 years in a cohort of manual workers.

METHODS

The study group consisted of 155 male office and manual workers at an engineering plant that manufactured pulp and paper machinery. The study has a longitudinal design regarding exposure assessment and a cross-sectional design regarding the outcome of nerve conduction. Hand-arm vibration dose was calculated as the product of self-reported occupational exposure, collected by questionnaire and interviews, and the measured or estimated hand-arm vibration exposure in 1987, 1992, 1997, 2002, and 2008. Distal motor latencies in median and ulnar nerves and sensory nerve conduction over the carpal tunnel and the finger-palm segments in the median nerve were measured in 2008. Before the nerve conduction measurement, the subjects were systemically warmed by a bicycle ergometer test.

RESULTS

There were no differences in distal latencies between subjects exposed to hand-arm vibration and unexposed subjects, neither in the sensory conduction latencies of the median nerve, nor in the motor conduction latencies of the median and ulnar nerves. Seven subjects (9%) in the exposed group and three subjects (12%) in the unexposed group had both pathological sensory nerve conduction at the wrist and symptoms suggestive of carpal tunnel syndrome.

CONCLUSION

Nerve conduction measurements of peripheral hand nerves revealed no exposure-response association between hand-arm vibration exposure and distal neuropathy of the large myelinated fibers in a cohort of male office and manual workers.

Syndromes from segmental vibration and nerve entrapment: observations on case definitions for carpal tunnel syndrome

OBJECTIVES

The purpose of this paper is to assess the overlap and stability of two different case definitions of carpal tunnel syndrome CTS. The analysis considers the association between different case definitions and objective tests (sensory nerve conduction velocities, SNCVs and vibrotactile perception thresholds, TTS), and the natural history of CTS, in the context of two vibration-exposed cohorts.

METHODS

Clinical CTS cases were defined in two ways: (1) by the study physician using fixed criteria, and; (2) by questionnaire and hand diagram. SNCV in median and ulnar nerves was measured for digital, transpalmar, and transcarpal segments, and conventionally as from wrist-digit. Skin temperature was assessed as a point measurement by thermistor and regionally by thermal imaging. VTTs were determined at the bilateral fingertips of the third and fifth digits using a tactometer meeting the requirements of ISO 13091-1 (ISO 2001). The subjects were cohorts of shipyard workers in 2001 and 2004, and dental hygienists in 2002 and 2004.

RESULTS

Results are reported for 214 shipyard workers in 2001 and 135 in 2004, and for 94 dental hygienists in 2002 and 66 in 2004. In 2001, 50% of shipyard workers were diagnosed as CTS cases by at least one of the diagnostic schemes, but only 20% were positive by both criteria. Among study physician diagnosed cases, 64% were CTS negative in 2001, 76% were negative in 2004, 13% were positive in both years, 22% became negative after being positive, and 11% became positive after being negative. For only study physician diagnosed CTS did VTTs differ between cases differ and non-cases in digit 3; there was no such distinction in digit 5. The dental hygienists had little CTS.

CONCLUSION

Clinical case definitions of CTS based on diagrams and self-assessment, and clinical evaluation have limited overlap. Combining clinical criteria to create a more narrow or specific case definition of CTS does not appear to predict SNCV. The natural history of CTS suggests a protean disorder with considerable flux in case status over time.

Vascular and nerve damage in workers exposed to vibrating tools. The importance of objective measurements of exposure time

The aim of the present study was to compare the development of vibration white fingers (VWF) in workers in relation to different ways of exposure estimation, and their relationship to the standard ISO 5349, annex A. Nineteen vibration exposed (grinding machines) male workers completed a questionnaire followed by a structured interview including questions regarding their estimated hand-held vibration exposure. Neurophysiological tests such as fractionated nerve conduction velocity in hands and arms, vibrotactile perception thresholds and temperature thresholds were determined. The subjective estimation of the mean daily exposure-time to vibrating tools was 192 min (range 18-480 min) among the workers. The estimated mean exposure time calculated from the consumption of grinding wheels was 42 min (range 18-60 min), approximately a four-fold overestimation (Wilcoxon's signed ranks test, p<0.001). Thus, objective measurements of the exposure time, related to the standard ISO 5349, which in this case were based on the consumption of grinding wheels, will in most cases give a better basis for adequate risk assessment than self-exposure assessment.

Biochemical evaluation of serum and flexor tenosynovium in carpal tunnel syndrome

In total, 41 consecutive patients with "idiopathic carpal tunnel syndrome" and abnormal electrophysiologic findings who underwent carpal tunnel release were studied prospectively. The focus of this investigation was the evaluation of the levels of specific chemical mediators within the serum and flexor tenosynovium of these patients. Blood was collected from these patients within 1 week prior to carpal tunnel release, and flexor tenosynovium was obtained at time of surgery. Specimens were then analyzed to determine the levels of interleukins 1 and 6, prostaglandin E(2) (PGE(2)), and malondialdehyde bis diethyl acetal. These values were compared to those of controls who had no evidence of carpal tunnel syndrome. A significant increase was noted in the serum malondialdehyde and tenosynovial levels of malondialdehyde, interleukin 6, and prostaglandin PGE(2) compared to controls. The elevated levels of these biologic factors and the absence of interleukin 1 elevation support a noninflammatory ischemia-reperfusion etiology for so-called "idiopathic carpal tunnel syndrome" that causes progressive edema and fibrosis of the tissues within the carpal canal. These findings correlate with previous histopathology reports. We believe that "idiopathic carpal tunnel syndrome" is an "-osis" not an "-itis."

Hand-arm vibration syndrome in Swedish car mechanics

AIMS

To assess the occurrence of hand-arm vibration syndrome (HAVS) in Swedish car mechanics, and the relation between HAVS and duration of exposure.

METHODS

A total of 806 mechanics answered a questionnaire on vascular and neurological symptoms, and exposure to vibrations. Mechanics with symptoms, and some mechanics without symptoms, were invited to a clinical examination, including also a timed Allen test. Vascular and neurological symptoms were classified using the Stockholm Workshop scales. The mean daily exposure (mainly using nut-runners) was 14 minutes and the mean exposure duration, 12 years. Published data have shown vibration levels in nut-runners of about 3.5 m/s(2).

RESULTS

In the questionnaire, 24% reported cold induced white finger (WF), 25% persistent numbness, and 13%, reduced grip force. The clinical examination showed a prevalence of vibration induced white finger (VWF) of about 15%, mainly in stage 2, and after 20 years, of 25%. A survival analysis showed similar results. We found that the International Organisation for Standardisation (ISO) model underestimates the risk of VWF. The incidence after 1975 was 19 cases per 1000 person-years. Slow refill times in the timed Allen test were common (15% had a refill time of >20 seconds), and associated with the presence of VWF. The clinical examination revealed neurological symptoms in the hands in about 25% of subjects, mainly at stage 2. After 20 years, the prevalence was 40%. The questionnaire items on WF and numbness both showed likelihood ratios of 13.

CONCLUSION

HAVS is common among Swedish car mechanics in spite of short daily exposure times. This underlines the need for preventive measures.

Hand-arm-vibration syndrome (HAVS): is there a central nervous component? An fMRI study

Hand-held vibrating tools may result in neuromuscular dysfunction and vasospastic problems of the hand. Sensory and motor dysfunction can be explained by injury to peripheral structures, but could also be due to changes in cortical somatotopic mapping of the hand in the brain. The purpose of the present study was to use functional magnetic resonance imaging (fMRI) to assess the somatotopic cortical representation of the hands of workers subjected to occupational vibration. The study included six men with severe vibration exposures who were suffering from hand-arm-vibration syndrome (HAVS) and six controls. The analysis focused on the pattern and degree of activation of contra- and ipsilateral hemispheres of the brain with tactile stimulation and motor activation of the hand. These stimulations resulted in well-defined activation of the contralateral, and to a lesser extent the ipsilateral hemisphere. Statistical analysis of this limited patient material did not indicate any significant somatotopic cortical changes following long-term exposure to vibrating hand-held tools, although there was a tendency to a shift of activation towards the more cranial parts of the cortex in the patient group.

Cutaneous sensory nerve fibers are decreased in number after peripheral and central nerve damage

Two dermatologic patients displaying peripheral and central nerve damage, respectively, are described. Cutaneous nerve fibers in both patients were studied in skin biopsy specimens taken from neuropathic areas and from the contralateral side, immunocytochemistry being applied to a pan-neuronal marker, a protein gene-product (PGP 9.5). One of the patients, suffering from compression of the ulnar nerve, had dyshidrotic eczema of the hands that was absent on areas of skin that were neuropathic. The cutaneous innervation (most of which was sensory) was reduced by 50% in the neuropathic area as compared with the contralateral side. The other patient had unilateral pruritus on the parethic side after a stroke. The cutaneous innervation of that side was reduced by 80% as compared with the other side. It seems that peripheral sensory innervation is a prerequisite for inflammation, whereas spontaneous itching may emanate from a central nervous system disorder such as a stroke and continue on in partly denervated skin.

Vibration-induced hand problems: role of the peripheral nerves in the pathophysiology

A substantial number of people who are exposed to vibrating hand-held tools develop vasospastic and sensorineural symptoms that may seriously affect the ability to work. Apart from the discomfort of the disease itself, this leads to socioeconomic problems for the patients and high costs for the society. The diagnosis of the neurological symptoms is sometimes difficult and may be misinterpreted as a nerve compressive disorder such as carpal tunnel syndrome, which may also develop. This review summarises our available knowledge about the pathophysiology of the neurological dysfunction with reference to hand problems after exposure to vibrating hand-held tools.

The prevalence of sensorineural symptoms attributable to hand-transmitted vibration in Great Britain: a national postal survey

BACKGROUND

Exposure to hand-transmitted vibration (HTV) can cause sensorineural symptoms in the upper limb, but its impact has not previously been assessed in the general population.

METHODS

To investigate, we mailed a questionnaire about exposures to HTV, finger blanching and sensory symptoms (numbness or tingling) in the upper limbs to a population sample comprising 21,201 working-aged men and women selected at random from the age-sex registers of 34 British general practices, and a further 993 randomly selected from the pay records of the armed services. Associations were explored using multiple logistic regression models to adjust for confounding, with the resultant odds ratios converted into prevalence rate ratios (PRs).

RESULTS

Of 12,907 respondents, 2,607 (20.2%) reported sensory symptoms in the upper limb during the past week. Sensory symptoms were more prevalent in those with blanching, and were commonly associated with exposure to HTV, especially in men. In comparison with men who had never been exposed to HTV, the PR in men exposed both at work and in leisure was 2.2 (95% CI 1.9-2.4). Associations were found even in those who had never blanched.

CONCLUSIONS

Sensorineural symptoms in the upper limbs are common. HTV is an important risk factor for such complaints in the general population.

Multifocal neural conduction impairment in forestry workers exposed and not exposed to vibration

OBJECTIVE

The aim of the study was to assess peripheral neural involvement induced by exposure to hand-arm vibration.

METHODS

Twenty lumberjacks, working regularly with chain-saws and exposed to hand-arm vibration (group E) and 20 forestry workers performing heavy manual work and not exposed to vibration (group NE) were matched with a control group of 20 healthy non-manual workers (group C). The subjects of groups E and NE, all symptomatic, and of group C underwent extensive bilateral neurophysiological examination consisting of: sensory conduction (velocity and amplitude) of radial, median and ulnar nerves in digit-wrist segments; sensory conduction (velocity) of median nerve in wrist-elbow segment; mixed conduction (velocity and amplitude) of median and ulnar nerves in palm-wrist segments; motor conduction velocity, including distal motor latencies, and amplitude of median (elbow-wrist) and ulnar (elbow-wrist and across the elbow) nerves.

RESULTS

Electrophysiological abnormalities were found in 85% of group E's limbs, versus 62.5% of group NE's limbs. The most frequent pathological pattern in group E was a 'multifocal' impairment (multiple sites of several nerve segments), with a prevalent involvement of sensory rather than motor fibres in the hand, seldom extending to the forearm. Multivariate analysis showed that the neurographic parameters which better characterized workers exposed to hand-arm vibration had a pattern different from that usually found in idiopathic carpal tunnel syndrome (CTS).

CONCLUSION

These results suggest that vibration-induced neural involvement can be considered neither pure digital neuropathy, nor definite CTS, as previously described.

Neurophysiological findings in vibration-exposed male workers

Fractionated nerve conduction, vibrotactile sense, and temperature thresholds were studied in 73 symptomatic vibration-exposed male workers. Three symptomatic groups were distinguished: patients with isolated sensorineural symptoms; with isolated vasospastic problems; and with both. Clinical carpal tunnel syndrome occurred in 14 patients and abnormal cold intolerance (without blanching of the fingers) in 23. In the group as a whole, nerve conduction studies were abnormal in the median nerve but not in the ulnar nerve and vibration perception and temperature thresholds were impaired. Of the three symptomatic groups, patients with isolated sensorineural symptoms differed from controls. No differences were seen between patients with and without clinical carpal tunnel syndrome. With severe sensorineural symptoms the vibration perception thresholds, but not the values of the nerve conduction studies, were further impaired. The results indicated two injuries that are easily confused: one at receptor level in the fingertips and one in the carpal tunnel. Careful clinical assessment, neurophysiological testing, and examination of vibrotactile sense are required before carpal tunnel release should be considered in these patients.

Patient satisfaction and return to work after endoscopic carpal tunnel surgery

One hundred twenty-eight patients with idiopathic carpal tunnel syndrome were evaluated before surgery and 3 and 6 months after unilateral endoscopic carpal tunnel release. The variables analyzed included patient demographics, symptoms and signs, activities of daily living (ADL), sensibility and strength measurements, preoperative distal motor latency of the median nerve, operating surgeon, postoperative palmar pain and tenderness, return to work, and patient satisfaction with the results of surgery. Multivariate statistical analyses were performed, with patient satisfaction at 6 months after surgery and the time until return to work after surgery as the dependent variables. On stepwise logistic regression analysis of all preoperative variables, significant predictors of patient dissatisfaction at 6 months after surgery were higher age, heavy vibration exposure, worse ADL score, and better distal motor latency. Analysis of all preoperative and 3-month postoperative variables showed heavy vibration exposure, better distal motor latency, and worse 3-month postoperative ADL score to have the strongest independent correlation with patient dissatisfaction at 6 months. No significant independent association was found between any of the preoperative variables studied and the length of time until return to work after surgery.

Sensory function after median nerve decompression in carpal tunnel syndrome. Preoperative vs postoperative findings

The sensory recovery was monitored for up to 1 year after decompression of the median nerve in 69 patients with carpal tunnel syndrome. Special attention was paid to the rate of recovery, the importance of constant or intermittent numbness or paraesthesiae preoperatively and the influence of gender. Most patients with numbness/paraesthesiae and those with abnormal two-point discrimination recovered within 10 days. Perception of touch and vibration recovered within 3 weeks in most patients but those with abnormal nerve conduction/sensory amplitude recovered slowly during follow-up. After 1 year patients with intermittent preoperative symptoms were significantly more likely to achieve normal nerve conduction and perception of touch. Women were more likely to achieve normal nerve conduction and perception of touch. A comparison of recovery between matched men and women with identical preoperative status showed no significant difference. The results indicate the importance of early treatment of carpal tunnel syndrome.

Displacement and strain of the median nerve at the wrist

Median nerve displacement and strain in the carpal tunnel region were measured as functions of wrist position and carpal tunnel pressure in 5 cadaver forearms during simulated active finger flexion. The positions of spherical stainless-steel markers embedded within the median nerve and flexor digitorum superficialis of the long finger were measured in 3 dimensions by a radiographic direct linear transformation technique. Each limb was tested in 3 wrist positions (60 degrees extension, neutral, and 60 degrees flexion) and 4 carpal tunnel pressures (0, 30, 60, and 90 mmHg). Carpal tunnel pressure was controlled with a balloon angiocatheter inserted deep to the flexor digitorum profundus. The ratio of median nerve to flexor tendon excursion was linear and was affected by wrist position but not carpal tunnel pressure. Patterns of strain in the median nerve proximal to the flexor retinaculum were different from those of strain within the carpal tunnel. Nerve strains were affected by wrist position, but carpal tunnel pressure had no effect. The hydrostatic pressure effect associated with carpal tunnel syndrome does not appear to influence median nerve kinetics or kinematics for the wrist positions studied.

Structural nerve changes at wrist level in workers exposed to vibration

OBJECTIVES

To analyse the character of morphological changes occurring in a well defined peripheral nerve in humans exposed to vibration from hand held tools.

METHODS

Biopsies of the dorsal interosseus nerve just proximal to the wrist were taken from 10 men exposed to vibration and from 12 male age matched necropsy controls. The nerve was resected for pain relief either as the sole procedure or in conjunction with carpal tunnel release. All specimens were sectioned and examined by light microscopy in standard sections, thin epon sections, and teasing preparations.

RESULTS

The combined results of the analyses showed pathological changes in all 10 patients dominated by breakdown of myelin and by interstitial and perineurial fibrosis. All but one of the 12 controls were normal.

CONCLUSION

These findings often show severe nerve injury previously not described at this level. They indicate that demyelination may be the primary lesion in neuropathy induced by vibration followed by fibrosis associated with incomplete regeneration or with organisation of oedema. Vibration can induce structural changes in peripheral nerves just proximal to the wrist and such changes may constitute a structural component in carpal tunnel syndrome among people exposed to vibration. This may help to explain the poor results achieved by carpal tunnel release in these patients.

Digital sensory nerve conduction velocity and vibration perception threshold in peripheral neurological test for hand-arm vibration syndrome

To evaluate peripheral neuropathy in patients with vibration syndrome, an examination was conducted of sensory nerve conduction velocity (SCV) in the digital segment of the median nerve in the middle finger and vibration perception threshold (VPT) at 125 Hz on the same middle fingertip. In addition, possible correlations were investigated between the two measurements. SCVs in the digital segment were measured by stimulating at the wrist electrically and recording from two pairs of electrodes in the finger. Fractionated SCVs were also measured in the palm-to-finger, wrist-to-palm, and elbow-to-wrist segments. The subjects were 52 patients with vibration syndrome and 40 healthy controls of similar age. SCVs in the digital segment and the wrist-to-palm segment were significantly slower in the patients than in the controls, and VPTs were higher in the patients. The strongest correlation of VPTs with SCVs among nerve segments measured was shown in the digital segment. With an increase in VPTs, SCVs in the digital segment tended to be slower, and slowed digital SCVs were encountered more frequently: 13% in VPTs below 5.0 dB and 56% in VPTs above 17.5 dB. Slowed digital SCVs were found in 43% of the patients and increased VPTs were encountered in 92%.

Hand problems in 100 vibration-exposed symptomatic male workers

Long-term use of hand-held vibrating tools may induce various types of hand problems. One hundred symptomatic men exposed to vibration from such tools were interviewed and examined with special reference to neurosensory and vasospastic problems. Three distinct symptomatic groups were identified: isolated neurosensory symptoms (48%), isolated vasospastic problems (20%), and combined neurosensory and vasospastic problems (32%). Abnormal cold intolerance (pain and coldness without blanching of the fingers on exposure to cold) occurred in 27% of the patients. Neurosensory problems were more predominant than vasospastic ones, especially during the first 20 years of vibration exposure. Of 80 patients with neurosensory symptoms, only 22 had signs of a carpal tunnel syndrome (CTS). It is concluded that vibration-induced neurosensory and vasospastic symptoms can occur separately or together, and that the neurosensory symptoms are often not due to a CTS.