Spinal muscular atrophy (SMA) is a disease of lower motor neurons. Motor unit number estimation (MUNE) is an electrophysiologic method to estimate the number of motor neurons innervating a muscle group. We applied the multiple point stimulation technique to the ulnar nerve–hypothenar muscle group to study lower motor neuron loss in 14 SMA subjects, including those presymptomatic, and varying from newborn through 45 years of age. Preliminary data support the value of MUNE to help understand the time course of motor neuron loss in SMA.
motor neuron disease; motor unit number estimation (MUNE); spinal muscular atrophy (SMA)
Autoantibody-induced complement activation, which causes disruption of the postsynaptic membrane, is recognized as a key pathogenic factor in myasthenia gravis (MG). Therefore, specific targeting of complement inhibitors to the site of complement activation is a potential therapeutic strategy for treatment of MG.
We assessed expression of single-chain antibody fragment–decay accelerating factor (scFv-DAF), comprising a single-chain fragment scFv1956 based on the rat complement inhibitor DAF in prokaryotic systems, and studied its inhibitory effect on complement deposition in vitro.
The recombinant conjugate scFv-DAF completely retained the wild-type binding activity of scFv1956 to AChR and inhibited complement activation of DAF in vitro.
We found that scFv-DAF could bind specifically to TE671 cells, and it is significantly more potent at inhibiting complement deposition than the untargeted parent molecule DAF. scFv-DAF may be a candidate for in vivo protection of the AChR in MG.
decay accelerating factor; fusion protein; myasthenia gravis; single-chain antibody fragment; targeting
Intrinsic mouse complement regulators influence the severity of passively induced experimental acquired myasthenia gravis (EAMG). To assess the potential influence of CD59b in the absence of CD59a background, we used the mCD59ab−/− mouse model to re-evaluate mCD59 in protecting the neuromuscular junction (NMJ).
EAMG was induced with monoclonal antibody to the acetylcholine receptor (AChR) in Daf1−/−, CD59ab−/−, Daf1−/−
CD59ab−/−, and wild-type C57Bl/6 mice. Animals were monitored throughout the experiment. Diaphragms were analyzed for NMJ injury.
CD59ab−/− mice required euthanasia 24 hours after disease induction because of severe weakness. Histological assessment demonstrated reduced AChR density, simplification of synaptic folds, and disrupted mitochondria. CD59ab-deficient mice demonstrated mild weakness and reduction in weight after 24 hours. In contrast, Daf1−/− had more severe weakness at 60 hours. The NMJ of EAMG-induced Daf1−/− and CD59ab−/− mice demonstrated similar AChR density.
NMJs of CD59 and DAF mice are protected from complement-mediated injury of passive EAMG.
complement; complement regulatory protein; myasthenia gravis; neuromuscular junction; passive EAMG
Motor unit number estimation (MUNE) of the rodent hindlimb has been used mainly for following the progression of motor neuron disorders. By performing MUNE in the tail, however, progression of axonal neuropathy could also be assessed, as both proximal and distal regions would be available for study. In this investigation, three raters performed a modified multipoint stimulation MUNE technique in the tails of 14 healthy adult rats. The technique was straightforward to perform, with a relatively narrow range of motor unit number estimates of 40 ± 16 (standard deviation) for the proximal tail and 21 ± 11 for the distal tail. Intrarater reliability coefficients were 0.31 (P = 0.033) and 0.32 (P = 0.028) for the proximal and distal tail, respectively. Interrater reliability coefficients were 0.22 (P = 0.086) and 0.44 (P = 0.004). These reliability assessments, along with the relatively low motor unit estimates and narrow range of values, support the idea that rat tail MUNE may have utility in the evaluation of rodent models of neuromuscular disease, including length-dependent neuropathy.
amyotrophic lateral sclerosis; motor neuron disease; motor unit number estimate; neuropathy; tail
We aimed to elucidate the linear makeup of each major nerve of the upper limb by the C7 root through sensory stimulation and functional MRI in a rat model.
The C7 nerve root and major nerves of the right forelimb were stimulated electrically. Blood oxygen level dependent functional magnetic resonance imaging (BOLD fMRI) was performed concurrently. Voxel overlap within the primary sensory cortex was calculated.
C7 comprises sensation in less than 1% in the musculocutaneous nerve, 6% in the ulnar nerve, 16% in the radial nerve, and 19% in the median nerve (P<0.005 for each).
The overlap is always under 25% for each major nerve.
This study helps explain why C7 is a suitable donor for brachial plexus injury treatment and why there is only a transient sensory deficit after transfer.
fMRI; C7 nerve root; peripheral nervous system; central nervous system; sensory
We investigated the effects of an acute bout of neuromuscular electrical stimulation–induced resistance exercise (NMES-RE) on intracellular signaling pathways involved in translation initiation and mechanical loading–induced muscle hypertrophy in spinal cord–injured (SCI) versus able-bodied (AB) individuals. AB and SCI individuals completed 90 isometric knee extension contractions at 30% of maximum voluntary or evoked contraction, respectively. Muscle biopsies were collected before, and 10 and 60 min after NMES-RE. Protein levels of α7- and β1-integrin, phosphorylated and total GSK-3α/β, S6K1, RPS6, 4EBP1, and FAK were assessed by immunoblotting. SCI muscle appears to be highly sensitive to muscle contraction even several years after the injury, and in fact it may be more sensitive to mechanical stress than AB muscle. Heightened signaling associated with muscle mechanosensitivity and translation initiation in SCI muscle may be an attempted compensatory response to offset elevated protein degradation in atrophied SCI muscle.
mechanotransduction; neuromuscular electrical stimulation; resistance exercise; skeletal muscle; spinal cord injury
Contradictory reports of the myosin heavy chain (MHC) composition of adult human suprahyoid muscles leave unresolved the extent to which these muscles express developmental and unconventional MHC.
By immunohistochemistry, separation SDS-PAGE-Coomassie, separation SDS-PAGE-Western blot, and mRNA PCR, we tested for conventional MHCI, MHCIIA, MHCIIX, developmental MHC embryonic and MHC neonatal, and unconventional MHC alpha-cardiac, MHC extraocular, and MHC slow tonic in adult human anterior digastric (AD), geniohyoid (GH) and mylohyoid (MH) muscles.
By separation SDS-PAGE-Coomassie and Western blot only conventional MHC are present. By immunohistochemistry all muscle fibers are positive for MHCI, MHCIIA, or MHCIIX, and fewer than 4 fibers/mm2 are positive for developmental or unconventional MHC. By PCR, mRNA of MHCI and MHCIIA dominate, with sporadically detectable MHC alpha-cardiac and without detectable mRNA of other developmental and unconventional MHC.
We conclude that human suprahyoid muscles AD, GH and MH are composed almost exclusively of conventional MHC isoforms.
Suprahyoid; swallowing; myosin heavy chain; human; muscle
Introduction: Dystrophinopathy is a rare, severe muscle disorder, and nonsense mutations are found in 13% of cases. Ataluren was developed to enable ribosomal readthrough of premature stop codons in nonsense mutation (nm) genetic disorders. Methods: Randomized, double-blind, placebo-controlled study; males ≥5 years with nm-dystrophinopathy received study drug orally 3 times daily, ataluren 10, 10, 20 mg/kg (N = 57); ataluren 20, 20, 40 mg/kg (N = 60); or placebo (N = 57) for 48 weeks. The primary endpoint was change in 6-Minute Walk Distance (6MWD) at Week 48. Results: Ataluren was generally well tolerated. The primary endpoint favored ataluren 10, 10, 20 mg/kg versus placebo; the week 48 6MWD Δ = 31.3 meters, post hoc P = 0.056. Secondary endpoints (timed function tests) showed meaningful differences between ataluren 10, 10, 20 mg/kg, and placebo. Conclusions: As the first investigational new drug targeting the underlying cause of nm-dystrophinopathy, ataluren offers promise as a treatment for this orphan genetic disorder with high unmet medical need. Muscle Nerve
50: 477–487, 2014
Duchenne muscular dystrophy; genetic; pediatric; nonsense mutation; orphan
myasthenia gravis; MuSK protein; human; B-lymphocytes; autoimmunity; rituximab
We assessed proficiency (accuracy and intra- and inter-test reproducibility) of smart quantitative sensation tests (smart QSTs) in subjects without and with diabetic polyneuropathy (DSPN).
Technologists from 3 medical centers using different but identical QSTs assessed independently 6 modalities of sensation of foot (or leg) twice in patients without (n = 6) and with (n = 6) DSPN using smart computer assisted QSTs.
Low rates of test abnormalities were observed in health and high rates in DSPN. Very high intra-class correlations were obtained between continuous measures of QSTs and neuropathy signs, symptoms, or nerve conductions (NCs). No significant intra- or inter-test differences were observed.
These results provide proof of concept that smart QSTs provide accurate assessment of sensation loss without intra- or inter-test differences useful for multicenter trials. Smart technology makes possible efficient testing of body surface area sensation loss in symmetric length-dependent sensorimotor polyneuropathies.
smart quantitative sensation tests; intra- and inter-test reproducibility; accuracy and reliability of nerve tests; neurophysiology tests; diabetic sensorimotor polyneuropathy
In this study we provide global transcriptomic profiling and analysis
of botulinum toxin A (BoNT-A)–treated muscle over a 1-year
Microarray analysis was performed on rat tibialis anterior muscles
from 4 groups (n =4/group) at 1, 4, 12, and 52
weeks after BoNT-A injection compared with saline-injected rats at 12
Dramatic transcriptional adaptation occurred at 1 week with a
paradoxical increase in expression of slow and immature isoforms, activation
of genes in competing pathways of repair and atrophy, impaired mitochondrial
biogenesis, and increased metal ion imbalance. Adaptations of the basal
lamina and fibrillar extracellular matrix (ECM) occurred by 4 weeks. The
muscle transcriptome returned to its unperturbed state 12 weeks after
Acute transcriptional adaptations resemble denervated muscle with
some subtle differences, but resolved more quickly compared with
denervation. Overall, gene expression, across time, correlates with the
generally accepted BoNT-A time course and suggests that the direct action of
BoNT-A in skeletal muscle is relatively rapid.
botulinum toxin A; cross-sectional study; microarray gene expression; neurotoxin; skeletal muscle; time course
Peripheral neuropathy is the most common neurological complication of HIV but is widely under-diagnosed in resource-limited settings. We investigated the utility of screening tools administered by non-physician health care workers (HCW) and quantitative sensory testing (QST) administered by trained individuals for identification of moderate/severe neuropathy.
We enrolled 240 HIV-infected outpatients using two-stage cluster randomized sampling. HCWs administered the several screening tools. Trained study staff performed QST. Tools were validated against a clinical diagnosis of neuropathy.
Participants were 65% women, mean age 36.4 years, median CD4 324 cells/μL. 65% were taking antiretrovirals, and 18% had moderate/severe neuropathy. The screening tests were 76% sensitive in diagnosing moderate/severe neuropathy with negative predictive values of 84–92%. QST was less sensitive but more specific.
Screening tests administered by HCW have excellent negative predictive values and are promising tools for scale-up in resource-limited settings. QST shows promise for research use.
sensitivity and specificity; HIV; peripheral nervous system diseases; developing countries; screening tools
Inherited neuropathy is a group of common neurologic disorders with heterogeneous clinical presentations and genetic causes. Detailed neuromuscular evaluations, including nerve conduction studies, laboratory testing, and histopathologic examination, can assist in identification of the inherited component beyond family history. Genetic testing increasingly enables definitive diagnosis of specific inherited neuropathies. Diagnosis, however, is often complex, and neurologic disability may have both genetic and acquired components in individual patients. The decision of which genetic test to order or whether to order genetic tests is often complicated, and the strategies to maximize the value of testing are evolving. Apart from rare inherited metabolic neuropathies, treatment approaches remain largely supportive. We provide a clinical update of the various types of inherited neuropathies, their differential diagnoses, and distinguishing clinical features (where available). A framework is provided for clinical evaluations, including the inheritance assessment, electrophysiologic examinations, and specific genetic tests.
ataxia; neuropathy; spinocerebellar; cerebellum; triplet repeats
To determine if there is an association between flexor digitorum and lumbrical muscle intrusion into the carpal tunnel and carpal tunnel syndrome (CTS).
513 manual laborers (1,026 wrists) were evaluated with ultrasound to determine if those with CTS had more muscle intrusion into the carpal tunnel than those without CTS. 190 of the participants without CTS at baseline (363 wrists) were followed over 1 year to determine if muscle intrusion at baseline predicted the development of CTS.
Participants with CTS had more muscle within the carpal tunnel with the wrist in the neutral (P = 0.026) and flexed positions (P = 0.018) than those without CTS. Baseline muscle intrusion did not predict the development of CTS at 1 year.
Muscle intrusion into the carpal tunnel is associated with CTS, but muscle intrusion alone does not predict the development of CTS over the course of a year.
Carpal tunnel syndrome; incidence; prevalence; ultrasound; EMG
The Valsalva maneuver (VM) is used widely to quantify the sensitivity of the vagal baroreflex loop (vagal baroreflex sensitivity, BRS_v), but most studies have focused on the heart rate (HR) response to blood pressure (BP) decrement (BRS_v↓), even though the subsequent response to an increment in BP following the VM (BRS_v↑) is important and different.
We evaluated recordings of HR and BP in 187 normal subjects during the VM and determined both BRS_v↑ determined by relating HR to the BP increase following phase III and BRS_v↓.
BRS_v↑ was related inversely to age. In addition, BRS_v↓, age, and magnitude of phase IV were independent predictors of BRS_v↑ in a multivariate model, accounting for 47% of the variance of BRS_v↑.
The results indicate that both BRS_v↑ and BRS_v↓ become blunted with increasing age and that these indices relate to each other.
baroreflex sensitivity; Valsalva maneuver; normal subject; age; blood pressure
We examined generalized versus joint-specific influences on muscle coactivation.
Muscle coactivation was assessed during maximal isometric and isokinetic knee and elbow joint extension moments in 48 healthy subjects (27 men). Local (joint-specific) and generalized (person-specific) contributions were examined using a combination of statistical tests, including regression with generalized estimating equations (GEEs), exploratory factor analysis, and cluster analysis.
GEEs produced similar significant coefficients for gender and joint; contraction type and test condition (angle or velocity) were not significant. Factor analysis indicated 2 joint-based factors, and cluster analysis indicated 2 groups of individuals, those with and without elevated coactivation at the knee and elbow. Women exhibited greater coactivation at both joints, but no consistent influences of angle or velocity were observed at either joint.
Muscle coactivation is a neuromuscular control response determined by local, joint-specific, and generalized, individual-specific influences.
elbow; EMG; knee; motor control; muscle cocontraction
Chemokines and their receptors are important mediators of inflammation. Guillain–Barré syndrome (GBS) is the most common cause of acute paralysis worldwide. Despite current treatments, outcomes are suboptimal. Specific chemokine receptor antagonists have the potential to be efficacious against pathogenic leukocyte trafficking in GBS.
A 36-year literature review was performed to summarize available data on chemokine expression in GBS and its representative animal model, experimental autoimmune neuritis (EAN).
Although there were a few observational human and animal studies demonstrating chemokine ligand/receptor expression in GBS and EAN, in vitro and in vivo functional studies using gene knockouts, neutralizing antibodies, or small molecular antagonists were limited. CCL2–CCR2, CCL5–CCR5, and CXCL10–CXCR3 have been most strongly implicated in EAN and GBS pathogenesis, providing targets for molecular blockade.
Preclinical human in vitro and in vivo EAN studies are needed to evaluate the potential efficacy of chemokine signaling inhibition in GBS.
chemokine; chemokine receptor; experimental autoimmune neuritis; Guillain–Barré syndrome; therapy
Contemporary natural history data in Duchenne muscular dystrophy (DMD) is
needed to assess care recommendations and aid in planning future trials.
The Cooperative International Neuromuscular Research Group (CINRG)
DMD Natural History Study (DMD-NHS) enrolled 340 individuals, aged
2–28 years, with DMD in a longitudinal, observational study at 20
centers. Assessments obtained every 3 months for 1 year, at 18 months, and
annually thereafter included: clinical history; anthropometrics; goniometry;
manual muscle testing; quantitative muscle strength; timed function tests;
pulmonary function; and patient-reported outcomes/ health-related
Glucocorticoid (GC) use at baseline was 62% present,
14% past, and 24% GC-naive. In those ≥6 years of
age, 16% lost ambulation over the first 12 months (mean age 10.8
Detailed information on the study methodology of the CINRG DMD-NHS
lays the groundwork for future analyses of prospective longitudinal natural
history data. These data will assist investigators in designing clinical
trials of novel therapeutics.
adolescent; adult; child/preschool; follow-up study; health status; human; locomotion; male; muscle strength/physiology; muscular dystrophies/classification; muscular dystrophies/Duchenne/physiopathology; muscular dystrophies/therapy; phenotype; quality of life/psychology; respiratory function test
Denervation of the paraspinal muscles in spinal disorders is frequently attributed to radiculopathy. Therefore, persons with lumbar spinal stenosis causing asymmetrical symptoms should have asymmetrical paraspinal denervation.
73 persons with clinical lumbar spinal stenosis, aged 55 to 85, completed a pain drawing and underwent masked electrodiagnostic testing including bilateral paraspinal mapping and testing of 6 muscles on the most symptomatic (or randomly chosen) limb.
With the exception of 10 subjects with unilateral thigh pain (p=0.043), there was no relationship between side of pain and paraspinal mapping score for any subgroups (symmetrical pain, pain into one calf only). Among those with positive limb EMG (tested on one side), no relationship between side of pain and paraspinal EMG score was found.
The evidence suggests that paraspinal denervation in spinal stenosis may not be due to radiculopathy, but rather due to stretch or damage to the posterior primary ramus.
Spinal stenosis; electrodiagnosis; multifidus; back pain; paraspinal mapping; segmental instability
Because of their central role in muscle development and maintenance, MEF2 family members represent excellent candidate effectors of the muscle pathology in myotonic dystrophy (DM). We investigated the expression and alternative splicing of all four MEF2 genes in muscle from neuromuscular disorder (NMD) patients, including DM1 and DM2. We observed MEF2A and MEF2C overexpression in all NMD muscle, including 12 MEF2-interacting genes. Exon 4 and 5 usage in MEF2A and MEF2C was different between DM and normal muscle, with DM showing the embryonic isoform. Similar splicing differences were observed in other NMD muscle. For MEF2C, missplicing was more pronounced in DM than in other dystrophies. Our data confirm dysregulation of MEF2A and MEF2C expression and splicing in several NMD, including DM. Our findings demonstrate that aberrant splicing in NMD is independent from expression of mutant repeats, and suggests that some aberrant splicing, even in DM, may be compensatory rather than primary.
dysregulation; MADS-domain transcription enhancer factor 2; MEF2; myotonic dystrophy; splicing
The diagnosis of amyloid myopathy is delayed when monoclonal gammopathies are not detected on initial testing and muscle biopsies are nondiagnostic, and the EMG and symptoms can mimic an inflammatory myopathy.
Case report of a patient presenting with severe progressive muscle weakness of unclear etiology despite an extensive workup including two nondiagnostic muscle biopsies.
Directed by MRI, a third biopsy revealed amyloid angiopathy and noncongophilic kappa light chain deposition in scattered subsarcolemmal rings and perimysial regions. A serum free light chain (FLC) assay revealed a kappa monoclonal gammopathy, which was not detected by multiple immunofixations.
The spectrum of immunoglobulin deposition in muscle is similar to other organs. It comprises a continuum that includes parenchymal amyloid deposition, amyloid angiopathy, and noncongophilic Light Chain Deposition Disease (LCDD). We recommend including the FLC assay in the routine investigation for monoclonal gammopathies. This case also highlights the value of MRI-guided muscle biopsy.
amyloid; gammopathy; light chain deposition; MRI; myopathy