Reduced skeletal muscle satellite cell number alters muscle morphology after chronic stretch but allows limited serial sarcomere addition

Introduction: Muscles add sarcomeres in response to stretch, presumably to maintain optimal sarcomere length. Clinical evidence from patients with cerebral palsy, who have both decreased serial sarcomere number and reduced satellite cells (SCs), suggests a hypothesis that SCs may be involved in sarcomere addition. Methods: A transgenic Pax7‐DTA mouse model underwent conditional SC depletion, and their soleii were then stretch‐immobilized to assess the capacity for sarcomere addition. Muscle architecture, morphology, and extracellular matrix (ECM) changes were also evaluated. Results: Mice in the SC‐reduced group achieved normal serial sarcomere addition in response to stretch. However, muscle fiber cross‐sectional area was significantly smaller and was associated with hypertrophic ECM changes, consistent with fibrosis. Conclusions: While a reduced SC population does not hinder serial sarcomere addition, SCs play a role in muscle adaptation to chronic stretch that involves maintenance of both fiber cross‐sectional area and ECM structure. Muscle Nerve 55 : 384–392, 2017     

Innervation of dystrophic muscle after muscle stem cell therapy

Introduction: Duchenne muscular dystrophy (DMD) is caused by loss of the structural protein, dystrophin, resulting in muscle fragility. Muscle stem cell (MuSC) transplantation is a potential therapy for DMD. It is unknown whether donor‐derived muscle fibers are structurally innervated. Methods: Green fluorescent protein (GFP)–expressing MuSCs were transplanted into the tibials anterior of adult dystrophic mdx/mTR mice. Three weeks later the neuromuscular junction was labeled by immunohistochemistry. Results: The percent overlap between pre‐ and postsynaptic immunolabeling was greater in donor‐derived GFP⁺ myofibers, and fewer GFP⁺ myofibers were identified as denervated compared with control GFP^– fibers (P = 0.001 and 0.03). GFP⁺ fibers also demonstrated acetylcholine receptor fragmentation and expanded endplate area, indicators of muscle reinnervation (P = 0.008 and 0.033). Conclusion: It is unclear whether GFP⁺ fibers are a result of de novo synthesis or fusion with damaged endogenous fibers. Either way, donor‐derived fibers demonstrate clear histological innervation. Muscle Nerve 54 : 763–768, 2016     

Prospective study of muscle cramps in Charcot‐Marie‐Tooth disease

Introduction: This study aims to assess the frequency, location, severity, duration, and fluctuation over time of muscle cramps in Charcot‐Marie‐Tooth disease (CMT). Methods: Inherited Neuropathies Consortium Contact Registry participants recorded the occurrence and characteristics of muscle cramps using an 11‐question survey administered 3 times over 8 weeks. Results: A total of 110 adult patients with CMT completed the survey. Weekly cramp frequency was 9.3 (SD 12.3), and 23% had daily muscle cramps. Twenty‐two percent reported a significant impact on quality of life. Over 8 weeks, the daily frequency and severity of muscle cramps did not change significantly. Conclusions: Patients with CMT have muscle cramps that vary little over an 8‐week period, and they may interfere with quality of life. These data may be useful in the planning of clinical trials of agents to treat adults with CMT‐associated muscle cramps. Muscle Nerve 51: 485–488, 2015     

Outcome reliability in non‐Ambulatory Boys/Men with duchenne muscular dystrophy

Introduction: Therapeutic trials in Duchenne muscular dystrophy (DMD) often exclude non‐ambulatory individuals. Here we establish optimal and reliable assessments in a multicenter trial. Methods: Non‐ambulatory boys/men with DMD (N = 91; 16.7 ± 4.5 years of age) were assessed by trained clinical evaluators. Feasibility (percentage completing task) and reliability [intraclass correlation coefficients (ICCs) between morning and afternoon tests] were measured. Results: Forced vital capacity (FVC), assessed in all subjects, showed a mean of 47.8 ± 22% predicted (ICC 0.98). Brooke Upper Extremity Functional Rating (Brooke) and Egen Klassifikation (EK) scales in 100% of subjects showed ICCs ranging from 0.93 to 0.99. Manual muscle testing, range of motion, 9‐hole peg test, and Jebsen‐Taylor Hand Function Test (JHFT) demonstrated varied feasibility (99% to 70%), with ICCs ranging from 0.99 to 0.64. We found beneficial effects of different forms of corticosteroids for the Brooke scale, percent predicted FVC, and hand and finger strength. Conclusions: Reliable assessment of non‐ambulatory boys/men with DMD is possible. Clinical trials will have to consider corticosteroid use. Muscle Nerve 51: 522–532, 2015     

Gait and balance in essential tremor: Variable effects of bilateral thalamic stimulation

Essential tremor (ET) is a multi‐faceted condition best known for postural and action tremor but also may include disordered gait and postural instability. Deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) of the thalamus provides substantial tremor reduction yet some patients with bilateral VIM DBS have gait and balance impairment. This study examines gait and balance performance in 13 participants with ET who have bilateral VIM DBS compared with a matched control group. Participants with ET were tested with their stimulators off (DBS OFF) and on (DBS ON). For both standard and tandem walking, participants with ET walked significantly more slowly than controls, with significantly lower cadence, spending a lower percentage of the gait cycle in single limb support and a higher percentage in double support compared with controls. Participants with ET also had significantly lower tandem and one leg stance times, Berg balance scores, balance confidence, and required significantly greater time to perform the Timed Up‐and‐Go relative to controls. There were no significant differences in any gait or balance measures in the DBS OFF versus DBS ON conditions, but the effects of DBS on gait and balance were highly variable among individuals. Future studies are needed to determine why some individuals experience gait and balance difficulties after bilateral thalamic DBS and others do not. A better understanding of the mechanisms underlying gait and balance impairments in those with bilateral DBS is critical to reduce falls and fractures in this group. © 2008 Movement Disorder Society     

Sibling concordance for clinical features of Duchenne and Becker muscular dystrophies

Introduction: The correlation of markers of disease severity among brothers with Duchenne or Becker muscular dystrophy has implications for clinical guidance and clinical trials. Methods: Sibling pairs with Duchenne or Becker muscular dystrophy (n = 60) were compared for ages when they reached clinical milestones of disease progression, including ceased ambulation, scoliosis of ≥ 20°, and development of cardiomyopathy. Results: The median age at which younger brothers reached each milestone, compared with their older brothers ranged from 25 months younger for development of cardiomyopathy to 2 months older for ceased ambulation. For each additional month of ambulation by the older brother, the hazard of ceased ambulation by the younger brother decreased by 4%. Conclusions: The ages when siblings reach clinical milestones of disease vary widely between siblings. However, the time to ceased ambulation for older brothers predicts the time to ceased ambulation for their younger brothers. Muscle Nerve 49 : 814–821, 2014