Rituximab is the first drug that improves some patients with A-MAG-DP in a controlled study. The benefit may be exerted by reducing the putative pathogenic antibodies or by inducing immunoregulatory T cells. The results warrant confirmation with a larger trial.

Distinct interrelationships between inflammation and β-amyloid-associated degeneration, the two major hallmarks of the skeletal muscle pathology in sporadic inclusion body myositis (sIBM), have remained elusive. Expression of markers relevant for these pathomechanisms were analysed in biopsies of sIBM, polymyositis (PM), dermatomyositis (DM), dystrophic and non-myopathic muscle as controls, and cultured human myotubes. By quantitative PCR, a higher upregulation was noted for the mRNA-expression of CXCL-9, CCL-3, CCL-4, IFN-γ, TNF-α and IL-1β in sIBM muscle compared to PM, DM and controls. All inflammatory myopathies displayed overexpression of degeneration-associated markers, yet only in sIBM, expression of the mRNA of amyloid precursor protein (APP) significantly and consistently correlated with inflammation in the muscle and mRNA-levels of chemokines and IFN-γ. Only in sIBM, immunohistochemical analysis revealed that inflammatory mediators including IL-1β co-localized to β-amyloid depositions within myofibres. In human myotubes, exposure to IL-1β caused upregulation of APP with subsequent intracellular aggregation of β-amyloid. Our data suggest that, in sIBM muscle, production of high amounts of pro-inflammatory mediators specifically induces β-amyloid-associated degeneration. The observations may help to design targeted treatment strategies for chronic inflammatory disorders of the skeletal muscle.

Context Non-dystrophic myotonias (NDM) are rare diseases caused by mutations in skeletal muscle ion channels. Patients experience delayed muscle relaxation causing functionally-limiting stiffness and pain. Mexiletine-induced sodium channel blockade reduced myotonia in case studies and one single blind trial. As is common in rare diseases, larger studies of safety and efficacy have not previously been considered feasible. Objective To determine the effects of mexiletine for symptoms and signs of myotonia in NDM. Design, Setting, and Participation Fifty-nine patients with NDM participated in a randomized, double-blind, placebo-controlled two-period crossover study conducted between December 23, 2008 and March 30, 2011 at 7 neuromuscular referral centers in 4 countries, as part of the NIH-funded Rare Disease Clinical Research Network. Intervention Oral 200 mg mexiletine or placebo capsules three times daily for 4 weeks, followed by the opposite intervention for 4 weeks, with 1 week wash-out between periods. Main Outcome Measures Patient-reported stiffness recorded on an interactive voice response diary (IVR) was the primary endpoint (1 ‘minimal’ to 9 ‘worst ever experienced’). Secondary endpoints included IVR-reported changes in pain, weakness, and tiredness, clinical myotonia assessment, quantitative grip myotonia, Individualized Neuromuscular Quality of Life (INQoL, percent of maximal detrimental impact), SF-36, electrophysiological exercise testing, and needle EMG. Results Mexiletine significantly improved patient-reported stiffness on the IVR. Because of a statistically significant interaction between treatment and period for this outcome, primary endpoint is presented by period (period 1 means were mexiletine 2.53 versus placebo 4.21, difference −1.68, 95% Confidence Interval [CI] −2.66, −0.706, P<0.001; period 2 means were mexiletine 1.60 versus placebo 5.27, difference −3.68, 95% CI −3.85, −0.139, P=0.04). Mexiletine improved the INQoL QOL score (mexiletine 14.0, placebo 16.7, difference −2.69, 95% CI −4.07, −1.30, P<0.001) and decreased handgrip myotonia on clinical exam (seconds: mexiletine 0.164, placebo 0.494, difference −0.330, 95% CI −0.633, −0.142, P<0.001). The most common adverse effect was gastrointestinal (9 mexiletine, 1 placebo). Two participants experienced transient cardiac effects that did not require stopping the study (1 placebo, 1 mexiletine). One serious adverse event was determined to be not study-related. Conclusion In this preliminary study of patients with NDM, the use of mexiletine compared with placebo resulted in improved patient-reported stiffness over 4 weeks of treatment, despite some concern about the maintenance of blinding. Trial Registration Clinicaltrials.gov identifier: NCT 00832000

Introduction-Dermatomyositis (DM) is an autoimmune disease involving muscle and skin. Perifascicular atrophy (PFA) of myofibers is a specific and characteristic DM pathological lesion. Interferon-stimulated gene 15 (ISG15) is a ubiquitin-like modifier with a poorly understood immunological role.

The nucleic acid binding protein TDP-43 was recently identified in normal myonuclei and in the sarcoplasm of inclusion body myositis (IBM) muscle. Here we found TDP-43 sarcoplasmic immunoreactivity in 23% of IBM myofibers, while other reported IBM biomarkers were less frequent, with rimmed vacuoles in 2.8%, fluorescent Congo red material in 0.57%, SMI-31 immunoreactivity in 0.83%, and focal R1282 beta-amyloid immunoreactivity in 0.00% of myofibers. The presence of as little as > 1% of myofibers with non-nuclear sarcoplasmic TDP-43 was highly sensitive (91%) and specific (100%) to IBM among 50 inflammatory myopathy patient samples, though some patients with hereditary inclusion body myopathies and myofibrillar myopathy also had sarcoplasmic TDP-43. TDP-43 mutations were sought, and none were identified. TDP-43 could be one of many nucleic acid binding proteins that are abnormally present in IBM sarcoplasm. They could potentially interfere with the normal function of extranuclear RNAs that maintain myofiber protein production. Keywords Inclusion body myositis; inflammatory myopathies; TDP-43Inclusion body myositis (IBM) is a progressive inflammatory skeletal muscle disease with poorly understood pathogenesis. The first pathological studies of IBM muscle reported abnormalities of myonuclei that suggested nuclear degeneration was a specific aspect of this disease compared with other inflammatory myopathies.9 Subsequent studies led to the hypothesis that rimmed vacuoles in IBM muscle sections arose from the breakdown of myonuclei.8 Attempting (and failing) to confirm a report that beta-amyloid precursor protein (βAPP) transcript was present in some myofibers from patients with IBM,26 a subsequent study found instead non-specific binding of many nucleic acid probes to an unidentified DNA-binding protein in the sarcoplasm of myofibers. The nucleic acid binding protein TDP-43 was recently identified in normal muscle nuclei and also in non-nuclear sarcoplasm and around some rimmed vacuoles in IBM and inclusion body myopathy with Paget's disease and frontotemporal dementia (IBMPFD).30 The potential diagnostic value of TDP-43 immunohistochemistry for IBM was also suggested in this study by a high sensitivity and specificity for its visualization in non-nuclear regions of myofibers. Here we provide quantitative data regarding TDP-43 immunoreactivity in comparison to other reported immunohistochemical biomarkers, discuss its diagnostic value, and further clarify its distribution in IBM muscle. Methods Patients and SamplesMuscle biopsy specimens from 50 patients with inflammatory myopathies (IBM N=23; polymyositis N=9; dermatomyositis N=18), 10 patients with genetically-determined myopathies (4 with hereditary inclusion body myopathies, 2 suspected and 1 confirmed VCP mutations, and 1 suspected GNE mutation; 2 with clinical and histopathological diagnoses of myofibrillar myopathy but with unconfirmed mutations; and 1 each with confirmed mutations in dystrophin, ZNF9, calpain, and ryanodine receptor), 3 patients with n...

Objective: To study activin signaling and its blockade in sporadic inclusion body myositis (sIBM) through translational studies and a randomized controlled trial. Methods:We measured transforming growth factor b signaling by SMAD2/3 phosphorylation in muscle biopsies of 50 patients with neuromuscular disease (17 with sIBM). We tested inhibition of activin receptors IIA and IIB (ActRII) in 14 patients with sIBM using one dose of bimagrumab (n 5 11) or placebo (n 5 3). The primary outcome was the change in right thigh muscle volume by MRI at 8 weeks. Lean body mass, strength, and function were secondary outcomes. Twelve of the patients (10 bimagrumab, 2 placebo) participated in a subsequent 16-week observation phase.Results: Muscle SMAD2/3 phosphorylation was higher in sIBM than in other muscle diseases studied (p 5 0.003). Eight weeks after dosing, the bimagrumab-treated patients increased thigh muscle volume (right leg 16.5% compared with placebo, p 5 0.024; left leg 17.6%, p 5 0.009) and lean body mass (15.7% compared with placebo, p 5 0.014). Subsequently, bimagrumabtreated patients had improved 6-minute walking distance, which peaked at 16 weeks (114.6%, p 5 0.008) compared with placebo. There were no serious adverse events; the main adverse events with bimagrumab were mild acne and transient involuntary muscle contractions.Conclusions: Transforming growth factor b superfamily signaling, at least through ActRII, is implicated in the pathophysiology of sIBM. Inhibition of ActRII increased muscle mass and function in this pilot trial, offering a potential novel treatment of sIBM. Classification of evidence:This study provides Class I evidence that for patients with inclusion body myositis, bimagrumab increases thigh muscle volume at 8 weeks. Neurology ® 2014;83:2239-2246 GLOSSARY ActRII 5 activin receptors IIA and IIB; DXA 5 dual-energy x-ray absorptiometry; LBM 5 lean body mass; pSMAD2/3 5 phosphorylated SMAD2/3; QMT 5 quantitative muscle testing; sIBM 5 sporadic inclusion body myositis; 6MWD 5 6-minute walking distance; TGFb 5 transforming growth factor b; TMV 5 thigh muscle volume.Sporadic inclusion body myositis (sIBM) is a slowly progressive degenerative and inflammatory skeletal muscle disease beginning in middle or later life.1 Its clinical features include a specific pattern of muscle involvement (preferential weakness of finger flexors and knee extensors) accompanied by progressive muscle atrophy, distinctive microscopic pathology including endomysial inflammation and rimmed vacuoles, and a recently identified serum autoantibody (against cytosolic 59-nucleotidase 1A) biomarker.2-4 Despite a prominent adaptive immune response characterized by antigen-stimulated B-and T-cell maturation and prominent infiltration into muscle of immune system cells, sIBM is highly refractory to immunosuppressive therapies studied to date. 2Members of the transforming growth factor b (TGFb) superfamily of ligands signal through a heterodimeric receptor system.5 They first bind a type II receptor, such as the TGFb...

Non-dystrophic myotonias are rare diseases caused by mutations in skeletal muscle chloride and sodium ion channels with considerable phenotypic overlap between diseases. Few prospective studies have evaluated the sensitivity of symptoms and signs of myotonia in a large cohort of patients. We performed a prospective observational study of 95 participants with definite or clinically suspected non-dystrophic myotonia recruited from six sites in the USA, UK and Canada between March 2006 and March 2009. We used the common infrastructure and data elements provided by the NIH-funded Rare Disease Clinical Research Network. Outcomes included a standardized symptom interview and physical exam; the Short Form-36 and the Individualized Neuromuscular Quality of Life instruments; electrophysiological short and prolonged exercise tests; manual muscle testing; and a modified get-up-and-go test. Thirty-two participants had chloride channel mutations, 34 had sodium channel mutations, nine had myotonic dystrophy type 2, one had myotonic dystrophy type 1, and 17 had no identified mutation. Phenotype comparisons were restricted to those with sodium channel mutations, chloride channel mutations, and myotonic dystrophy type 2. Muscle stiffness was the most prominent symptom overall, seen in 66.7% to 100% of participants. In comparison with chloride channel mutations, participants with sodium mutations had an earlier age of onset of stiffness (5 years versus 10 years), frequent eye closure myotonia (73.5% versus 25%), more impairment on the Individualized Neuromuscular Quality of Life summary score (20.0 versus 9.44), and paradoxical eye closure myotonia (50% versus 0%). Handgrip myotonia was seen in three-quarters of participants, with warm up of myotonia in 75% chloride channel mutations, but also 35.3% of sodium channel mutations. The short exercise test showed ≥10% decrement in the compound muscle action potential amplitude in 59.3% of chloride channel participants compared with 27.6% of sodium channel participants, which increased post-cooling to 57.6% in sodium channel mutations. In evaluation of patients with clinical and electrical myotonia, despite considerable phenotypic overlap, the presence of eye closure myotonia, paradoxical myotonia, and an increase in short exercise test sensitivity post-cooling suggest sodium channel mutations. Outcomes designed to measure stiffness or the electrophysiological correlates of stiffness may prove useful for future clinical trials, regardless of underlying mutation, and include patient-reported stiffness, bedside manoeuvres to evaluate myotonia, muscle specific quality of life instruments and short exercise testing.

No abstract