Changes in the forearm associated with median nerve compression at the wrist in the guinea-pig

The Structure of the Brachial Plexus of the Djungarian Hamster (Phodopus sungorus)

Hamsters are often chosen as companion animals but are also a group of animals frequently subjected to laboratory tests. As there are no scientific publications providing information on the anatomical architecture of the brachial plexus of the Djungarian hamster, this study analyses the structure of this part of the nervous system of this species. It is important to know the details of this structure not only for cognitive reasons, but also due to the increasing clinical significance of rodents, which are often used in scientific research. The study was conducted on 55 specimens. Like in humans, the brachial plexus of the Djungarian hamster has three trunks. The following individual nerves innervating the thoracic limb of the Djungarian hamster: the radial nerve, median nerve, ulnar nerve, musculocutaneous nerve, axillary nerve, suprascapular nerve, thoracodorsal nerve, cranial pectoral nerves, caudal pectoral nerve, lateral thoracic nerve, long thoracic nerve, and subscapular nerves. Similarly to other mammals of this order, the brachial plexus of the Djungarian hamster ranges widely (C5-T1). However, its nerves are formed from different ventral branches of the spinal nerves than in other mammals.

Reduction in median nerve cross-sectional area at the forearm correlates with axon loss in carpal tunnel syndrome

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The median nerve CSA at the forearm is smaller when CTS is involved with axon loss.

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WFR of the median nerve is highest when CTS causes slight axon loss.

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Axon loss of the median nerve in CTS hampers the diagnostic value of wCSA and WFR.

Objective

To explore the relationship between axon loss and measured cross-sectional areas of the median nerve (MN) in severe carpal tunnel syndrome (CTS).

Methods

In this retrospective study of 158 examined wrists, we compared axon loss to the ultrasound parameters MN cross-sectional area at the wrist (wCSA), MN cross-sectional area at the forearm (fCSA) and wrist-to-forearm ratio (WFR), in patients with moderate to extreme CTS. Axon loss was evaluated by needle electromyography (EMG) of the abductor pollicis brevis muscle (spontaneous activity and reduction of interference pattern).

Results

Both the spontaneous activity and interference pattern reduction correlated negatively to fCSA (r = −0.189, p = 0.035; r = −0.210, p = 0.019; respectively). In moderate CTS, both the spontaneous activity and interference pattern reduction correlated positively to WFR (r = 0.231, p = 0.048; r = 0.232, p = 0.047; respectively). The WFR was highest when slight spontaneous activity was detected. Neither wCSA nor WFR correlated with axon loss in severe and extreme CTS.

Conclusions

The fCSA is smaller when axon loss in CTS is more prominent. The WFR is highest when CTS is associated with slight axon loss of the MN.

Significance

CTS might cause retrograde axonal atrophy detected as small fCSA. Prominent axon loss in CTS may reduce the diagnostic value of WFR.

Characteristics of forearm mixed nerve conduction study in carpal tunnel syndrome: Comparison with ultrasound assessments

This study aimed to characterize forearm mixed nerve conduction study (NCS) findings in carpal tunnel syndrome (CTS). Eighty-two patients with CTS and 48 healthy controls were enrolled. We directly compared the forearm mixed NCS and ultrasonography results from CTS patients with those from the controls. Correlation analyses were performed to identify the relationship between forearm mixed NCS parameters and ultrasound measurements in CTS. We observed reduced forearm mixed nerve amplitude and increased cross-sectional area (CSA) of the median nerve at the proximal carpal tunnel (CT) inlet in CTS. The forearm mixed nerve amplitude negatively correlated with the CSA at the proximal CT inlet. We found a negative correlation between Bland's neurophysiological grade and the forearm mixed nerve amplitude as well as a positive correlation between the CSA of the median nerve at the proximal CT inlet and Bland's neurophysiological grade. We confirmed that the reduced median mixed nerve amplitude is the distinguishing feature of forearm mixed NCS in CTS. Our findings suggest that the forearm mixed NCS is potentially useful in evaluating its severity.

Chronic peripheral nerve compression disrupts paranodal axoglial junctions

INTRODUCTION

Peripheral nerves are often exposed to mechanical stress leading to compression neuropathies. The pathophysiology underlying nerve dysfunction by chronic compression is largely unknown.

METHODS

We analyzed molecular organization and fine structures at and near nodes of Ranvier in a compression neuropathy model in which a silastic tube was placed around the mouse sciatic nerve.

RESULTS

Immunofluorescence study showed that clusters of cell adhesion complex forming paranodal axoglial junctions were dispersed and overlapped frequently with juxtaparanodal components. These paranodal changes occurred without internodal myelin damage. The distribution and pattern of paranodal disruption suggests that these changes are the direct result of mechanical stress. Electron microscopy confirmed loss of paranodal axoglial junctions.

CONCLUSIONS

Our data show that chronic nerve compression disrupts paranodal junctions and axonal domains required for proper peripheral nerve function. These results provide important clues toward better understanding of the pathophysiology underlying nerve dysfunction in compression neuropathies. Muscle Nerve 55: 544-554, 2017.

Proximal axonal changes after peripheral nerve injury in man

Peripheral nerve injury leads to changes in the proximal axon. Traumatic nerve injuries in humans were investigated to characterize such electrophysiological changes. Mixed nerve conduction studies (MNCS) and motor conduction studies (MCS) were performed proximal to the injury. Control values were obtained from the uninjured limb. Median (n = 24) and ulnar (n = 35) nerve injuries were studied. The injured nerves had significant mixed nerve action potential (MNAP) amplitude reductions (median: P < 0.0001; ulnar: P < 0.0001). The majority of the MNAP amplitude reductions were severe and early. There was slowing in the mixed nerve conduction velocity (MNCV) (median: P = 0.09; ulnar: P = 0.04) and motor conduction velocity (MCV) (median: P = 0.046; ulnar: P = 0.005). Axonal loss appears to play a significant role in producing the MNCS changes observed, and its early occurrence is noteworthy. Proximal MCV reduction could be secondary to the effects of injury as well as collateral sprouting of uninjured axons. Proximal axonal changes may have an impact on recovery.

Does retrograde axonal atrophy really occur in carpal tunnel syndrome patients with normal forearm conduction velocity?

OBJECTIVE

The cause of decreased median forearm motor conduction velocity (FMCV) in carpal tunnel syndrome (CTS) is best ascribed to retrograde axonal atrophy (RAA); however, the relationships between the occurrence of RAA and electrophysiological or clinical severity remains controversial. We attempt to determine whether RAA really occurs in CTS patients with normal median FMCV and to investigate any relationships between RAA and severity of compression at the wrist.

METHODS

Consecutive CTS patients were enrolled and age-matched volunteers served as controls. We performed conventional nerve conduction studies (NCS) and measured median and ulnar distal motor latencies (DML), FMCV, compound muscle action potential (CMAP) amplitudes, distal sensory latencies (DSL), and sensory nerve action potential (SNAP) amplitudes. Furthermore, palmar median stimulation was done to calculate the wrist-palm motor conduction velocity (W-P MCV). Patients included for analysis should have normal FMCV and needle examination. We compared each electrodiagnostic parameters between the patient group and controls.

RESULTS

The mean+/-SD of the W-P MCV for patients and controls were 33.26+/-6.74 and 52.14+/-5.85 m/s and those of median FMCV were 55.26+/-3.56 and 57.82+/-3.9 m/s, respectively. There was a significant reduction in the W-P MCV (36.2%, P<0.00001), significant decrease in the median FMCV (4.43%, P<0.00001) and SNAP amplitudes, and an increase of the DML and DSL in the patient group (P<0.00001) compared to the controls; however, there were no differences in median and ulnar CMAP amplitudes, ulnar FMCV and DML between the controls and patients.

CONCLUSIONS

RAA and relatively slowed median FMCV do occur in CTS patients with normal median FMCV, regardless of severity of clinical manifestations and electrophysiological abnormalities.

SIGNIFICANCE

This article provides new information for research of the electrophysiological changes of the proximal nerve part at distal injury.

Work-related musculoskeletal disorders of the hand and wrist: epidemiology, pathophysiology, and sensorimotor changes

The purpose of this commentary is to present recent epidemiological findings regarding work-related musculoskeletal disorders (WMSDs) of the hand and wrist, and to summarize experimental evidence of underlying tissue pathophysiology and sensorimotor changes in WMSDs. Sixty-five percent of the 333 800 newly reported cases of occupational illness in 2001 were attributed to repeated trauma. WMSDs of the hand and wrist are associated with the longest absences from work and are, therefore, associated with greater lost productivity and wages than those of other anatomical regions. Selected epidemiological studies of hand/wrist WMSDs published since 1998 are reviewed and summarized. Results from selected animal studies concerning underlying tissue pathophysiology in response to repetitive movement or tissue loading are reviewed and summarized. To the extent possible, corroborating evidence in human studies for various tissue pathomechanisms suggested in animal models is presented. Repetitive, hand-intensive movements, alone or in combination with other physical, nonphysical, and nonoccupational risk factors, contribute to the development of hand/wrist WMSDs. Possible pathophysiological mechanisms of tissue injury include inflammation followed by repair and/or fibrotic scarring, peripheral nerve injury, and central nervous system reorganization. Clinicians should consider all of these pathomechanisms when examining and treating patients with hand/wrist WMSDs.

Performance of a high-repetition, high-force task induces carpal tunnel syndrome in rats

STUDY DESIGN

A randomized controlled prospective experimental study with some repeated measures.

OBJECTIVES

To characterize behavioral, sensory, motor, and nerve conduction decrements, and histological changes in the median nerve in rats trained to perform a high-force repetitive task.

BACKGROUND

Understanding of work-related carpal tunnel syndrome is hampered by the lack of experimental studies of the causes and mechanisms of nerve compression induced by repetitive motion. Most animal models of nerve compression have not employed voluntary repetitive motion as the stimulus for pathophysiological changes.

METHODS AND MEASURES

Thirty Sprague-Dawley rats served as controls for 1 or more studies. Ten rats were trained to pull on a bar with 60% maximum force 4 times per minute, 2 h/d, 3 d/wk for 12 weeks. Motor behavior and limb withdrawal threshold force were characterized weekly. Grip strength and median nerve conduction velocity were measured after 12 weeks. Median nerves were examined immunohistochemically for ED1-positive macrophages, collagen, and connective tissue growth factor.

RESULTS

Reach rate and duration of task performance declined over 12 weeks. Grip strength and nerve conduction velocity were significantly lower after 12 weeks than in controls. Limb withdrawal threshold increased between weeks 6 and 12. Median nerves at the level of the wrist showed increases in macrophages, collagen, and connective-tissue growth-factor-positive cells. These effects were seen in both the reach and nonreach limbs.

CONCLUSIONS

This animal model exhibits all the features of human carpal tunnel syndrome, including impaired sensation, motor weakness, and decreased median nerve conduction velocity. It establishes a causal relationship between performance of a repetitive task and development of carpal tunnel syndrome.

The reason for forearm conduction slowing in carpal tunnel syndrome: an electrophysiological follow-up study after surgery

BACKGROUND

The exact cause of decreased forearm median motor conduction velocity (FMMCV) in carpal tunnel syndrome (CTS) is still a subject of controversy. A conduction block or an axonal loss in the large myelinating fibers upon wrist compression, or retrograde axonal atrophy, is suspected.

METHODS

In order to attempt a determination of the cause, 10 patients with clinical symptoms and signs of CTS, confirmed using standard electrodiagnosis and with a slowed FMMCV <50m/s, were included in this study. Serial standard median motor conduction studies were performed at baseline, 1 week, 2 weeks, 4 weeks, 8 weeks, and 12 weeks after endoscopic ligament release. Serial median motor distal latencies (MMDL), compound muscle action potential (CMAP) amplitudes, and FMMCV, were determined and compared.

RESULTS

Significant improvement in MMDL had occurred at the 1-week follow-up examination; however, no such improvement in FMMCV was observed. Furthermore, a significant increase in CMAP amplitude was evidenced beginning 4 weeks after surgery. The results revealed an improvement in median motor conduction, across the wrist segment, that did not parallel the increase in FMMCV, suggesting that a conduction block or axonal loss at wrist compression was not the likely cause of the decreased FMMCV.

CONCLUSIONS

Retrograde axonal atrophy, not selective damage to the large myelinating fibers at the wrist, is the direct cause of decreased FMMCV in CTS.

Forearm mixed nerve conduction velocity: questionable role in the evaluation of retrograde axonal atrophy in carpal tunnel syndrome

The objective of this study was to determine whether forearm mixed nerve conduction velocity (Fmix) reflects the real conduction velocity of forearm motor nerve (Fmot) and forearm sensory nerve (Fsen) fibers passing through the carpal tunnel. Forearm mixed nerve conduction velocity is presumed to be indicative of the conduction velocity of the median nerve over the forearm. Therefore, Fmix is used widely to assess the causes of slowing forearm conduction velocity in carpal tunnel syndrome. However, some authors claim that Fmix comes chiefly from the undamaged fibers in carpal tunnel syndrome, and thus cannot replace Fmot or Fsen in the evaluation of retrograde axonal atrophy. Patients with clinical symptoms and signs of carpal tunnel syndrome confirmed with standard electrodiagnosis were included. Age-matched volunteers served as control subjects. Conduction velocities across the wrist and over the forearm were measured, including those of the wrist sensory (Wsen), wrist motor (Wmot), and wrist mixed nerves (Wmix); and forearm mixed (Fmix), forearm motor (Fmot), and forearm sensory nerves (Fsen). The authors compared and correlated Wsen, Wmot, and Wmix; and Fmix, Fmot, and Fsen respectively. The mean values of Wsen, Wmot, Wmix, Fmix, Fmot, and Fsen of the control subjects less those of corresponding conduction velocity of carpal tunnel syndrome patients were designated Wsen N, Wmot N, Wmix N, Fmix N, Fmot N, and Fsen N respectively and were compared and correlated again. Wrist motor nerve conduction velocity, Wsen, and Wmix were significantly lower in carpal tunnel syndrome patients, and Fmot and Fsen but not Fmix were reduced significantly when compared with control subjects. Mean wrist sensory nerve conduction velocity, Wmot N, and Wmix N; and Fsen N and Fmot N showed good correlation except for Fmix N, suggesting that Fmix reflects the conduction velocity of undamaged fibers in carpal tunnel syndrome. Forearm mixed nerve conduction velocity cannot replace Fmot or Fsen in the assessment of retrograde axonal atrophy in carpal tunnel syndrome. In the disease state, Fmix possibly represents the conduction velocity of the palmar cutaneous branch.

Does direct measurement of forearm mixed nerve conduction velocity reflect actual nerve conduction velocity through the carpal tunnel?

OBJECTIVES

The purpose of this study was to determine whether forearm (wrist-elbow) mixed nerve conduction velocity (W-Emix) represents the actual nerve conduction velocity (CV) of nerve fibers passing through the carpal tunnel.

BACKGROUND

W-Emix is presumed to reflect the actual forearm CV through the carpal tunnel. However, it has been argued that W-Emix chiefly originates from the nerve fibers passing outside the carpal tunnel. Therefore, the direct measurement of W-Emix cannot be used to assess retrograde axonal atrophy in carpal tunnel syndrome (CTS).

SUBJECTS AND METHODS

Thirty patients with clinical signs and symptoms of CTS were recruited and the diagnosis was confirmed with standard electrodiagnosis. Fifty age-matched volunteers served as control. Recording electrodes were placed over the elbow and index finger for mixed nerve and sensory nerve conduction studies, respectively. Stimulation was applied at the palm and wrist for the measurement of mixed nerve wrist-palm CV (W-Pmix), wrist-elbow CV (W-Emix), and elbow-palm CV (E-Pmix). Stimulation was applied at the elbow, wrist, and palm for the measurement of wrist-elbow sensory CV (W-Esen), wrist-palm CV (W-Psen), and elbow-palm CV (E-Psen). Comparisons were made between W-Pmix and W-Psen, W-Emix and W-Esen, and E-Pmix and E-Psen.

RESULTS

Correlations between W-Emix and W-Esen, E-Pmix and E-Psen, and W-Pmix and W-Psen were good in the control. In the patient group, there was a strong positive correlation between W-Pmix and W-Psen, and between E-Pmix and E-Psen. However, W-Esen correlated weakly with W-Emix, suggesting that W-Emix chiefly represents the CV of fibers passing outside the carpal tunnel. Therefore, the direct measurement of W-Emix cannot be used to assess retrograde axonal atrophy. Furthermore, the reduction in W-Psen was more marked than the reduction in W-Esen, implying that a conduction block at the wrist is the least likely cause of proximal slowing in CTS.

CONCLUSIONS

W-Emix does not reflect the actual CV of the nerve fibers passing through the carpal tunnel. In addition, retrograde axonal atrophy appears to be the primary cause of decreased forearm CV in CTS.

Mixed median nerve forearm conduction velocity in the presence of focal compression neuropathy at the wrist versus peripheral neuropathy

OBJECTIVES

To establish normal values for the conduction velocity of the mixed median nerve in the forearm, and to determine the use of mixed median nerve conduction velocity (NCV) studies across the forearm in the differential diagnosis of carpal tunnel syndrome (CTS), peripheral neuropathy, and CTS with peripheral neuropathy.

DESIGN

Criterion standard. Mixed median NCV studies across the forearm were added to routine CTS investigational protocols.

SETTING

University outpatient setting, rural referral base.

PARTICIPANTS

Thirty healthy volunteers and 60 patients referred with symptoms and signs suggestive of CTS and/or peripheral neuropathy.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Motor sensory and mixed median nerve conduction velocity across the forearm.

RESULTS

The mean mixed median NCV across the forearm was 64.5 m/s in healthy subjects and subjects with CTS. The mean mixed NCV in subjects with peripheral neuropathy was 54 m/s, even in the presence of CTS.

CONCLUSION

Mixed median NCV in the forearm added to the standard protocols is helpful in differentiating the diagnosis of CTS from peripheral neuropathy and CTS with peripheral neuropathy.

Pathophysiological tissue changes associated with repetitive movement: a review of the evidence

Work-related musculoskeletal disorders (WMSDs) represent approximately one third of workers' compensation costs in US private industry, yet estimates of acceptable exposure levels for forceful and repetitive tasks are imprecise, in part, due to lack of measures of tissue injury in humans. In this review, the authors discuss the scope of upper-extremity WMSDs, the relationship between repetition rate and forcefulness of reaching tasks and WMSDs, cellular responses to injury in vivo and in vitro, and animal injury models of repetitive, forceful tasks. The authors describe a model using albino rats and present evidence related to tissue injury and inflammation due to a highly repetitive reaching task. A conceptual schematic for WMSD development and suggestions for further research are presented. Animal models can enhance our ability to predict risk and to manage WMSDs in humans because such models permit the direct observation of exposed tissues as well as motor behavior.

The cause of slowed forearm median conduction velocity in carpal tunnel syndrome

OBJECTIVES

Attempting to answer a debate concerning the etiopathogenesis of the decreased forearm median motor conduction velocity (FMMCV), we tried to use proximal stimulation at the wrist, elbow, mid-arm and axillary regions to determine segmental median motor conduction velocity (MMCV). We also correlated the FMMCV with median motor distal latency (MMDL) and compound muscle action potential (CMAP) amplitudes of the abductor pollicis brevis (APB) muscle in order to assess whether the conduction block of large myelinating fibers or retrograde axonal atrophy was the major cause of the decreased FMMCV.

BACKGROUND

The cause of the decreased FMMCV resulting from either the conduction block of the large myelinating fibers at the wrist or distal compression with retrograde axonal atrophy remains an unresolved issue at the moment. Animal models have supported the hypothesis that the retrograde axonal atrophy might also occur in humans. Other authors believe the standard FMMCV is calculated by subtracting the distal latency which may not represent an exact assessment of FMMCV but rather the velocity of small fibers that persist through the carpal tunnel.

SUBJECTS AND METHODS

Patients with the clinical symptoms and signs of carpal tunnel syndrome (CTS) confirmed using standard electrodiagnosis were included. The patients were arbitrarily divided into two groups based on the FMMCV, one with reduced FMMCV (n = 20, FMMCV < 50 m/s) and the other with normal FMMCV (n = 35, FMMCV> or =50 m/s). Age-matched volunteers served as controls. We explored motor conduction proximally at wrist, elbow, mid-arm and axillary stimulation, and recorded at the APB muscles. Based on the latency differences, we calculated the FMMCV, distal arm MMCV (DAMMCV) and proximal arm MMCV (PAMMCV), and compared the conduction velocity (CV) differences of DAMMCV-FMMCV, PAMMCV-FMMCV and PAMMCV-DAMMCV in the two patient groups and the control. Furthermore, we correlated FMMCV with MMDL and CMAP amplitudes of APB muscle because MMDL and CMAP amplitudes might reflect the integrity of the large myelinating fibers.

RESULTS

CMAP amplitudes of APB muscle at wrist stimulation and MMDL were not correlated with FMMCV in either of the two patient groups; however, the CMAP amplitude was markedly decreased and MMDL was significantly prolonged when compared with normal controls. The significant increase of CV gradient of DAMMCV-FMMCV and PAMMCV-FMMCV without an equal increase of CV gradient of PAMMCV-DAMMCV only occurred in the reduced FMMCV patient group, suggesting that the conduction block is not the primary cause. The CV gradient of DAMMCV-FMMCV and PAMMCV-DAMMCV did not show any significant difference between patients with the normal FMMCV and the control group.

CONCLUSION

The retrograde axonal atrophy, not selective damage of the large fibers at the wrist, was the direct cause of the decreased FMMCV.

Heat sensitivity of sensory fibers in carpal tunnel syndrome

Elevations in temperature may produce conduction block in demyelinated neurons. A well-described phenomenon in multiple sclerosis, it has also been reported in some patients with inflammatory demyelinating polyneuropathies. We used carpal tunnel syndrome (CTS) as a model to study the effect of heat on nerves with focal demyelination secondary to chronic compression. Compound motor and sensory responses were measured in 12 CTS patients and 12 normal subjects at 32 degrees C and with heating to 42 degrees C. Changes in relative motor response amplitude and area were similar for both normal subjects and CTS patients. In CTS patients, however, sensory response amplitude and area decreased 34.3% and 48.9%, significantly more than the 25.2% and 39.1% reductions in normal subjects (P=0.021 and P=0.018 respectively). We hypothesize that these reductions in response amplitude are secondary to the occurrence of heat-induced conduction block in demyelinated sensory neurons.

Forearm velocity in carpal tunnel syndrome: when is slow too slow?

OBJECTIVE

To correlate the frequency of superimposed processes (SPs) such as radiculopathies, polyneuropathies, and plexopathies with median motor forearm conduction velocity (MMFCV) in patients with carpal tunnel syndrome (CTS).

DESIGN

All cases of diagnosed CTS were retrospectively analyzed for evidence of SPs.

SETTING

Electrophysiology laboratory of a tertiary care center.

PARTICIPANTS

One hundred fifty-five patients (44 men, 111 women), ages 19 to 94, who were referred for and met electrophysiologic criteria for CTS, both with and without MMFCV slowing.

MAIN OUTCOME MEASURE

The frequency of SPs in patients with no, mild, moderate, and severe MMFCV slowing.

RESULTS

A total of 192 arms from 155 patients were studied. Of 14 arms with mild slowing (MMFCV of 47.0 to 49.9 m/sec), 2 (14%) had an SP. Of 15 arms with moderate slowing (MMFCV of 43.0 to 46.9 m/sec), 7 [corrected] (46%) had an SP. Of 9 arms with severe slowing (MMFCV of < 43.0 m/sec), 4 (44%) had an SP. The frequency of SPs for both the moderate and severe groups was significantly higher than that in patients with a normal MMFCV (p < .01); of 154 arms with a normal MMFCV, only 9 (6%) had an SP.

CONCLUSION

In cases of CTS, the finding of moderate to severe slowing of MMFCV (< 47.0 m/sec) should prompt a careful electrophysiologic investigation to exclude an SP.

Conduction velocity in the forearm segment of the median nerve in patients with impaired conduction through the carpal tunnel

Conduction velocity, in the forearm segment of the median nerve, has been investigated in a group of patients with carpal tunnel syndrome. Motor conduction velocity was reduced below 50 m/s in 18% of the sample. Although a correlation between severity of compression and forearm motor conduction velocity was demonstrated, it was weak (r = 0.51) and slow forearm velocities occurred in some patients who had only a minor abnormality at the carpal tunnel itself. In patients with uncomplicated carpal tunnel syndrome, slow motor conduction in the forearm segment of the median nerve was accompanied by only a small reduction (approx. 5 m/s) in mixed nerve conduction velocity. By contrast, in patients whose abnormality at the carpal tunnel was accompanied by evidence of a more widespread sensorimotor neuropathy, mixed nerve conduction velocity was reduced in parallel with the change in motor conduction velocity.

Morphometric study of myelinated fibers in human cervical spinal cord white matter

STUDY DESIGN

Using human autopsy spinal cord specimens, morphologic measurements of myelinated nerve fibers were performed, focusing on the regions that include the main white matter conduction paths. The hemilateral spinal cord morphology was also measured, and its relation with the component myelinated nerve fibers determined.

OBJECTIVES

To determine the relation between spinal cord transverse area in the normal lower cervical spine, the site most vulnerable to chronic compressive myelopathy, and myelinated nerve fibers.

SUMMARY OF BACKGROUND DATA

Considerable interindividual variation normally is observed in the morphology of the spinal cord transverse area. The influence of this variation on the composition of the white matter myelinated nerve fibers is obscure.

METHODS

The C7 segments from seven cadavers were resected, and from magnified photographs of paraffin-embedded specimens, the hemilateral spinal cord area and funicular area were measured. Nerve fiber morphology was measured using Epon-embedded specimens. Three regions that included the main conduction paths were sampled, and magnified photographs obtained. The nerve fiber transverse morphology was measured using the ellipse conversion method, and the myelinated nerve density and fiber area were determined.

RESULTS

Marked interindividual variations were found in both the hemilateral spinal cord transverse area and funicular area. A positive correlation was noted between the two, with the spinal cord transverse area large in the cases with a large funicular area. For fiber density and area, histograms were constructed that showed characteristic distribution patterns in each region. By dividing each region into two components (i.e., small- and large-diameter fibers), it was found that the interindividual variation in large-diameter fiber density was small, clarifying that the absolute number of large-diameter fibers compared to fiber density is more strongly dependent on the funicular area.

CONCLUSIONS

The absolute number of large-diameter myelinated fibers is smaller in cross-sections of thin as compared to those of thick spinal cord. When elucidating the pathophysiology of compressive myelopathy, it is necessary to study not only the circumstances surrounding the spinal cord, but this kind of factor intrinsic to the spinal cord itself.

Iatrogenic compressive lumbar myelopathy and radiculopathy in adult cattle following injection of an adjuvanted bacterin into loin muscle: histopathology and ultrastructure

Compressive lumbar myelopathy is a recognized iatrogenic complication of injecting water-in-oil vaccines into paravertebral sites of laboratory animals and chickens. Herein, we report the histologic and ultrastructural features of a similar complication in a herd of cattle. Iatrogenic posterior paresis developed over 34 days in 56 of 610 cows (9.2%) following injection of a commercial bacterin 11-34 days earlier into M. longissimus lumborum. The bacterin was composed of inactivated Escherichia coli and Campylobacter fetus ssp. venerealis in a proprietary adjuvant. Tissues were collected for histopathology from 9 affected cattle that died or were euthanized after clinical signs lasting 6-38 days. A range of tissues, including the injection site lesion and lumbar spinal nerve roots, was obtained for ultrastructural examination from a cow with paresis of 31 days duration. There was locally extensive pyogranulomatous myositis with fibrosis and necrosis in right M. longissimus lumborum. Extension of the lesion into the vertebral canal via spinal nerve foramina resulted in focal pyogranulomatous inflammation in epidural fat and in adjacent dura mater. There was axonal degeneration in dorsal, lateral, and ventral columns and chromatolysis of spinal motor neurons in lumbar spinal cord, secondary to compression. A distinctive histologic and ultrastructural feature of pyogranulomata was the presence of osmiophilic material at the center of inflammatory foci, surrounded by macrophages and giant cells that contained intracytoplasmic lipid droplets. Ultrastructural examination of entrapped spinal nerves revealed axonal degeneration and loss of myelinated and unmyelinated fibers, segmental demyelination with remyelination, axonal spheroid formation, and early axonal regeneration.(ABSTRACT TRUNCATED AT 250 WORDS)

Does forearm mixed nerve conduction velocity reflect retrograde changes in carpal tunnel syndrome?

The mixed nerve conduction velocity of the median nerve in the forearm diverged from the motor and sensory nerve conduction velocities and correlated poorly with the severity of carpal tunnel syndrome (CTS) in 61 hands. In contrast, the motor and sensory nerve conduction velocities in the forearm correlated well with CTS severity. The mixed nerve conduction velocity in the forearm is probably determined by nonlesioned fibers such as those from the cutaneous palmar branch of the median nerve. The motor and sensory, but not the mixed nerve conduction velocities in the forearm may be used to estimate possible retrograde impairment in CTS.

Retrograde effects of digital nerve severance on somatosensory evoked potentials in man

To determine if retrograde conduction changes might occur long after injury of the most distal peripheral nerves, short-latency somatosensory evoked potentials (SEPs) to median or ulnar nerve stimulation at the wrist were studied in 10 subjects who had sustained traumatic digit amputation 4 months to 15 years previously. SEPs were recorded from Erb's point (N9), the cervical region (N13), and the contralateral scalp hand area (N20). While N9 latency was slightly delayed or not affected, the amplitude was either markedly reduced or undetectable. For N13 and N20 components, latency prolongation and amplitude reduction were mild to moderate, but the central conduction time (N13-N20) remained normal. The present data indicate that even the most distal nerve injury may have profound long-term retrograde effects on parental nerve function which are presumed mainly due to an axonopathy.

Proximal slowing in carpal tunnel syndrome resulting from either conduction block or retrograde degeneration

In the carpal tunnel syndrome (CTS), decreased conduction velocity (CV) of the median nerve in the forearm segment has been ascribed to an electrodiagnostic artefact rather than pathophysiological changes. Standard CV of the forearm segment is calculated by subtracting the distal latency, which may not represent an exact assessment of CV in the proximal median nerve. A new technique modified from the method of Stoehr et al. and Pease et al. can exactly measure CV over the forearm. Using this new technique, the forearm nerve action potentials (FNAP) amplitude and forearm nerve conduction velocity (FNCV) proximal to the wrist can be directly determined. Normal subjects and patients with CTS were studied by both the standard and the new FNAP methods. Patients were divided into subgroups according to the severity derived from standard electro-diagnostic findings. By comparing the normal control and patient subgroups, the results show that there was a significant decrease in FNAP amplitudes proportional to severity, but FNCV was reduced to a lesser extent. In addition, the standard forearm median motor CV (MMCV) correlated well with severity, but the reduced MMCV did not correlate with the decreased FNCV. These findings suggest that retrograde degeneration of the median nerve does exist in CTS; however, retrograde degeneration contributes little to the reduced forearm MMCV which substantially results from the block of faster conduction fibres at the wrist. Therefore, technique artefact plays a major role in causing the proximal slowing in the standard electrodiagnosis.

Carpal tunnel syndrome: a clinical electrophysiological study of 84 cases

A retrospective study of 84 patients with carpal tunnel syndrome (CTS), for a total of 118 hands, was performed in order to check clinical aspects of the disease including age of onset, sex, side affected, other associated pathological conditions, and to assess the existence of correlation between the clinical picture and electrophysiological parameters. All patients were subjected to careful clinical observation and electromyographic and electroneurographic examinations. Our study confirms that the female sex is by far predominant, the most interesting ages being the 5th and 6th decades of life and the right side is more affected than the left. None of the patients had a family history of CTS. The sensory pathology is far more frequent than the motor one and the percentage of hands with sensory and motor deficit increases with the duration of the disease. As far as the electrophysiological data is concerned, the most important and also the earliest alterations fundamentally concern the distal motor latency and distal sensory conduction velocity of the median nerve and the amplitude of its sensory action potential (SAP). This study leads us to point out a significant correlation in CTS between electrophysiological (distal motor latency and distal sensory conduction velocity of the median nerve, amplitude of its SAP) and clinical parameters (symptomatology and duration of the disease).

Correlation studies of velocity, amplitude, and duration in median nerves

Nerve conduction velocity is the parameter most often attended to when performing nerve conduction studies, but amplitude and duration of the nerve potentials should also provide important information about the status of the nerve examined. This study compared the results of amplitude and duration measurement to nerve conduction velocity to determine whether or not the various parameters correlated. Using standard techniques, median nerve motor and sensory conduction studies were performed on 390 unselected patients. The results were analyzed and correlation statistics calculated between the parameters of velocity, duration, and amplitude. Amplitude and duration of evoked potential correlated relatively poorly with conduction velocity (r2 = 0.26). Sensory and motor fibers were often affected differently in cases with probable carpal tunnel syndrome (CTS). Proximal motor conduction velocity correlated best with distal evoked potential amplitude (r2 = 0.27) in the CTS cases. The use of residual latency appeared to add little helpful diagnostic information. It was concluded that different parameters measure different physiologic processes that are to a considerable degree independent of each other.

Prediction of Outcome of Decompression for Carpal Tunnel Syndrome

45 patients (55 hands) with carpal tunnel syndrome treated surgically have been studie Painful nocturnal paraesthesiae occurred in patients with short histories and was a good prognostic feature. Electromyography proved of value in assessing motor lesions and the degree of the process. The first sign of muscle involvement was fibrillation potential. In longer histories an increased amount of polyphasic potentials and reduced voluntary pattern was seen. The reduced pattern is reversible in cases of short duration and the absence of muscle wasting. In cases with marked alteration and signs of chronic muscle degeneration, the prognosis for pain is good, but not so for the neurological deficit. The nerve conduction velocity improve quickly after decompression of the median nerve in accordance with the complaints of the patient Electrophysiological methods proved their value in staging and follow-up.

Subclinical entrapment neuropathy of the equine suprascapular nerve

The suprascapular nerve from 14 horses, which had no clinical evidence of spinatus muscle atrophy, were obtained to determine whether the nerve was sub-clinically compressed at the scapular edge. The nerves were divided into three portions, proximal and distal to the scapular edge and as it reflected around it. In nine horses there was evidence of a chronic neuropathy which varied in severity and which was most severe at the site of reflection, where the nerve appeared constricted by a tendinous band. At this site the predominant change was that of chronic demyelination and remyelination, with many scattered thinly myelinated fibres and occasionally profuse onion bulb formation. There were also occasional regenerating clusters, which were the only abnormalities seen in the distal nerve. Renaut bodies appeared to be more common and larger in nerves with chronic focal neuropathy. Teased fibres confirmed the chronic myelin sheath changes, and the presence of many paranodal swellings suggested a possible chronic compressive aetiology. This is the first reported spontaneous entrapment neuropathy in the domestic animals.

Effects of acute nerve compression on conduction of impulse trains of increasing frequency

The acute effect of localized nerve compression has been detected electrophysiologically in isolated rat tail nerve by utilizing a special stimulus pattern, a STIF (Stimulus Train of Increasing Frequency), which shows the highest frequency that the most sensitive axons in a compound potential can transmit through the compressed region. The same method also detected recovery after release of compression. Overlap of waveforms at high frequencies of stimulation required special techniques to permit unequivocal measurements. The best endpoint at which to detect the acute nerve compression in these experiments was found to be that frequency at which only a few fibers were blocked. The method was also effective when part of the nerve was completely blocked by the compression, and was more sensitive than measure of change in latency of a single response.

Demyelination following diphtheria toxin in the presence of axonal atrophy

In 23 guinea-pigs a constricting ligature was placed on the tibial nerve in the thigh on one side, in order to produce axonal atrophy in the distal part of the nerve. Either before or after ligature, 10 of the guinea-pigs received subcutaneous diphtheria toxin into the abdominal wall, in a dose insufficient to cause generalised paralysis or reduced motor conduction velocity (MCV). In 7 of the 10 animals, MCV distal to the ligature fell below the range seen after ligature alone. In animals which had received toxin histological studies revealed paranodal and segmental demyelination in the distal tibial nerve, which was more extensive on the side of the ligature than in the opposite leg. Occasional paranodal but no segmental demyelination was seen distal to ligature alone. These results indicate that a small dose of systemic diphtheria toxin is more likely to produce peripheral nerve demyelination if an axonal abnormality is also present.

Renaut body distribution at sites of human peripheral nerve entrapment

In an autopsy study of the pathology of chronic subclinical nerve entrapment Renaut bodies showed a strong predilection for sites of nerve entrapment. They were present at these sites in 43 of 74 peripheral nerves but in none of the control sections of the same nerves. Renaut bodies were most frequently encountered in the median nerve at the wrist and in the lateral femoral cutaneous nerve at the inguinal ligament but were rarely seen in sections of the common peroneal nerve at the neck of the fibula. Renaut bodies were closely associated with thickened subperineurial capillaries, and, in successive transverse sections, they terminated in a fibrous mass of these thickened vessels. In several nerves Renaut bodies showed a similar orientation within adjacent fascicles, suggesting that mechanical factors were related to their pathogenesis; despite this finding there was no relationship between their numbers at entrapment sites and the presence of pathological changes in myelinated nerve fibres at the same level. These findings suggest that while mechanical factors are important in the pathogenesis of Renaut bodies there is no evidence to support the theory that these structures protect nerve fibres from mechanical stress.

Pathologic significance of Meniere's symptom complex. A histopathologic and electron microscopic study

Histologic and ultrastructural findings in the temporal bones of a patient clinically diagnosed as having unilateral Meniere's disease are presented. The patient underwent two endolymphatic subarachnoid shunt operations that failed to relieve symptoms and a middle fossa vestibular nerve section that completely relieved episodic vertigo and stabilized hearing in the ear operated upon. Histopathologic examination of the temporal bones showed no endolymphatic hydrops in either ear. The maculae and cristae on the side operated upon showed severe degenerative changes attributed to vestibular neurectomy. The cochleograms of the operated and contralateral ears showed degeneration of the sensorineural structures in the basal two turns of the cochlea. No apparent cause for the fluctuant hearing loss was found in the cochlea or the cochlear nerve of the involved ear. Light and electron microscopic studies of the vestibular nerve excised at the time of vestibular neurectomy showed that most of the nerve fibers and ganglion cells were essentially normal. Collagen tissue deposition was increased in some areas of the endoneurial space. Most myelinated nerve fibers in these areas had degenerated. Although these changes may be partly due to artifacts and partly due to aging, they probably are the result of a pathologic process affecting the vestibular nerve. These findings suggest that a revised approach to the etiology, pathogenesis, and treatment of Meniere's symptom complex is indicated.

Congenital arteriovenous fistula producing carpal tunnel syndrome

A case of carpal tunnel syndrome resulting from congenital arteriovenous fistula is described.

Subclinical entrapment of the lateral femoral cutaneous nerve: an autopsy study

Five out of 12 lateral femoral cutaneous nerves, removed at routine autopsies, showed pathologic changes in myelinated nerve fibers in the vicinity of the inguinal ligament. These changes included both local demyelination and Wallerian degeneration, particularly affecting the fibers with the largest diameters. The presence of polarized internodal swellings on single nerve fibers from two specimens suggested that mechanical factors were involved in pathogenesis. Endoneurial vascular thickening confined to the region of the inguinal ligament was also seen and may be implicated in the production of some of the symptoms of meralgia paresthetica (MP).

Retrograde changes of nerve fibers with the carpal tunnel syndrome. An electroneurographic investigation

In the CTS the motor nerve conduction velocity proximal to the wrist is reduced in proportion to the degree of severity of the nerve lesion. Furthermore the evoked nerve action potential is significantly reduced when recordings are made from the median nerve at the elbow and when the compound nerve is stimulated proximal to the lesion at the wrist. The extent of the retrograde changes correlates with the degree of severity and duration of nerve compression. Measurement of the evoked nerve action potential in the proximal nerve segment enables us to estimate the extent of the retrograde nerve fiber degeneration and therefore might be important for prognosis.

Axonal dwindling in early experimental diabetes. II. A study of isolated nerve fibres

In a morphometric study of isolated fibres of the common peroneal nerve in short-term diabetic rats reduced fibre calibre was observed. No segmental demyelination or remyelination was found, but the nodes of Ranvier were slightly widened and paronodal bulbi were swollen relative to fibre calibre. It is suggested that axonal dwindling is the primary event in experimental diabetes. The reduction of the myelin sheath may be a consequence of the abnormal nerve cell offshoot. The results obtained suggest that streptozotocin diabetes in the rat is a useful model for the elucidation of diabetic neuropathy.

Morton's metatarsalgia. Light and electron microscopic observations and their relation to entrapment neuropathies

The dissected plantar nerves of 105 patients with clinical symptoms of Morton's disease were examined under light and electron microscopy. Of the 105 cases, 75 showed characteristic neuronal lesions; in the others different pathologic substrates responsible for the clinical symptoms could be demonstrated. The nervous lesions are characterized by: 1. Thickening of the walls of the endoneurial vessels produced by multiple layers of basement membranes. 2. Edema and sclerosis of the endoneurium. In the electron microscope the endoneurium was filled by deposits of fibrils with a tubular substructure and a diameter of 100-110 A. 3. Thickening of the perineurium. 4. Degeneration of the nerve fibers without signs of wallerian degeneration or obvious reactive Schwann's cell hyperplasia. The possible pathogenetic mechanisms of Morton's disease and some clinical problems are discussed.

The nerve lesion in the carpal tunnel syndrome

The relative roles of pressure deformation and ischaemia in the production of compression nerve lesions remain a controversial issue. This paper concerns the genesis of the structural changes which follow compression of the median nerve in the carpal tunnel. The initial lesion is an intrafunicular anoxia caused by obstruction to the venous return from the funiculi as the result of increased pressure in the tunnel. This leads to intrafunicular oedema and an increase in intrafunicular pressure which imperil and finally destroy nerve fibres by impairing their blood supply and by compression. The final outcome is the fibrous tissue replacement of the contents of the funiculi.

Sub-clinical entrapment neuropathy in man

Twelve median and 12 ulnar nerves were obtained at routine autopsies from patients without known disease of the peripheral nervous system. Enlargement of cross-sectional area due to an increase in connective tissue elements was commonly present in the ulnar nerve at the elbow and in the median nerve under the flexor retinaculum. Renaut bodies were also prominent at these two sites. The connective tissue changes did not appear to be related to the presence or absence of nerve fibre damage. When nerve fibres were teased apart and examined individually, localised changes were found at the elbow in 5 ulnar nerves and under the flexor retinaculum in 5 median nerves. The changes were mild and transverse sections at the same levels showed few abnormalities. However, the changes were similar in character to those described previously in experimental animals with entrapment syndromes. They are therefore considered to be valid evidence of sub-clinical entrapment in apparently unaffected human subjects.

Electrophysiological study after surgical repair of sectioned human peripheral nerves

Clinical and electrophysiological assessment of recovery of function are reported on 20 patients with median or ulnar nerve sections up to 53 months after surgical repair. Maximum improvement of sensory function was apparent by both methods of assessment at 15 months after suture, and thereafter conduction velocities in sensory fibres averaged 80% of normal in median nerves and 70% of normal in ulnar nerves. Similarly, the mean amplitude of the sensory action potential at the wrist remained depressed at 15% of control values. The clinical recovery of motor function pursued a similar time course with, however, some evidence to indicate a continuing improvement in the neurophysiological maturation of the motor nerve fibres up to 47 months after repair. The results are discussed in relation to previous electrophysiological studies on animals.

Ulnar nerve lesions associated with the carpal tunnel syndrome

Electrophysiological studies were performed on median and ulnar nerves in 234 cases of carpal tunnel syndrome. Abnormalities of the ulnar nerve sensory action potential were found in 39·3% of cases. The amplitude of the ulnar nerve sensory action potential was related to the amplitude of the median nerve sensory action potential, and to the median nerve motor conduction velocity in the forearm. The findings suggest that in a significant proportion of patients with carpal tunnel syndrome, a more generalized subclinical neuropathy may be present.