Correlation between quantitative EMG and muscle MRI in patients with axonal neuropathy

Lower motoneuron dysfunction impacts spontaneous motor recovery in acute cervical spinal cord injury

Paresis after spinal cord injury is caused by damage to upper and lower motoneurons and may differentially impact neurological recovery. This prospective monocentric longitudinal observational study investigated the extent and severity of lower motoneuron dysfunction and its impact on upper extremity motor recovery after acute cervical spinal cord injury. Pathological spontaneous activity at rest and/or increased discharge rates of motor unit action potentials recorded by needle electromyography (EMG) were taken as parameters for lower motoneuron dysfunction and its relation to the extent of myelopathy in the first available spine MRI was determined. Motor recovery was assessed by standardized neurological examination within the first 4 weeks (acute stage) and up to 1 year (chronic stage) after injury. Eighty-five muscles of 17 individuals with cervical spinal cord injury (neurological level of injury from C1 to C7) and a median age of 54 (28-59) were examined. The results showed that muscles with signs of lower motoneuron dysfunction peaked at the lesion center (Χ²[2,n=85]=6.6, p=0.04) and that the severity of lower motoneuron dysfunction correlated with T2-weighted hyperintense MRI signal changes in routine spine MRI at the lesion site (spearman ρ=0.31, p=0.01). Muscles exhibiting signs of lower motoneuron dysfunction, as indicated by pathological spontaneous activity at rest and/or increased discharge rates of motor unit action potentials, were associated with more severe paresis in both the acute and chronic stages after spinal cord injury (spearman ρ acute=-0.22, p=0.04 and chronic=-0.31, p=0.004). Moreover, the severity of lower motoneuron dysfunction in the acute stage was also associated with a greater degree of paresis (spearman ρ acute=-0.24, p=0.03 and chronic=-0.35, p=0.001). While both muscles with and without signs of lower motoneuron dysfunction were capable of regaining strength over time, those without lower motoneuron dysfunctions had a higher potential to reach full strength. Muscles with signs of lower motoneuron dysfunction in the acute stage displayed increased amplitudes of motor unit action potentials with chronic-stage needle EMG, indicating reinnervation through peripheral collateral sprouting as compensatory mechanism (Χ²[1,n=72]=4.3, p=0.04). Thus, lower motoneuron dysfunction represents a relevant factor contributing to motor impairment and recovery in acute cervical spinal cord injury. Defined recovery mechanisms (peripheral reinnervation) may at least partially underlie spontaneous recovery in respective muscles. Therefore, assessment of lower motoneuron dysfunction could help refine prediction of motor recovery following spinal cord injury.

Asymmetric recurrent laryngeal nerve conduction velocities and dorsal cricoarytenoid muscle electromyographic characteristics in clinically normal horses

The dorsal cricoarytenoid (DCA) muscles, are a fundamental component of the athletic horse's respiratory system: as the sole abductors of the airways, they maintain the size of the rima glottis which is essential for enabling maximal air intake during intense exercise. Dysfunction of the DCA muscle leads to arytenoid collapse during exercise, resulting in poor performance. An electrodiagnostic study including electromyography of the dorsal cricoarytenoid muscles and conduction velocity testing of the innervating recurrent laryngeal nerves (RLn) was conducted in horses with normal laryngeal function. We detected reduced nerve conduction velocity of the left RLn, compared to the right, and pathologic spontaneous activity (PSA) of myoelectrical activity within the left DCA muscle in half of this horse population and the horses with the slowest nerve conduction velocities. The findings in this group of horses are consistent with left sided demyelination and axonal loss, consistent with Recurrent Laryngeal Neuropathy (RLN), a highly prevalent degenerative disorder of the RLn in horses that predominantly affects the left side. The detection of electromyographic changes compatible with RLN in clinically unaffected horses is consistent with previous studies that identified "subclinical" subjects, presenting normal laryngeal function despite neuropathologic changes within nerve and muscle confirmed histologically.

Muscle echogenicity ratio can indicate severity of carpal tunnel syndrome

INTRODUCTION

The purpose of this study was to investigate the usefulness of the echogenicity (EI) ratio of the thenar to hypothenar muscle measured using ultrasonography in assessing the severity of carpal tunnel syndrome (CTS).

METHODS

Fifty-nine hands of 30 patients electrodiagnostically confirmed as having CTS were classified into 3 subgroups (mild, moderate, and severe). The EI of the thenar and hypothenar muscles was measured with ultrasonography, and the EI ratio was calculated in the patients and 13 normal participants (26 hands).

RESULTS

The average EI ratio was higher in the CTS group than in the control group. We also found a positive correlation between the severity of CTS and a high EI ratio measured with ultrasonography.

DISCUSSION

The EI ratio of the thenar to hypothenar muscle is a useful parameter that can indicate the severity of CTS. Muscle Nerve 58: 304-306, 2018.

Imaging of the peripheral nervous system

This chapter summarizes progress in the evaluation of peripheral nerve (PN) lesions and disorders by imaging techniques encompassing magnetic resonance imaging (MRI) and nerve ultrasound (US). Due to the radiation exposure and limited sensitivity in soft tissue contrast, computed-tomography (CT) plays no significant role in the diagnostic work-up of PN disorders. MRI and US are complementary techniques for the evaluation of peripheral nerves, each having particular advantages and disadvantages. Nerve injury induces intrinsic MRI signal alterations on T2-weighted sequences in degenerating or demyelinating nerve segments as well as in corresponding muscle groups exhibiting denervation which can be exploited diagnostically. Nerve US is based on changes in the nerve echotexture due to tumor formation or focal enlargement caused by entrapment or inflammation. Both MRI and US provide morphological information on the precise site and extent of nerve injury. While US has the advantage of easy accessibility, providing images with superior spatial resolution at low cost, MRI shows better soft tissue contrast and better image quality for deep-lying nerve structures since imaging is not hindered by bone. Recent advances have remarkably increased spatial resolution of both MRI and US making imaging indispensible for the elucidation of causes of nerve compression, peripheral nerve tumors, and focal inflammatory conditions. Both MRI and US further guide neurosurgical exploration and can simplify treatment. Importantly, imaging can reveal treatable conditions even in the absence of gross electrophysiological alterations, illustrating its increasing role in clinical practice. In experimental settings, novel molecular and cellular MRI contrast agents allow in-vivo assessment of nerve regeneration as well as monitoring of neuroinflammation. Depending on further clinical development, contrast-enhanced MRI has the potential to follow cellular responses over time in vivo and to overcome the current limitations of histological assessment of nerve afflictions. Further advances in contrast-enhanced US has the potential for developing into a tool for the assessment of nerve blood perfusion, paving the way for better assessments of ischemic neuropathies.

Diffusion-weighted MRI, dynamic susceptibility contrast MRI and ultrasound perfusion quantification of denervated muscle in rabbits

OBJECTIVE

The purpose of this study was to assess denervated muscle perfusion using dynamic susceptibility contrast MRI (DSCMRI) and contrast-enhanced ultrasound (CEUS), and to measure denervated muscle apparent diffusion coefficient (ADC) on b1000 diffusion-weighted MRI (DWMRI) at 3 T in order to clarify whether muscle denervation leads to an increase in the extracellular extravascular space, or an increase in blood flow-or both.

MATERIALS AND METHODS

Axotomy of the right sciatic nerve of six white rabbits was performed at day 0. At day 9, hind limb muscles MRI and CEUS were performed to assess the consequences of denervation and both semimembranosus muscles of each rabbit were explanted for histological studies. Signal intensity on T2- and T1-weighted MRI, ADC on DWMRI, maximum signal drop (MSD) on DSCMRI and the area under the curve (AUC) on CEUS were measured over circular regions of interest (ROI), in both semimembranosus muscles. Non-parametric Wilcoxon matched-pairs tests were used to assess the mean differences between denervated and normal muscles.

RESULTS

T2 fat-saturated (FS) MRI studies showed a strong signal in the right semimembranosus muscles compared with the left side, and gadolinium enhancement was observed on T1 FS MRI. Denervated muscles show a significant increase in ADC on DWMRI (p < 0.01) and a significant signal enhancement on DSCMR imaging (p < 0.05) and on first-pass CEUS (p < 0.05).

CONCLUSION

The results of this study--based on perfusion- and diffusion-weighted images--suggest that, after denervation, both increased blood flow through muscle tissue and expansion of the extracellular water volume are present.

Magnetic resonance imaging of the peripheral nervous system

The diagnostic work up of patients with peripheral neuropathy largely depends on clinical and electrophysiological investigations. In contrast to disorders of the CNS, magnetic resonance imaging (MRI) has not been widely used as a diagnostic tool in the PNS except for detection of nerve compressing mass lesions. Normal nerves appear isointense to the surrounding tissue on T1- and T2-weighted (w) MRIs, but upon injury the nerves become hyperintense and thus visible on T2-w MRI. These signal alterations can be exploited to diagnose nerve damage in vivo and to follow regeneration. In patients with peripheral nerve disorders, MRI has been especially useful in detecting focal intrinsic and extrinsic nerve lesions and may reveal treatable conditions even in the absence of gross electrophysiological alterations. This clinical review provides practical guidelines on the performance of nerve imaging by MRI and will focus on focal lesions exemplified by case presentations.

Diffusion-weighted MRI of denervated muscle: a clinical and experimental study

OBJECTIVE

The aim of this study was to investigate skeletal muscle denervation using diffusion-weighted magnetic resonance imaging (DWMRI).

MATERIALS AND METHODS

Sciatic nerve axotomy was performed in a group of nine New Zealand White rabbits, and electromyographic (EMG), pathological, and DWMRI studies were conducted on ipsilateral hamstring muscles 1 and 8 days after axotomy. In addition, DWMRI studies were carried out on leg muscles of ten patients with acute and subacute lumbosacral radiculopathy.

RESULTS

High intensity signals on short tau inversion recovery (STIR) magnetic resonance imaging and an increased apparent diffusion coefficient (ADC) were observed in denervated muscles of the animals 1 and 8 days after axotomy as well as in denervated muscles of the patients with radiculopathy. In the clinical study, ADC was 1.26 +/- 0.18 x 10(-9) m(2)/s in normal muscle and increased to 1.56 +/- 0.23 x 10(-9) m(2)/s in denervated muscles (p = 0.0016). In animals, EMG and muscle pathological studies were normal 1 day after axotomy, and the muscles demonstrated spontaneous activity on EMG and neurogenic atrophy on histological studies 7 days later.

CONCLUSION

This DWMRI study demonstrates that enlargement of extracellular fluid space in muscle denervation is an early phenomenon occurring several days before the appearance of EMG and histological abnormalities.

Winged scapula caused by a dorsal scapular nerve lesion: a case report

Dorsal scapular nerve lesions are quite rare. A case of a 51-year-old man who had right shoulder pain, weakness of right arm elevation, and prominence of right scapula for 6 months is presented. The condition had been abruptly developed after lifting a heavy box overhead on which he felt a sharp pain in the right shoulder. On clinical examination, there was a prominence of the lower medial border and inferior angle of the right scapula compared with the left. In addition, the right scapula was located more lateral. Magnetic resonance imaging of the thorax revealed the presence of a thinner rhomboid major muscle with a pathologic signal compared with the other side. Needle electromyography of the right rhomboid muscle revealed a long duration, polyphasic motor unit potential with reinnervation potentials, and spontaneous activity. According to these findings, the patient was diagnosed as having a winged scapula because of dorsal scapular nerve lesion.

Technology insight: visualizing peripheral nerve injury using MRI

Currently, the evaluation of peripheral nerve disorders depends on clinical examination, supplemented by electrophysiological studies. These approaches provide general information on the distribution and classification of nerve lesions-for example, axonal versus demyelinative-but nerve biopsies are still required to obtain morphological and pathophysiological details. In this article, we review recent progress in the imaging of peripheral nerve injury by magnetic resonance (MR) neurography. Axonal nerve injury leads to Wallerian degeneration, resulting in a hyperintense nerve signal on T2-weighted MR images of the distal nerve segment. This signal is lost following successful regeneration. Concomitant denervation-induced signal alterations in muscles can further help us to determine whether nerve trunks or roots are affected. These signal changes are caused by various combinations of nonspecific tissue alterations, however, and are not related to particular pathoanatomical findings, such as inflammation, demyelination or axonal injury. New experimental MR contrast agents, such as gadofluorine M and superparamagnetic iron oxide particles, allow visualization of the dynamics of peripheral nerve injury and repair. Further clinical development of these MR contrast agents should allow these functional aspects of nerve injury and repair to be assessed in humans, thereby aiding the differential diagnosis of peripheral nerve disorders.

Peripheral Neuropathies of the Median, Radial, and Ulnar Nerves: MR Imaging Features

The median, radial, and ulnar nerves of the upper limbs may be affected by various peripheral neuropathies, each of which may be categorized according to its cause, as either an entrapment or a nonentrapment neuropathy. Entrapment neuropathies, also referred to as nerve compression syndromes, include the supracondylar process syndrome, pronator syndrome, anterior interosseous nerve syndrome, carpal tunnel syndrome, posterior interosseous nerve syndrome, cubital tunnel syndrome, and Guyon canal syndrome. Nonentrapment neuropathies include traumatic nerve injuries, infectious and inflammatory conditions, polyneuropathies, and mass lesions at anatomic locations where entrapment syndromes typically do not occur. Although clinical examination and electrophysiologic testing are the cornerstone of the diagnostic work-up, in certain cases magnetic resonance (MR) imaging may provide key information about the exact anatomic location of a lesion or may help narrow the differential diagnosis. In patients with a diagnosis of peripheral neuropathy, MR imaging may help establish the cause of the condition and provide information crucial for conservative management or surgical planning. In addition, knowledge of the normal anatomy and of the possible causes, typical clinical findings, and MR imaging features of peripheral neuropathies that affect the median, radial, and ulnar nerves allows greater confidence in the diagnosis.

MRI morphology of the levator ani muscle, endopelvic fascia, and urethra in women with stress urinary incontinence

OBJECTIVE

To evaluate pathomorphologic changes of the levator ani muscle, endopelvic fascia, and urethra in women with stress urinary incontinence (SUI) by MRI.

STUDY DESIGN

Fifty-four women with SUI were examined by MRI (1.5T): body phased-array coil, axial and coronal proton-density-weighted sequences.

RESULTS

The urethral sphincter muscle showed a reduced thickness of its posterior portion (37%), an omega shape (13%) or higher signal intensity (50%); its abnormal configuration was associated with an increased signal intensity in 70% (p=0.001). The levator ani muscle comprised an unilateral loss of substance in 30%, a higher signal intensity in 28%, and altered origin in 19%. Central defects of the endopelvic fascia were present in 39% (n=21), lateral defects in 46%. There was a significant association between loss of the symphyseal concavity of the anterior vaginal wall and lateral fascial defects (p=0.001) and levator ani changes (p=0.016).

CONCLUSION

MRI yields findings supporting current theories on the pathogenesis of SUI.

Imaging of peripheral nerve lesions

PURPOSE OF REVIEW

Clinical investigations of peripheral nerve lesions routinely involve nerve conduction studies and electromyography. Imaging studies are often used to exclude focal mass lesions or external compression and to visualize muscle atrophy. More recently, it has been recognized that magnetic resonance imaging can identify changes in peripheral nerves and secondary neurogenic alterations in skeletal muscle, which may significantly enhance its use in the differential diagnosis of peripheral nerve disease.

RECENT FINDINGS

Acute axonal nerve lesions cause a hyperintense signal on T2-weighted images at and distal to the lesion site, which correlates with Wallerian degeneration and nerve oedema. Superparamagnetic iron oxide particles provide an exciting new tool to detect the invasion of macrophages into the degenerating nerve distal to an axonal lesion. Prolongation of the T2 relaxation time and gadolinium enhancement of denervated muscle develop in parallel to the development of spontaneous activity on electromyography, and are probably the consequence of capillary enlargement and increased muscular blood volume.

SUMMARY

Magnetic resonance imaging supplements the differential diagnosis of peripheral nerve disease. An advantage over clinical neurophysiological investigations is that it is operator independent and painless. It can identify axonal damage and may thus help to identify a lesion site precisely, where fractionated nerve conduction studies are not applicable. Novel contrast media may potentially be used to detect pathophysiologically relevant mechanisms such as infiltration of the nerve by macrophages. Magnetic resonance imaging also has the advantage of providing a lasting detailed topographical picture of regional variations and avoids localization errors of muscles in electromyography.

MR neurography and muscle MR imaging for image diagnosis of disorders affecting the peripheral nerves and musculature

Recent advances in the technology of MR imaging are beginning to transform the fundamental methodology of diagnostic evaluations in neuromuscular disorders. When properly implemented, MR neurography is capable of providing high-quality information about nerve compression, nerve inflammation, nerve trauma, systemic neuropathies, nerve tumors, and recovery of nerve from pathologic states. Muscle MR imaging can identify denervation on a precise anatomic basis, document the progression of various conditions causing myopathy and myositis; and even provide insight into abnormal patterns of muscle activation. There is an essential role for the neurologist as well as for the specialist radiologist that requires a high level of familiarity of the various new types of image findings in this steadily advancing field.

Muscle magnetic resonance imaging of denervation and reinnervation: correlation with electrophysiology and histology

A signal increase in denervated muscle on magnetic resonance imaging (MRI) has been described in several clinical and experimental studies. Here, we studied the time course of T2-relaxation time changes in denervation and subsequent reinnervation in a rat model and correlated the findings with electrophysiology and quantitative histology. A prolongation of the T2 relaxation time in muscles was present 48 h after denervation, which was paralleled by spontaneous activity on electromyography (EMG). Histologically, there was a marked enlargement of the capillaries at that time point, indicating increased blood volume. The relaxation time changes peaked 3 weeks after beginning of nerve regeneration identified by EMG. Subsequently, the T2 prolongation normalized until 10 weeks after beginning of regeneration which was associated with a histological regression of the capillary enlargement. MRI closely mirrors the electrophysiological changes following denervation and reinnervation and may thus be used as adjunct to electrophysiology. The pathophysiological basis for the MR relaxation time changes is predominantly the enlargement of the capillary bed.

Reliability of quantitative motor unit action potential parameters

We evaluated the test-retest reliability (reproducibility) of motor unit action potential (MUAP) parameters in multi-MUAP analysis over time. Reproducibility studies are not available for needle quantitative electromyography (QEMG) performed by the same examiner. Fourteen consecutive individuals (10 men and 4 women) had repeat QEMG at 3 hours after the first examination, and seven (5 men and 2 women) had a repeat QEMG after 4-10 days. The intraclass correlation coefficient (ICC) was 87-97% with same-day testing and 52-81% with different-day testing. Size index and firing rate were the most reproducible, suggesting use in follow-up multi-MUAP studies.