The ability to view individual myofibers is possible with many histological techniques, but not yet with standard in vivo imaging. Optical coherence tomography (OCT) is an emerging technology that can generate high resolution 1–10 μm cross-sectional imaging of tissue in vivo and in real time.
We used OCT to determine architectural differences of tibialis anterior muscles in situ from healthy mice (wild-type [WT], n = 4) and dystrophic mice (mdx, n = 4). After diffusion tensor imaging (DTI) and OCT, muscles were harvested, snap-frozen, and sectioned for staining with wheat germ agglutinin.
DTI suggested differences in pennation and OCT was used to confirm this supposition. OCT indicated a shorter intramuscular tendon (WT/mdx ratio of 1.2) and an 18% higher degree of pennation in mdx. Staining confirmed these architectural changes.
Architectural changes in mdx muscles, which could contribute to reduction of force, are detectable with OCT.
mdx; mouse imaging; muscular dystrophy; skeletal muscle; small animal imaging
Duchenne muscular dystrophy (DMD) is a devastating muscle disorder that affects 1 in 3500 boys. Despite years of research and considerable progress in understanding the molecular mechanism of the disease and advancement of therapeutic approaches, there is no cure for DMD. The current treatment options are limited to physiotherapy and corticosteroids, and although they provide a substantial improvement in affected children, they only slow the course of the disorder. On a more optimistic note, the most recent approaches either significantly alleviate or eliminate muscular dystrophy in murine and canine models of DMD and importantly, many of them are being tested in early phase human clinical trials. This review summarizes advancements that have been made in viral and non-viral gene therapy as well as stem cell therapy for DMD with a focus on the replacement and repair of the affected dystrophin gene.
Duchenne muscular dystrophy; gene therapy; cell therapy; dystrophin; stem cells
Skeletal muscle ischemia reperfusion injury (I-R) is a complex injury process that includes damage to the sarcolemmal membrane, contributing to necrosis and apoptosis. MG53, a muscle-specific TRIM family protein, has been shown to be essential for regulating membrane repair and has been shown to be protective against cardiac I-R and various forms of skeletal muscle injury. The purpose of this study was to determine if recombinant human MG53 (rhMG53) administration offered protection against I-R.
rhMG53 was administered to rats immediately before tourniquet-induced ischemia and again immediately before reperfusion. Two days later muscle damage was assessed histologically.
rhMG53 offered no protective effect, as evidenced primarily by similar Evans blue dye inclusion in the muscles of rats administered rhMG53 or saline.
Administration of rhMG53 does not offer protection against I-R in rat skeletal muscle. Additional studies are required to determine if the lack of a response is species-specific.
muscle injury; ischemia reperfusion; MG53; TRIM72; tourniquet
Neuropathy; Nerve tumor; Median nerve; Carpal tunnel; Hypertrophy
Testosterone (T) induces motor dysfunction in transgenic (Tg) mice overexpressing wild type androgen receptor (AR) in skeletal muscles. Since many genes implicated in motor neuron disease are expressed in skeletal muscles, mutant proteins may act in muscles to instigate muscle dysfunction in motor neuron disease.
We examined contractile properties of the extensor digitorum longus (EDL) and soleus (SOL) muscles in vitro after 5 and 3 days of T treatment in motor-impaired Tg female mice.
Both muscles showed deficits in tetanic force after 5 days of T treatment, without losses in muscle mass, protein content, or fiber number. By 3 days of T treatment, only SOL showed a deficit in tetanic force comparable to that at 5 days of treatment. In both treatments, EDL shows slowed twitch kinetics, whereas SOL shows deficits in the twitch/tetanus ratio.
These results suggest calcium handling mechanisms in muscle fibers are defective in motor-impaired mice.
testosterone; skeletal muscle; Kennedy’s disease; motor dysfunction; muscle dysfunction; neuromuscular disease
Recent in vitro studies suggest that CAPN3 deficiency leads initially to accelerated myofiber formation followed by depletion of satellite cells (SC). In normal muscle, upregulation of miR-1 and miR-206 facilitates transition from proliferating SCs to differentiating myogenic progenitors.
We examined the histopathological stages, Pax7 SC content, and muscle specific microRNA expression in biopsy specimens from well-characterized LGMD 2A patients to gain insight into disease pathogenesis.
Three distinct stages of pathological changes were identified that represented the continuum of the dystrophic process from prominent inflammation with necrosis and regeneration to prominent fibrosis, which correlated with age and disease duration. Pax7-positive SCs were highest in fibrotic group and correlated with down-regulation of miR-1, miR-133a, and miR-206.
These observations, and other published reports, are consistent with microRNA dysregulation leading to inability of Pax7-positive SCs to transit from proliferation to differentiation. This results in impaired regeneration and fibrosis.
LGMD2A; Fibrosis; microRNA; Pax; muscle regeneration
Immobilization by casting induces disuse muscle atrophy (DMA).
Using wild type (WT) and caspase-3 knockout (KO) mice, we evaluated the effect of caspase-3 on muscle mass, apoptosis and inflammation during DMA.
Caspase-3 deficiency significantly attenuated muscle mass decrease [gastrocnemius: 28 ± 1% in KO vs. 41 ± 3% in WT; soleus: 47 ± 2% in KO vs. 56 ± 2% in WT; (P < 0.05)] and gastrocnemius twitch tension decrease (23 ± 4% in KO vs. 36 ± 3% in WT, P < 0.05) at day 14 in immobilized versus contralateral hindlimb. Lack of caspase-3 decreased immobilization-induced increased apoptotic myonuclei (3.2-fold) and macrophage infiltration (2.2-fold) in soleus muscle and attenuated increased monocyte chemoattractant protein-1 mRNA expression (2-fold in KO vs. 18-fold in WT) in gastrocnemius.
Caspase-3 plays a key role in DMA and associated decreased tension, presumably by acting on the apoptosis and inflammation pathways.
skeletal muscle; inflammation; caspase-3; immobilization; apoptosis
We describe a novel, clinically applicable conduction study of the laryngeal nerves.
17 normal volunteer subjects were included. Activation of the sensory territory of the superior laryngeal nerve was performed by administration of low level, brief electrical stimulus. The laryngeal closure reflex (LCR) evoked by this stimulus was recorded by needle electrodes. Mean minimal latencies were calculated for each response, and proposed values for the upper limit of normal were determined.
Uniform consistent early ipsilateral responses and late bilateral responses, which exhibit greater variation in latency and morphology, were recorded. Significant side-to-side difference in latencies is observed, consistent with the length discrepancy between right and left recurrent laryngeal nerves.
This technique yields clear, quantifiable data regarding neurologic integrity of laryngeal function, heretofore unobtainable in the clinical setting. This study may yield clinically relevant information regarding severity and prognosis in patients with laryngeal neuropathic injury.
Laryngeal electromyography; vagus nerve; laryngeal closure reflex; brainstem reflexes; neurolaryngology
CMT1A is a slowly progressive neuropathy in which impairment is length dependent. Fibular nerve conduction studies to the anterior tibialis muscle (AT) may serve as a physiological marker of disease progression in patients with CMT1A.
Determine whether the AT compound muscle action potential (CMAP) amplitude correlates with impairment in patients with CMT1A.
We correlated AT CMAP amplitudes and impairment measured by the CMT Neuropathy Score (CMTNS) in a cross-section of 121 patients with CMT1A and a subset of 27 patients with longitudinal data.
AT CMAP amplitudes correlated with impairment as measured by the CMTNS in cross sectional analysis. Longitudinal changes in the AT CMAP showed a strong inverse correlation with leg strength but not other components of the CMTNS.
AT CMAP amplitude may serve as a useful outcome measure for physiological changes in natural history studies and clinical trials for patients with CMT1A.
Neuropathy; Charcot-Marie-Tooth Disease (CMT); Outcome measure; Charcot-Marie-Tooth Neuropathy Score (CMTNS); Nerve Conduction Studies (NCS)
Nerve conduction studies provide information regarding the status of the peripheral nerve, but relationships with sensorimotor capacities that influence mobility have not been defined.
A secondary analysis was conducted of data from 41 older subjects (20 women, age 69.1 ± 8.3 years), 25 with diabetic neuropathy of varying severity, and 16 without diabetes or neuropathy. Measurements included routine fibular motor nerve conduction studies and laboratory-based determination of ankle inversion/eversion proprioceptive thresholds and ankle inversion/eversion motor function.
Independent of age, fibular amplitude correlated robustly with ankle inversion/eversion proprioceptive thresholds (R2 = .591, p < .001), moderately with ankle inversion and eversion rates of torque generation (R2 = .216; p = .004 and R2 = .200; p = .006, respectively), and more strongly when fibular motor amplitude was normalized for body mass index (R2 = .350; p < .001 and R2 = .275; p = .001).
Fibular motor amplitude was strongly associated with ankle sensorimotor capacities that influence lateral balance and recovery from perturbations during gait. The results suggest that nerve conduction study measures have potential for an expanded clinical role in evaluating mobility function in the population studied.
Age; Balance; Diabetic Neuropathy; Muscle Strength; Proprioception
Operant conditioning can gradually change the human soleus H-reflex. The protocol conditions the reflex near M-wave threshold. This study examined its impact on the reflexes at other stimulus strengths.
H-reflex recruitment curves were obtained before and after a 24-session exposure to an up-conditioning (HRup) or down-conditioning (HRdown) protocol and were compared.
In both HRup and HRdown subjects, conditioning affected the entire H-reflex recruitment curve. In 5 of 6 HRup and 3 of 6 HRdown subjects, conditioning elevated (HRup) or depressed (HRdown), respectively, the entire curve. In the other HRup subject or the other 3 HRdown subjects, the curve was shifted to the left or to the right, respectively.
H-reflex conditioning does not simply change the H-reflex to a stimulus of particular strength; it also changes the H-reflexes to stimuli of different strengths. Thus, it is likely to affect many actions in which this pathway participates.
plasticity; motor learning; memory; rehabilitation; spinal cord
The aim of this study was to test the proficiency (accuracy among evaluators) of measured attributes
of nerve conduction (NC).
Expert clinical neurophysiologists, without instruction or consensus development, from 4 different medical centers, independently assessed 8 attributes of NC in 24 patients with diabetes mellitus (DM) on consecutive days.
No significant intraobserver differences between days 1 and 2 were found, but significant interobserver differences were seen. Use of standard reference values did not correct for these observed differences.
Interobserver variability was attributed to differences in performance of NC. It was of sufficient magnitude that it is of concern for the conduct of therapeutic trials. To deal with interrater variability in therapeutic trials, the same electromyographers should perform all NC assessments of individual patients or, preferably, NC procedures should be more standardized. A further trial is needed to test whether such standardization would eliminate interobserver variability.
clinical trial; diabetic sensorimotor polyneuropathy; nerve conduction; proficiency; standard reference value
Dlg (Discs Large) is a multidomain protein that interacts with glutamate receptors and potassium channels at Drosophila neuromuscular junctions (NMJs) and at mammalian central nervous system synapses. Dlg also localizes postsynaptically at cholinergic mammalian NMJs. We show here that α-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA) receptor subunits, together with glutamate, are present at the mammalian NMJ. Both AMPA and NMDA (N-methyl-D-aspartate) glutamate receptor subunits display overlapping postsynaptic localization patterns with Dlg at all NMJs examined in normal mice. Kir2 potassium channels also localize with Dlg and glutamate receptors at this synapse. Localization of the components of a glutamatergic system suggests novel mechanisms at mammalian neuromuscular synapses.
Dlg/SAP97; AMPA; NMDA; Kir2; neuromuscular junction
Whether there is a gender difference in fatigue and recovery from maximal velocity fatiguing contractions and across muscles is not understood.
Sixteen men and 19 women performed 90 isotonic contractions at maximal voluntary shortening velocity (maximal velocity concentric contractions, MVCC) with the elbow flexor and knee extensor muscles (separate days) at a load equivalent to 20% maximal voluntary isometric contraction (MVIC).
Power (from MVCCs) decreased similarly for men and women for both muscles (P > 0.05). Men and women had similar declines in MVIC of elbow flexors, but men had greater reductions in knee extensor MVIC force and MVIC electromyogram activity than women (P < 0.05). The decline in MVIC and power was greater, and force recovery was slower for the elbow flexors compared with knee extensors.
The gender difference in muscle fatigue often observed during isometric tasks was diminished during fast dynamic contractions for upper and lower limb muscles.
elbow flexors; gender; knee extensors; sex differences; women
Neuromuscular clinicians are often asked to evaluate the diaphragm for diagnostic and prognostic purposes. Traditionally, this evaluation is accomplished through history, physical exam, fluoroscopic sniff test, nerve conduction studies, and electromyography (EMG). Nerve conduction studies and EMG in this setting are challenging, uncomfortable, and can cause serious complications such as pneumothorax. Neuromuscular ultrasound has emerged as a non-invasive technique that can be used in the structural and functional assessment of the diaphragm. This article reviews different techniques for assessing the diaphragm using neuromuscular ultrasound and the application of these techniques to enhance diagnosis and prognosis by neuromuscular clinicians.
diaphragm; ultrasound; electromyography; nerve conduction studies; phrenic nerve injury; respiratory failure
Recovery after peripheral nerve lesions depends on guiding axons back to their targets. Polysialic acid upregulation by regrowing axons has been proposed recently as necessary for this target selectivity.
We reexamined this proposition using a cross-reinnervation model whereby axons from obturator motor neurons that do not upregulate polysialic acid regenerated into the distal femoral nerve. Our aim was to assess their target selectivity between pathways to muscle and skin.
After simple cross-repair, obturator motor neurons showed no pathway preference, but the same repair with a shortened skin pathway resulted in selective targeting of these motor neurons to muscle by a polysialic acid–independent mechanism.
The intrinsic molecular differences between motor neuron pools can be overcome by manipulation of their access to different peripheral nerve pathways such that obturator motor neurons preferentially project to a terminal nerve branch to muscle despite not upregulating the expression of polysialic acid.
femoral nerve; obturator nerve; pathway choice; PSA-NCAM; regeneration
An open-label trial suggested that valproic acid (VPA) improved strength in adults with spinal muscular atrophy (SMA). We report a 12-month, double-blind, cross-over study of VPA in ambulatory SMA adults.
There were 33 subjects, aged 20–55 years, included in this investigation. After baseline assessment, subjects were randomized to receive VPA (10–20 mg/kg/day) or placebo. At 6 months, patients were switched to the other group. Assessments were performed at 3, 6, and 12 months. The primary outcome was the 6-month change in maximum voluntary isometric contraction testing with pulmonary, electrophysiological, and functional secondary outcomes.
Thirty subjects completed the study. VPA was well tolerated, and compliance was good. There was no change in primary or secondary outcomes at 6 or 12 months.
VPA did not improve strength or function in SMA adults. The outcomes used are feasible and reliable and can be employed in future trials in SMA adults.
We report a case of a 55 year old man with non-small cell lung cancer who underwent radiation, chemotherapy with carbotaxol and paclitaxel, and left upper lobe removal two years prior to evaluation. He was referred for disabling orthostatic hypotension (113/69 supine, 66/47 mmHg standing after 10 minutes without a compensatory heart rate increase (57 to 59 bpm), fatigue, and constipation with episodes of ileus. Clinical examination showed mild ptosis bilaterally, fatiguable neck flexor weakness and hip flexor weakness. Blood pressure response to Valsalva maneuver was abnormal with absence of phase 4 overshoot and a Valsalva heart rate ratio of 1.04, The plasma norepinephrine level was low (79 pg/ml supine to 330 pg/ml standing). Single fiber EMG of the right extensor digitorum communis revealed normal mean MCD (jitter) but several pairs exceeded a jitter of 100 µs. Antibodies against muscle acetylcholine receptor [(AChR) 0.66 nmol/L, normal <0.02] and ganglionic AChR (0.34 nmol/L, normal <0.02) were present. Treatment with plasma exchange normalized responses to standing posture (105/68 supine to 118/82 mmHg standing, 66 to 79 bpm), to Valsalva (normal blood pressure overshoot, HR ratio 1.47), norepinephrine (194 pg/ml supine, 763 standing), and jitter measurements. We conclude that autoimmune autonomic ganglionopathy and myasthenia gravis can coexist and suggest that the latter should be excluded in patients with autoimmune autonomic ganglionopathy who complain of fatigue that is improved with non-supine rest.
autoimmune autonomic ganglionopathy; myasthenia gravis; paraneoplastic syndrome
Age-related decreases in tongue muscle mass and strength have been reported. It may be possible to prevent age-related tongue muscle changes using neuromuscular electrical stimulation (NMES). Our hypothesis was that alterations in muscle contractile properties and myosin heavy chain composition would be found following NMES.
Fifty-four young, middle-aged and old Fischer 344/Brown Norway rats were included. Twenty-four rats underwent bilateral electrical stimulation of the hypoglossal nerves for 8 weeks and were compared with control or sham rats. Muscle contractile properties and myosin heavy chain (MHC) in the genioglossus (GG), styloglossus (SG) and hyoglossus (HG) muscles were examined.
In comparison with unstimulated control rats, we found reduced muscle fatigue, increased contraction and half decay times and increased twitch and tetanic tension. Increased Type I MHC was found, except for GG in old and middle-aged rats.
Transitions in tongue muscle contractile properties and phenotype were found following NMES.
muscle contraction; tongue; electrical stimulation; aging; swallowing
We sought to determine if supplementation of acellular nerve allografts (ANAs) with Schwann Cells overexpressing GDNF (G-SCs) would enhance functional recovery following peripheral nerve injury.
SCs expanded in vitro were infected with a lentiviral vector to induce GDNF overexpression. Wild type-SCs (WT-SCs) and G-SCs were seeded into ANAs used to repair a 14mm nerve gap defect. Animals were harvested after 6 and 12 weeks for histomorphometric and muscle force analysis.
At 6 weeks, histomorphometry revealed that ANAs supplemented with G-SCs promoted similar regeneration compared to the isograft at midgraft. However, G-SCs failed to promote regeneration into the distal stump. At 12 weeks, ANAs with G-SCs had lower maximum and specific force production compared to controls.
The combined results suggest that consistent overexpression of GDNF by G-SCs trapped axons in the graft and prevented functional regeneration.
Peripheral nerve injury; Neurotrophic factor; Schwann cells; GDNF; Lentiviral vector; Nerve regeneration
Mutations in the valosin containing protein (VCP) gene cause hereditary Inclusion Body Myopathy (hIBM) associated with Paget disease of bone (PDB), and frontotemporal dementia (FTD). More recently they have been linked to 2% of familial ALS cases. A knock-in mouse model offers the opportunity to study VCP-associated pathogenesis.
The VCPR155H/+ knock-in mouse model was assessed for muscle strength, immunohistochemical, Western, apoptosis, autophagy and MicroPET/CT imaging analyses.
VCPR155H/+ mice developed significant progressive muscle weakness, and the quadriceps and brain developed progressive cytoplasmic accumulation of TDP-43, ubiquitin-positive inclusion bodies and increased LC3-II staining. MicroCT analyses revealed Paget-like lesions at the ends of long bones. Spinal cord demonstrated neurodegenerative changes, ubiquitin, and TDP-43 pathology of motor neurons.
VCPR155H/+ knock-in mice represent an excellent pre-clinical model for understanding VCP-associated disease mechanisms and future treatments.
Amyotrophic Lateral Sclerosis (ALS); Inclusion Body Myopathy; Paget Disease of Bone; Frontotemporal Dementia (IBMPFD); Valosin Containing Protein (VCP); molecular genetics, pathology
Manual laborers are at increased risk for carpal tunnel syndrome (CTS), and a combination of history, physical examination, and nerve conduction studies is often used to screen for CTS in this population. Neuromuscular ultrasound may be a better screening tool, because it is painless. In this study we compare the accuracy of nerve conduction studies and ultrasound for CTS screening.
Five hundred thirteen manual laborers were screened prospectively for CTS using nerve conduction studies and neuromuscular ultrasound, and the accuracy of the 2 techniques was compared using the Katz hand diagram as the diagnostic standard.
The ROC curves for the 2 techniques were not significantly different (P = 0.542), indicating that the approaches had similar diagnostic accuracy.
Neuromuscular ultrasound is a painless technique that has diagnostic accuracy similar to nerve conduction studies and can be used to screen large populations at risk for CTS.
accuracy; carpal tunnel syndrome; clinical neurophysiology; screening test; ultrasound
Surgery and childbirth can trigger attacks of hereditary brachial plexus neuropathy (HBPN), and inflammation was suggested as a component of the pathogenesis.
HBPN patients who underwent surgery or parturition from Jan.1,1996 to Dec.31,2009 were studied.
Twenty-five HBPN patients underwent 48 surgeries or parturitions. Seventeen patients (68%) had attacks, including 13 periprocedural and 7 postpartum by varied anesthesia types. Three patients who had 8 earlier combined attacks (after thyroidectomy, laminectomy, and Caesarean section) were given prophylactic immunosuppressive therapy (corticosteroids ± immunoglobulin). None suffered postoperative attacks, which is uncharacteristic of their prior experience. Five had perioperative attacks as their first HBPN manifestation. Median follow-up was 11(3-48) months. Attacks occurred in the operated limb (n=6) or distant (n=7) to surgical sites. All attacks interfered with daily living, with frequent incomplete recovery. Five patients had a SEPT9 mutation.
Corticosteroid may prevent parturition and surgical HBPN attacks in some patients. Diverse surgeries, anesthesia and childbirth frequently trigger HBPN attacks.
PLS is defined as pure upper motor neuron disease/dysfunction (PUMND) beyond 48 months after symptom onset. We know little about its early stages, but such knowledge would help to identify the mechanisms underlying PLS and ALS and determine why PLS patients seem to be protected against lower MND (LMND).
We reviewed 622 MND cases during a 4-year period and identified 34 patients with PUMND (5.4%).
Among 23 cases with follow-up data/EMGs (2 had only 1 EMG), 13 (57%) remained classified as PUMND, and 8 (35%) developed LMND (mean, 51.4 months after onset). Of these 8, LMND developed in 3 after 48 months from symptom onset. Patients with PUMND and LMND were more functionally impaired (P =.02). Separately, we identified 5 patients with PUMND who developed LMND long after 48 months (range, 50–127 months).
PLS belongs to the ALS spectrum, and perhaps all cases eventually develop LMND.
amyotrophic lateral sclerosis; lower motor neuron; upper motor neuron; pure upper motor neuron disease/dysfunction; motor neuron disease
Although there has been extensive research on small, unmyelinated fibers in the skin, little research has investigated dermal myelinated fibers in comparison. Glabrous, non-hairy skin contains mechanoreceptors that afford a vantage point for observation of myelinated fibers that have previously been seen only with invasively obtained nerve biopsies. This review discusses current morphometric and molecular expression data of normative and pathogenic glabrous skin obtained by various processing and analysis methods for cutaneous myelinated fibers. Recent publications have shed light on the role of glabrous skin biopsy in identifying signs of peripheral neuropathy and as a potential biomarker of distal myelin and mechanoreceptor integrity. The clinical relevance of a better understanding of the role of dermal myelinated nerve terminations in peripheral neuropathy will be addressed in light of recent publications in the growing field of skin biopsy.
glabrous skin biopsy; myelinated nerve fibers; molecular architecture; Meissner corpuscles; peripheral neuropathy