Fiber Type Grouping Research Articles

No ageing-related increase in fibre type grouping in sprint-trained masters runners: A 10-year follow-up study.

Previous research suggests that an ageing-associated remodelling and loss of motor units due to motor neuron death contributes significantly to muscle weakness in old age. In histological sections, motor unit remodelling is reflected by increased fibre type grouping. While regular exercise may not attenuate the loss of motor units during ageing, it has been suggested to facilitate reinnervation resulting in larger motor units, and a higher number and larger fibre type groups in histological sections of muscles from aged individuals. In a 10-year follow-up study, we assessed changes in the prevalence and size of fibre type groups in the vastus lateralis muscle from 34 male masters sprinters (40-85years at start). Over the 10years, there was an ageing-related reduction in performance in the 60-m sprint (P<0.001) without significant changes in fibre type composition and fibre cross-sectional area. Neither the number of fibre type groups, defined as a fibre surrounded exclusively by fibres of the same type, nor the group size changed significantly in the 10-year period. These histological data show that there is limited to no significant fibre type grouping over a 10-year period in masters athletes who continued sprint run training. This observation challenges the paradigm that ageing, at least in systematically trained sprinters, is associated with motor unit remodelling.

The impact of life-long strength versus endurance training on muscle fiber morphology and phenotype composition in older men.

Aging is typically associated with decreased muscle strength and rate of force development (RFD), partly explained by motor unit remodeling due to denervation, and subsequent loss of fast-twitch type II myofibers. Exercise is commonly advocated to counteract this detrimental loss. However, it is unclear how life-long strength versus endurance training may differentially affect markers of denervation and reinnervation of skeletal myofibers and, in turn, affect the proportion and morphology of fast-twitch type II musculature. Thus, we compared fiber type distribution, fiber type grouping, and the prevalence of atrophic myofibers (≤1,494 µm2) in strength-trained (OS) versus endurance-trained (OE) master athletes and compared the results to recreationally active older adults (all >70 yr, OC) and young habitually active references (<30 yr, YC). Immunofluorescent stainings were performed on biopsy samples from vastus lateralis, along with leg press maximal strength and RFD measurements. OS demonstrated similar type II fiber distribution (OS: 52.0 ± 16.4%; YC: 51.1 ± 14.4%), fiber type grouping, maximal strength (OS: 170.0 ± 18.9 kg, YC: 151.0 ± 24.4 kg), and RFD (OS: 3,993 ± 894 N·s-1, YC: 3,470 ± 1,394 N·s-1) as young, and absence of atrophic myofibers (OS: 0.2 ± 0.7%; YC: 0.1 ± 0.4%). In contrast, OE and OC exhibited more atrophic fibers (OE: 1.2 ± 1.0%; OC: 1.1 ± 1.4%), more grouped fibers, and smaller proportion of type II fibers (OE: 39.3 ± 11.9%; OC: 35.0 ± 12.4%) than OS and YC (all P < 0.05). In conclusion, strength-trained master athletes were characterized by similar muscle morphology as young, which was not the case for recreationally active or endurance-trained old. These results indicate that strength training may preserve type II fibers with advancing age in older men, likely as a result of chronic use of high contractile force generation.NEW & NOTEWORTHY Aging is associated with loss of fast-twitch type II myofibers, motor unit remodeling, and grouping of myofibers. This study reveals, for the first time, that strength training preserves neural innervation of type II fibers, resulting in similar myofiber type distribution and grouping in life-long strength-trained master athletes as young moderately active adults. In contrast, life-long endurance-trained master athletes and recreationally active old adults demonstrated higher proportion of type I fibers accompanied by more marked grouping of type I myofibers, and more atrophic fibers compared with strength-trained master athletes and young individuals. Thus, strength training should be utilized as a training modality for preservation of fast-twitch musculature, maximal muscle strength, and rapid force capacity (RFD) with advancing age.

Cylindrical spirals and other concentric structures of skeletal muscle in patients with neurological diseases

Cylindrical spirals (CSs) are ultrastructurally distinct, intracytoplasmic inclusions characterized by concentrically wrapped lamellae, which are rarely found in skeletal muscle biopsies on electron microscopy (EM). CSs are often confused with other EM concentric structures including concentric laminated bodies and mitochondrial concentric cristae (MCC), due to similarities in these ultrastructures. In this study, we found CSs in 9 muscle biopsies from 9 patients, accounting for 0.5% of the biopsies examined routinely by EM. The frequency of CSs in these muscles varied from sparse and segregated to focally frequent and aggregated. CS-associated features included muscle fiber denervation atrophy in all 9 cases, fiber type grouping in 7/8 cases, tubular aggregates in 3/9 cases, and MCC in 2/9 cases. We also compared the concentric structures and highlighted their differences to distinguish CSs from other similar structures. Clinically, 8 out of 9 patients were adults aged 41–74 years and only one patient was 17 month-old. CSs were associated with several neurological diseases including Huntington's disease, amyotrophic lateral sclerosis, Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes, and other complex neurological disorders with neuropathy/encephalopathy, as well as anti-MDA5+ dermatomyositis. Eight of nine patients had genetic findings such as trinucleotide repeat expansion of huntingtin gene, ALS2 variant, MT-TL1 m.3243A > G mutation, and PMP 22 gene deletion. These results suggest that CSs may be highly variable in frequency and likely are under-reported/under-detected; they may be associated with neurogenic myopathy or central/peripheral nervous system disorders including some genetic neurological/neuromuscular diseases. Our findings of more CS-associated neurological diseases and an association of CSs with muscle neurogenic features may contribute to a better understanding of the clinico-pathological significance of CSs.

Evaluation of recurrent laryngeal neuropathy in domestic and feral horse populations in Australia using histologic and immunohistochemical analysis: A pilot study.

Little is known about potential differences in the left recurrent laryngeal nerve (Lrln) and left cricoarytenoideus dorsalis (LCAD) muscle between domestic and feral horse populations. If a difference exists, feral horses may provide a useful control population for research related to recurrent laryngeal neuropathy (RLN) and increase our understanding of potential population pressures influencing the incidence RLN. The objective of this study was to compare the Lrln and LCAD of domestic and feral horses using histological and immunohistochemical techniques (IHC). Sixteen horses, domestic (n = 8) and feral (n = 8), without clinical or ancillary examinations that were processed at an abattoir had the Lrln and LCAD muscle harvested immediately following death. Carcass weights were recorded. Subjective and morphometric histologic assessment were performed on Lrln sections. The LCAD was assessed for myosin heavy chain (fibre type proportion, diameter and grouping using IHC. Fibre-type grouping consistent with RLN was seen in both groups. Regenerating fibre clusters were more common in domestic compared to feral horses (p = 0.04). No other histologic differences occurred between groups. Muscle fibre typing demonstrated a lower mean percentage of type IIX fibres in the feral group compared to the domestic group (p = 0.03). There was no difference in type I or IIA proportions or mean diameter of any fibre type between the groups. The domestic population showed evidence of nerve regeneration suggesting RLN in this group, yet this was not supported by the higher proportion of type IIX muscle fibres compared to the feral population. Further evaluation to clarify the significance and wider occurrence of the differences is indicated.

Muscle fiber type grouping does not change in response to prolonged resistance exercise training in healthy older men

BackgroundAgeing of skeletal muscle is characterized in some by muscle fiber type grouping due to denervation-reinnervation cycles, but the severity of fiber type grouping varies widely across individuals of the same chronological age. It remains unknown whether fiber type grouping is associated with lower muscle mass and/or reduced physical function in elderly. Therefore, we assessed the relationship between fiber type grouping and indices of muscle mass and physical function in older adults. In addition, we assessed whether fiber type grouping is affected by prolonged resistance training in older adults. MethodsTwenty young (21 ± 2 y) and twenty older (70 ± 4 y) healthy men participated in the present study. Body composition (DXA-scan), quadriceps cross-sectional area (CT-scan) and muscle strength (1RM) were assessed at baseline (young and old) and following 12 weeks of resistance training (old only). Percutaneous skeletal muscle biopsies from the vastus lateralis were collected at baseline (young and old) and following exercise training (old only). Immunohistochemical analyses were performed to evaluate type I and type II muscle fiber distribution, size, myonuclear content and grouping. ResultsAt baseline, type II fibers were significantly (P < 0.05) smaller in older compared with young adults (5366 ± 1288 vs 6705 ± 1168 μm2). Whereas no differences were observed in type I, type II fiber grouping was significantly (P < 0.05) lower in older (18 ± 18 %) compared with young (32 ± 25 %) men. No significant correlations were observed between fiber type grouping and muscle mass or physical function. Prolonged resistance training in old men resulted in a significant increase (P < 0.05) in type II fiber size (from 5366 ± 1288 to 6165 ± 1484 μm2) with no significant changes in the proportion of type I muscle fibers found grouped. ConclusionMuscle fiber type grouping is not associated with lower body strength or muscle mass in healthy, older men. In addition, twelve weeks of resistance exercise training results in type II muscle fiber specific hypertrophy but does not affect fiber type grouping.

Reinnervation of Vastus lateralis is increased significantly in seniors (70-years old) with a lifelong history of high-level exercise (2013, revisited here in 2022).

In 2013 we presented results showing that at the histological level lifelong increased physical activity promotes reinnervation of muscle fibers in aging muscles. Indeed, in muscle biopsies from 70-year old men with a lifelong history of high-level physical activity, we observed a considerable increase in fiber-type groupings (F-TG), almost exclusively of the slow type. Slow-type transformation by denervation-reinnervation in senior sportsmen seems to fluctuate from those with scarce fiber-type transformation and groupings to almost fully transformed muscle, going through a process in which isolated fibers co-expressing fast and slow Myosin Heavy Chains (MHCs) seems to fill the gaps. Taken together, our results suggest that, beyond the direct effects of aging on the muscle fibers, changes occurring in skeletal muscle tissue appear to be largely, although not solely, a result of sparse denervation-reinnervation. The lifelong exercise allows the body to adapt to the consequences of the age-related denervation and to preserve muscle structure and function by saving otherwise lost muscle fibers through recruitment to different, mainly slow, motor units. These beneficial effects of high-level life-long exercise on motoneurons, specifically on the slow type motoneurones that are those with higher daily activity, and on muscle fibers, serve to maintain size, structure and function of muscles, delaying the functional decline and loss of independence that are commonly seen in late aging. Several studies of independent reserchers with independent analyses confirmed and cited our 2013 results. Thus, the results we presented in our paper in 2013 seem to have held up rather well. Trial Registration: ClinicalTrials.gov: NCT01679977

Charcot-Marie-Tooth Disease With Episodic Rhabdomyolysis Due to Two Novel Mutations in the β Subunit of Mitochondrial Trifunctional Protein and Effective Response to Modified Diet Therapy.

A 29-year-old female experienced chronic progressive peripheral neuropathy since childhood and was diagnosed with Charcot–Marie–Tooth disease (CMT) at age 15. She developed recurrent, fever-induced rhabdomyolysis (RM) at age 24. EMG studies showed decreased amplitude of compound muscle action potential, declined motor conductive velocity, and absence of sensor nerve action potential. Acylcarnitine analysis revealed elevated C16-OH, C18-OH, and C18:1-OH. Muscle biopsy showed scattered foci of necrotic myofibers invaded by macrophages, occasional regenerating fibers, and remarkable muscle fiber type grouping. Whole-exome sequencing identified two novel heterozygous mutations: c.490G>A (p.G164S) and c.686G>A (p.R229Q) in HADHB gene encoding the β-subunit of mitochondrial trifunctional protein (MTP). Reduction of long-chain fatty acid via dietary restrictions alleviated symptoms effectively. Our study indicates that the defect of the MTP β-subunit accounts for both CMT and RM in the same patient and expands the clinical spectrum of disorders caused by the HADHB mutations. Our systematic review of all MTPD patients with dietary treatment indicates that the effect of dietary treatment is related to the age of onset and the severity of symptoms.

Skeletal Muscle‐Specific Deletion of AMPKβ1β2 Modulates Age‐Induced Neuromuscular Junction Remodeling in Fast Glycolytic Muscles

The neuromuscular junction (NMJ) is the electrochemical signaling apparatus between an ⍺-motoneuron and the skeletal muscle fibers that it innervates. AMP-activated protein kinase (AMPK) regulates neuromuscular phenotype. However, the precise role of this kinase at the NMJ has yet to be elucidated. The purpose of the current study was to examine the role of skeletal muscle AMPK on NMJ biology across the lifespan. We utilized 3- and 12-month-old (mo) skeletal muscle-specific AMPKβ1β2 knock out (mKO, n = 10) and wild-type (WT, n = 10) mice, as well as 22 mo WT (n = 3) animals. The extensor digitorum longus (EDL) and soleus (SOL) muscles were examined to represent fast glycolytic and slow oxidative tissues, respectively. Utilizing confocal microscopy, we acquired 20-25 NMJ images per muscle to conduct 3D NMJ morphology analyses. Contralateral EDL and SOL muscles were also collected for immunofluorescence staining and muscle innervation determination. Quantitative real-time PCR was employed to examine genes critical for NMJ maintenance and remodeling in tibialis anterior (TA) muscles. Presynaptic axonal blebbing and sprouting was observed more frequently (p < 0.05) in the EDL and SOL muscles of aged WT animals relative to their younger counterparts. Additionally, the proportion of dysmorphic axons was greater (p < 0.05) in mKO animals compared with age-matched WT mice. As expected, there was a significant main effect of age on the total number of fragmented and ectopic NMJs in both genotypes. mKO animals displayed a greater (p < 0.05) number of dysmorphic NMJs than their age-matched WT littermates, which suggests that AMPK is required for the development and maintenance of NMJ structure. Indeed, the number of NMJs positive for postsynaptic abnormalities in the EDL muscles of 12 mo mKO animals was significantly greater than 22 mo WT mice. Fiber type grouping was significantly higher in EDL and SOL muscles of 22 mo WT animals relative to their younger counterparts. Statistical trends (p = 0.09) were also observed towards greater fiber type grouping and increased muscle fibers co-expressing multiple myosin heavy chain isoforms in only the SOL muscles of mKO animals relative to their age-matched WT controls, which suggests that AMPK elicits muscle-specific denervation/reinnervation cycling. mRNA expression of the acetylcholine receptor gamma subunit was significantly greater in mKO mice relative to WT animals. Interestingly, additional NMJ transcripts, such as agrin, rapsyn, docking protein 7, and fibroblast growth factor binding protein 1, were significantly lower in mKO animals relative to their WT littermates. Collectively, these data suggest that the absence of skeletal muscle AMPK accelerates age-associated changes at the NMJ in more glycolytic muscle fibers, potentially due to a greater ability for reinnervation in oxidative muscles. These results reveal a novel role for AMPK in the maintenance and remodeling of the NMJ during aging.

Central activation deficits contribute to post stroke lingual weakness in a rat model.

Lingual weakness frequently occurs after stroke and is associated with deficits in speaking and swallowing. Chronic weakness after stroke has been attributed to both impaired central activation of target muscles and reduced force-generating capacity within muscles. How these factors contribute to lingual weakness is not known. We hypothesized that lingual weakness due to middle cerebral artery occlusion (MCAO) would manifest as reduced muscle force capacity and reduced muscle activation. Rats were randomized into MCAO or sham surgery groups. Maximum volitional tongue forces were quantified 8 wk after surgery. Hypoglossal nerve stimulation was used to assess maximum stimulated force, muscle twitch properties, and force-frequency response. The central activation ratio was determined by maximum volitional/maximum stimulated force. Genioglossus muscle fiber type properties and neuromuscular junction innervation were assessed. Maximum volitional force and the central activation ratio were significantly reduced with MCAO. Maximum stimulated force was not significantly different. No significant differences were found for muscle twitch properties, unilateral contractile properties, muscle fiber type percentages, or fiber size. However, the twitch/tetanus ratio was significantly increased in the MCAO group relative to sham. A small but significant increase in denervated neuromuscular junctions (NMJs) and fiber-type grouping occurred in the contralesional genioglossus. Results suggest that the primary cause of chronic lingual weakness after stroke is impaired muscle activation rather than a deficit of force-generating capacity in lingual muscles. Increased fiber type grouping and denervated NMJs in the contralesional genioglossus suggest that partial reinnervation of muscle fibers may have preserved force-generating capacity, but not optimal activation patterns.NEW & NOTEWORTHY Despite significant reductions in maximum volitional forces, the intrinsic force-generating capacity of the protrusive lingual muscles was not reduced with unilateral cerebral ischemia. Small yet significant increases in denervated NMJs and fiber-type grouping of the contralesional genioglossus suggest that the muscle underwent denervation and reinnervation. Together these results suggest that spontaneous neuromuscular plasticity was sufficient to prevent atrophy, yet central activation deficits remain and contribute to chronic lingual weakness after stroke.

Immunohistochemical analysis of laryngeal muscle of horses clinically affected with recurrent laryngeal neuropathy.

As myosin heavy chain (MyHC) profile of muscle fibres is heavily influenced by neural input, changes in MyHC expression are expected in horses clinically affected with recurrent laryngeal neuropathy (RLN) yet, this has not been thoroughly investigated. To describe the changes in MyHC and fibre diameter in left cricoarytenoideus dorsalis (L-CAD) muscle of horses with clinical signs of RLN. Observational cohort study. Immunohistochemistry was used to assess the MyHC-based fibre-type proportion, size and grouping in the L-CAD of 10 Thoroughbred horses, five clinically affected with RLN and five unaffected controls based on resting endoscopic examination. The Mann-Whitney U test was used to compare the two groups. Compared to controls (of mean age 3.0±1.7years) which only expressed type I, IIA and IIX MyHC, the L-CAD of affected horses (of mean age 2.8±0.8years) had obvious fibre-type grouping, and despite apparent compensatory hypertrophy of a small number of fibres, a decrease in overall fibre diameter (median difference -35.2µm, 95% CI -47.4 to -7.9, P=.02) and diameter of type IIA fibres (median difference -46.8µm, 95% CI -52.1 to -5.0, P=.03) was observed. Anti-fast MyHC (MY32) cross-immunoreacted with embryonic-MyHC. Whereas MY32-positive fibres were identified as type IIX in controls, in affected horses these fibres were less than 50µm diameter with internal nuclei and were MYH3-positive for embryonic myosin indicating depletion of type IIX fibres, yet active regeneration and fibre renewal. Small sample size that did not include subclinical cases. Fibre size and appearance rather than staining colour were relied upon to differentiate embryonic from type IIX MyHC. Horses clinically affected with RLN have overall atrophy of fibres, loss of IIX fibres and expression of embryonic myosin indicating regenerative capacity. Despite hypertrophy of some remaining fibres, the overall decline in the bulk of fibres, including those most fatigue-resistant, may be the critical change that results in failure to maintain arytenoid abduction during exercise although direct comparison to subclinical cases is needed to confirm this.

Absence of an aging‐related increase in fiber type grouping in athletes and non‐athletes

The aging-related loss of muscle mass is thought to be partly attributable to motor neuron loss and motor unit remodeling that result in fiber type grouping. We examined fiber type grouping in 19- to 85-year-old athletes and non-athletes and evaluated to which extent any observed grouping is explained by the fiber type composition of the muscle. Since regular physical activity may stimulate reinnervation, we hypothesized that fiber groups are larger in master athletes than in age-matched non-athletes. Fiber type grouping was assessed in m. vastus lateralis biopsies from 22 young (19-27years) and 35 healthy older (66-82years) non-athletes, and 14 young (20-29years), 51 middle-aged (38-65years), and 31 older (66-85years) athletes. An "enclosed fiber" was any muscle fiber of a particular type surrounded by fibers of the same type only. A fiber type group was defined as a group of fibers with at least one enclosed fiber. Only type II fiber cross-sectional area (FCSA) showed an age-related decline that was greater in athletes (P<.001) than in non-athletes (P=.012). There was no significant age-related effect on fiber group size or fiber group number in athletes or non-athletes, and the observed grouping was similar to that expected from the fiber type composition. At face value, these observations do 1) neither show evidence for an age-related loss and remodeling of motor units nor 2) improved reinnervation with regular physical activity, but 3) histological examination may not reveal the full extent of aging-related motor unit remodeling.

Histopathologic study of extraocular muscles in thyroid-associated ophthalmopathy coexisting with ocular myasthenia gravis: a case report

BackgroundCoexistence of thyroid-associated ophthalmopathy (TAO) and ocular myasthenia gravis (OMG) is very rare. Little is known about the orbital histopathology associated with this condition. The authors reported a case of TAO coexisting with OMG and explored the histopathologic changes in extraocular muscles.Case presentationA 32-year-old man complaint of bilateral proptosis for 2 years. The patient was documented with a history of OMG and was treated with blepharoplasty to correct ptosis 3 years prior to presentation. Physical examination revealed right upper eyelid retraction resulting from the eyelid surgery. Computed tomographic scan demonstrated bilateral enlargement of the extraocular muscles. Thyroid function test confirmed hyperthyroid status. The patient was diagnosed with TAO (clinical activity score = 2/7) coexisting with OMG. Orbital decompression surgery reduced proptosis but resulted in new onset of left upper eyelid retraction because of the increased motor impulses to sustain eyelid elevation. Extraocular muscles were sampled during surgery and subjected to histopathologic stain. The stain results were analyzed against samples from age-, gender- matched TAO and control (non-TAO non-OMG) subjects. The measurement of myofiber size and glycosaminoglycan/collagen-occupied area was repeated in 3 randomly chosen fields of each slide. The variation of myofiber size was larger in the TAO + OMG (289.9 ± 142.5 μm2) samples than the TAO (544.1 ± 160.6 μm2) and control (157.0 ± 47.7 μm2) samples. Glycosaminoglycan was more abundant in the TAO + OMG (48.8 ± 12.2%) samples than the TAO (28.4 ± 3.6%) and control (3.3 ± 0.8%) samples. Collagen fibers accumulated in the TAO (60.5 ± 6.4%) samples but not in the TAO + OMG (36.1 ± 4.3%) and control (33.9 ± 2.7%) samples. Typical OMG changes were observed in the TAO + OMG samples but not in the TAO and control samples. These changes included central nuclei, aggregation of mitochondria and fiber type grouping. The histopathologic findings of TAO + OMG were summarized as inhomogeneously enlarged muscle fibers and predominantly endomysial accumulation of glycosaminoglycan.ConclusionThis study highlights the possibility of TAO coexisting with OMG and demonstrates the histopathologic features in this rare condition.

Neurogenic Muscle Biopsy Findings Are Common in Mitochondrial Myopathy.

Mitochondrial diseases (MIDs) involve peripheral nerves and skeletal muscle, but the prevalence of mitochondrial neuropathy is still unclear. Mitochondrial neuropathy has been found to correlate with muscle weakness that may be due to myopathic and/or neurogenic myopathy in patients with MIDs. We examined vastus lateralis muscle biopsies of 58 consecutive patients with mitochondrial myopathy (MM), compared with 204 consecutive non-MM patients. Muscle fiber denervation atrophy was found in 39/58 (67%) of MM patients, significantly more than 41/204 (20%) of non-MM patients and 20/58 (34%) of clinically diagnosed neuropathy. Fiber type grouping was noted in 15/58 (26%) of MM patients, significantly more than 15/204 (7%) of non-MM patients. Type 2 fiber predominance (T2FP) was identified in 7/58 (12%) of MM patients, significantly more than 1/204 (0.5%) of non-MM patients. After dividing patients into age groups, muscle fiber denervation atrophy was significantly more in MM patients aged >50 years than MM patients aged ≤50 years, without differences from all MM patients; there were no differences in fiber type grouping or T2FP between the 2 age groups. Finally, electron microscopy demonstrated MM ultrastructural changes in the neuromuscular junctions. Our findings suggest that a neurogenic component in MM is common.

Myokines in Home-Based Functional Electrical Stimulation-Induced Recovery of Skeletal Muscle in Elderly and Permanent Denervation.

Neuromuscular disorders, disuse, inadequate nutrition, metabolic diseases, cancer and aging produce muscle atrophy and this implies that there are different types of molecular triggers and signaling pathways for muscle wasting. Exercise and muscle contractions may counteract muscle atrophy by releasing a group of peptides, termed myokines, to protect the functionality and to enhance the exercise capacity of skeletal muscle. In this review, we are looking at the role of myokines in the recovery of permanent denervated and elderly skeletal muscle tissue. Since sub-clinical denervation events contribute to both atrophy and the decreased contractile speed of aged muscle, we saw a parallel to spinal cord injury and decided to look at both groups together. The muscle from lifelong active seniors has more muscle bulk and more slow fiber-type groupings than those of sedentary seniors, demonstrating that physical activity maintains slow motoneurons that reinnervate the transiently denervated muscle fibers. Furthermore, we summarized the evidence that muscle degeneration occur with irreversible Conus and Cauda Equina syndrome, a spinal cord injury in which the human leg muscles may be permanently disconnected from the peripheral nervous system. In these patients, suffering with an estreme case of muscle disuse, a complete loss of muscle fibers occurs within five to ten years after injury. Their recovered tetanic contractility, induced by home-based Functional Electrical Stimulation, can restore the muscle size and function in compliant Spinal Cord Injury patients, allowing them to perform electrical stimulation-supported stand-up training. Myokines are produced and released by muscle fibers under contraction and exert both local and systemic effects. Changes in patterns of myokine secretion, particularly of IGF-1 isoforms, occur in long-term Spinal Cord Injury persons and also in very aged people. Their modulation in Spinal Cord Injury and late aging are also key factors of home-based Functional Electrical Stimulation - mediated muscle recovery. Thus, Functional Electrical Stimulation should be prescribed in critical care units and nursing facilities, if persons are unable or reluctant to exercise. This will result in less frequent hospitalizations and a reduced burden on patients’ families and public health services.

Muscle Biopsy and Electromyography Correlation.

Introduction: In myopathies, the correlation of individual electromyographic and histopathologic findings remains poorly explored, as most previous studies have focused on the ability of muscle biopsy and electromyography to distinguish the neuropathic vs. myopathic nature of the underlying neuromuscular disease.Methods: We identified 100 patients who had a muscle biopsy and electromyography performed on identical muscles. We used a detailed grading system ranging from 0- normal to 4- severe; and graded 16 histopathologic findings in each biopsy. Electromyography findings were also graded from 0 to 4 according to the standard protocol in our EMG laboratory. We used Kendall's tau for non-parametric ordinal correlation analysis.Results: Fibrillation potentials correlated with atrophic, necrotic, and regenerating fibers, fibers harboring vacuoles, fiber splitting, fibers reacting for non-specific esterase, fibers with congophilic inclusions, inflammation (endoymysial and perimysial), and increased endomysial connective tissue. Short-duration motor unit potentials correlated with atrophic, necrotic, and regenerating fibers, increased endomysial connective tissue, and perimysial inflammation. Long-duration motor unit potentials correlated with fiber-type grouping. Increased phases of motor unit potentials correlated with atrophic fibers, increased endomysial connective tissue, and fibers reacting for non-specific esterase; while increased turns correlated with atrophic and regenerating fibers, increased endomysial connective tissue and target formations. Rapid recruitment correlated with regenerating fibers, perimysial inflammation, and increased endomysial connective tissue.Discussion: By demonstrating a clear correlation of various electromyographic and histopathologic findings, this study improves interpreting electrodiagnostic testing in myopathies, and serves as the basis to further assess the correlation between clinical, electromyographic, and histopathologic findings.

Relationships between paraspinal muscle morphology and neurocompressive conditions of the lumbar spine: a systematic review with meta-analysis

BackgroundIndividual study results have demonstrated unclear relationships between neurocompressive disorders and paraspinal muscle morphology. This systematic review aimed to synthesize current evidence regarding the relationship lumbar neurocompressive disorders may have with lumbar paraspinal muscle morphology.MethodsSearches were conducted in seven databases from inception through October 2017. Observational studies with control or comparison groups comparing herniations, facet degeneration, or canal stenosis to changes in imaging or biopsy-identified lumbar paraspinal muscle morphology were included. Data extraction and risk of bias assessment were performed by review author pairs independent of one another. Morphological differences between individuals with and without neurocompressive disorders were compared qualitatively, and where possible, standardised mean differences were obtained.ResultsTwenty-eight studies were included. Lumbar multifidus fiber diameter was smaller on the side of and below herniation for type I [SMD: −0.40 (95% CI = −0.70, −0.09) and type II fibers [SMD: −0.38 (95% CI = −0.69, −0.06)] compared to the unaffected side. The distribution of type I fibers was greater on the herniation side [SMD: 0.43 (95% CI = 0.03, 0.82)]. Qualitatively, two studies assessing small angular fiber frequency and fiber type groupings demonstrated increases in these parameters below the herniation level. For diagnostic imaging meta-analyses, there were no consistent differences across the various assessment types for any paraspinal muscle groups when patients with herniation served as their own control. However, qualitative synthesis of between-group comparisons reported greater multifidus and erector spinae muscle atrophy or fat infiltration among patients with disc herniation and radiculopathy in four of six studies, and increased fatty infiltration in paraspinal muscles with higher grades of facet joint degeneration in four of five studies. Conflicting outcomes and variations in study methodology precluded a clear conclusion for canal stenosis.ConclusionsBased on mixed levels of risk of bias data, in patients with chronic radiculopathy, disc herniation and severe facet degeneration were associated with altered paraspinal muscle morphology at or below the pathology level. As the variability of study quality and heterogeneous approaches utilized to assess muscle morphology challenged comparison across studies, we provide recommendations to promote uniform measurement techniques for future studies.Trial registrationPROSPERO 2015: CRD42015012985

Quantitation of muscle pathology abnormalities in 18 patients with mitochondrial disorders

ABSTRACT INTRODUCTION: Mitochondrial disorders can lead to the accumulation of mitochondria in muscle fibers, as indicated by ragged red (RRF) or ragged blue fibers when stained with modified Gomori trichrome or succinate dehydrogenase (SDH+), respectively, and, absence of activity of cytochrome c oxidase, COX negative fibers (COX-). The combined COX-SDH stain (COMBO+) can reveal even more COX-deficient fibers. OBJECTIVE: To quantify RRFs, SDH+, COX-, and COMBO+ fibers in muscle biopsies with mitochondrial findings. MATERIAL AND METHODS: We retrospectively selected 18 muscle biopsies with mitochondrial abnormalities based on the Walker criteria (percentage of RRFs/COX- fibers, and clinical picture), and/or the Sleigh criteria (percentage of RRFs, SDH+, and COX- fibers). RESULTS: Females represented 83.3%, with a mean age of 38.6 years (5 months-70 years). Patients were diagnosed with chronic progressive external ophthalmoplegia (CPEO, 66.7%), proximal myopathy (22.2%), idiopathic hyperCKemia (11.1%), Kearns-Sayre syndrome (5.6%), mitochondrial encephalomyopathy with ragged red fibers and stroke-like episodes (5.6%), and a dystrophic pattern (5.6%). Some cases of CPEO were combined with proximal myopathy. The quantitative pathologic findings were: RRFs, 3.95% ± 3.17%; SDH+, 7.55% ± 6.1%; COX-, 10.9% ± 7.2%; COMBO+, 14.22% ± 12.79%. We found a slight variation in the diameter of muscle fibers, no necrosis or proliferative connective tissue, few fibers with internal nuclei, and some cases with fiber type grouping. CONCLUSION: Pathologic events, grouped in ascending order of frequency, were RRFs, SDH+ fibers, COX- fibers, and COMBO+ fibers. These data emphasize the importance of the COMBO technique in revealing occult COX deficiency in muscle fibers.

Immunohistochemical analysis of canine and feline muscle disorders using formalin-fixed, paraffin-embedded tissues.

Histochemical techniques used in examination of muscle biopsies typically require frozen sections. Given that most of the specimens submitted to a veterinary laboratory for diagnosis are formalin-fixed, the choice of staining methods is limited. We aimed to further advance the diagnostic capabilities of pathologists presented with formalin-fixed muscle samples and to describe the differences in immunohistopathologic findings between neurogenic and myogenic muscle disorders. Based on hematoxylin and eosin staining, we defined in dogs the histologic lesions in 4 neurogenic disorders (degenerative myelopathy and polyneuropathy) and 2 myogenic disorders (dystrophin-deficient muscular dystrophy). In cats, we defined the lesions in 2 neurogenic disorders (lymphoma of nerve roots and spinal cords) and 1 myogenic disorder (laminin α2-deficient muscular dystrophy). Immunohistochemistry for slow and fast myosins revealed angular and group atrophy of type 1 and type 2 fibers in dogs and cats, and fiber type grouping in dogs. These immunohistopathologic findings were specific to neurogenic muscle disorders. Immunohistochemistry for nestin and myogenin revealed nestin-positive fibers and myogenin-positive nuclei in dogs and cats. They were not specific, but these fibers in myogenic disorders can be interpreted as regenerating fibers. The immunohistochemical method described herein appears to be useful for discriminating neurogenic and myogenic disorders in formalin-fixed, paraffin-embedded muscle tissue of dogs and cats.

Maintaining motor units into old age: running the final common pathway

Invited Letter to the Editor. This article is a commentary on the recently published manuscript "Use it or lose it: tonic activity of slow motoneurons promotes their survival and preferentially increases slow fiber-type groupings in muscles of old lifelong recreational sportsmen". Mosole S, Carraro U, Kern H, Loefler S, Zampieri S. Use it or lose it: tonic activity of slow motoneurons promotes their survival and preferentially increases slow fiber-type groupings in muscles of old lifelong recreational sportsmen. Eur J Transl Myol 2016;26:5972. doi: 10.4081/ejtm.2016.5972. We offer some unique perspectives on masters athletes and the role of physical activity in maintaining the number and function of motor units into old age.

Use it or Lose It: Tonic Activity of Slow Motoneurons Promotes Their Survival and Preferentially Increases Slow Fiber-Type Groupings in Muscles of Old Lifelong Recreational Sportsmen.

Histochemistry, immuno-histochemistry, gel electrophoresis of single muscle fibers and electromyography of aging muscles and nerves suggest that: i) denervation contributes to muscle atrophy, ii) impaired mobility accelerates the process, and iii) lifelong running protects against loss of motor units. Recent corroborating results on the muscle effects of Functional Electrical Stimulation (FES) of aged muscles will be also mentioned, but we will in particular discuss how and why a lifelong increased physical activity sustains reinnervation of muscle fibers. By analyzing distribution and density of muscle fibers co-expressing fast and slow Myosin Heavy Chains (MHC) we are able to distinguish the transforming muscle fibers due to activity related plasticity, to those that adapt muscle fiber properties to denervation and reinnervation. In muscle biopsies from septuagenarians with a history of lifelong high-level recreational activity we recently observed in comparison to sedentary seniors: 1. decreased proportion of small-size angular myofibers (denervated muscle fibers); 2. considerable increase of fiber-type groupings of the slow type (reinnervated muscle fibers); 3. sparse presence of muscle fibers co-expressing fast and slow MHC. Immuno-histochemical characteristics fluctuate from those with scarce fiber-type modulation and groupings to almost complete transformed muscles, going through a process in which isolated fibers co-expressing fast and slow MHC fill the gaps among fiber groupings. Data suggest that lifelong high-level exercise allows the body to adapt to the consequences of the age-related denervation and that it preserves muscle structure and function by saving otherwise lost muscle fibers through recruitment to different slow motor units. This is an opposite behavior of that described in long term denervated or resting muscles. These effects of lifelong high level activity seems to act primarily on motor neurons, in particular on those always more active, i.e., on the slow motoneurons. The preferential reinnervation that follows along decades of increased activity maintains neuron and myofibers. All together the results open interesting perspectives for applications of FES and electroceuticals for rejuvenation of aged muscles to delay functional decline and loss of independence that are unavoidable burdens of advanced aging.Trial Registration: ClinicalTrials.gov: NCT01679977