Update in inclusion body myositis

Autoantibodies against a subunit of mitochondrial respiratory chain complex I in inclusion body myositis

BACKGROUND

Autoantibodies are found in up to 80 % of patients with idiopathic inflammatory myopathies (IIM) and are associated with distinct clinical phenotypes. Autoantibodies targeting cytosolic 5'-nucleotidase 1A (anti-NT5C1A) are currently the only known serum biomarker for the subgroup inclusion body myositis (IBM), although detected even in other autoimmune diseases. The aim of the study was to identify new autoimmune targets in IIM.

METHODS

In a first cross-sectional exploratory study, samples from 219 IIM (108 Polymyositis (PM), 80 Dermatomyositis (DM) and 31 IBM) patients, 349 Systemic Lupus Erythematosus (SLE) patients and 306 population controls were screened for IgG reactivity against a panel of 357 proteins using an antigen bead array. All samples were identified in the local biobank of the Rheumatology clinic, Karolinska University Hospital. Positive hits for the IBM subgroup were then validated in an independent larger cohort of 287 patients with IBM followed at nine European rheumatological or neurological centers. IBM serum samples were explored by antigen bead array and results validated by Western blot. As controls, sera from 29 patients with PM and 30 with DM, HLA-matched with the Swedish IBM cohort, were included. Demographics, laboratory, clinical, and muscle biopsy data of the IBM cohort was retrieved.

RESULTS

In the exploratory study, IgG reactivity towards NADH dehydrogenase 1 α subcomplex 11 (NDUFA11), a subunit of the membrane-bound mitochondrial respiratory chain complex I, was discovered with higher frequency in the IBM (9.7 %) than PM (2.8 %) and DM samples (1.3 %), although the difference was not statistically significant. Anti-NDUFA11 IgG was also found in 1.4 % of SLE and 2.0 % of population control samples. In the validation study, anti-NDUFA11 autoantibodies were detected in 10/287 IBM patients (3.5 %), 0/29 p.m. and 0/30 DM patients. Reactivity against NDUFA11 could be confirmed by Western blot. No statistically significant differences were found between patients with and without anti-NDUFA11 antibodies when comparing clinical, laboratory and histological data. However, we observed a trend of higher frequency of distal lower extremity muscle weakness, ragged red fibers and higher CK levels at time of diagnosis in the anti-NDUFA11 positive group. Co-existence of anti-NDUFA11 and anti-NT5C1A antibodies was not observed in any IBM patient.

CONCLUSION

Our results reveal a new autoimmune target in the mitochondrial respiratory chain complex I that might be specifically associated with IBM. This is of particular interest as mitochondrial abnormalities are known histological findings in muscle biopsies of IBM patients.

Current biomarkers in inclusion body myositis

Inclusion body myositis (IBM) is an idiopathic muscle disorder primarily affecting adults above the age of 50. IBM is characterized by weakness in the knee extensor and deep finger flexor muscles due to muscle atrophy and fibroadipose replacement. Dynamometry and manual muscle testing are commonly used to assess patient muscle strength, while magnetic resonance imaging and electromyography studies identify the patterns of muscle atrophy and motor unit potentials. Although the underlying pathophysiological mechanisms of IBM are still unknown, common histopathological markers include rimmed vacuoles and inclusions. The immune system is also largely implicated in pathogenesis, as skeletal muscle in IBM overexpresses major histocompatibility complex I (MHC-I), and cluster of differentiation (CD) 8+ T-cells, and features endomysial inflammation. Antibodies to the cytosolic 5'-nucleotidase 1A (cN1A) protein have been associated with IBM but have low sensitivity and specificity. As many classic features of IBM present only in advanced stages of disease, there are substantial challenges to the diagnosis and monitoring of IBM progression in its early stages. Identifying early diagnostic biomarkers and new biomarker signatures associated with IBM disease progression is necessary for clinical trial readiness.

Study to Assess Content Validity and Interrater and Intrarater Reliability of the Inclusion Body Myositis Functional Rating Scale

Background and Objectives

Sporadic inclusion body myositis (IBM) is a rare, muscle-wasting disease that negatively affects health-related quality of life. Although a measure that has been developed to assess the impact of IBM, the IBM Functional Rating Scale (IBMFRS) has limited evidence of content validity or reliability, and what constitutes a meaningful change threshold; this study was conducted to address these gaps.

Methods

Adult patients with a clinical diagnosis of IBM from the United Kingdom and disease area expert health care professionals from the United States and United Kingdom took part in this study. This study consisted of 5 stages including phone interviews (physicians), face-to-face interviews (patients), face-to-face ratings, phone ratings, and ratings of videos using the IBMFRS.

Results

The IBMFRS adequately captures all core functional impacts of IBM, which was corroborated by both patient participants and physicians when debriefing the measure. Physicians and patient participants all thought any change on the measure would be meaningful change for a patient, either improvement or worsening. The quantitative analysis demonstrated good interrater reliability for face-to-face ratings (intraclass correlation coefficient [ICC] >0.7) and for video ratings (ICC >0.9). Intrarater reliability was excellent for face-to-face and video ratings (ICC >0.9). Equivalence between the modes of administration, face-to-face vs phone, was also excellent (ICC >0.9).

Discussion

The IBMFRS is content valid in assessing the key functional impacts of IBM, and any change would be meaningful. It is reliable both within and across raters, and there is equivalence between different modes of administration (face-to-face vs phone).

Inclusion body myositis: from genetics to clinical trials

Inclusion body myositis (IBM) belongs to the group of idiopathic inflammatory myopathies and is characterized by a slowly progressive disease course with asymmetric muscle weakness of predominantly the finger flexors and knee extensors. The disease leads to severe disability and most patients lose ambulation due to lack of curative or disease-modifying treatment options. Despite some genes reported to be associated with hereditary IBM (a distinct group of conditions), data on the genetic susceptibility of sporadic IBM are very limited. This review gives an overview of the disease and focuses on the current genetic knowledge and potential therapeutic implications.

Longitudinal Changes in MRI Muscle Morphometry and Composition in People With Inclusion Body Myositis

BACKGROUND AND OBJECTIVES

Limited data suggest that quantitative MRI (qMRI) measures have potential to be used as trial outcome measures in sporadic inclusion body myositis (sIBM) and as a noninvasive assessment tool to study sIBM muscle pathologic processes. Our aim was to evaluate changes in muscle structure and composition using a comprehensive multiparameter set of qMRI measures and to assess construct validity and responsiveness of qMRI measures in people with sIBM.

METHODS

This was a prospective observational cohort study with assessments at baseline (n = 30) and 1 year (n = 26). qMRI assessments include thigh muscle volume (TMV), inter/intramuscular adipose tissue (IMAT), muscle fat fraction (FF), muscle inflammation (T2 relaxation time), IMAT from T2* relaxation (T2*-IMAT), intermuscular connective tissue from T2* relaxation (T2*-IMCT), and muscle macromolecular structure from the magnetization transfer ratio (MTR). Physical performance assessments include sIBM Physical Functioning Assessment (sIFA), 6-minute walk distance, and quantitative muscle testing of the quadriceps. Correlations were assessed using the Spearman correlation coefficient. Responsiveness was assessed using the standardized response mean (SRM).

RESULTS

After 1 year, we observed a reduction in TMV (6.8%, p < 0.001) and muscle T2 (6.7%, p = 0.035), an increase in IMAT (9.7%, p < 0.001), FF (11.2%, p = 0.030), connective tissue (22%, p = 0.995), and T2*-IMAT (24%, p < 0.001), and alteration in muscle macromolecular structure (ΔMTR = -26%, p = 0.002). A decrease in muscle T2 correlated with an increase in T2*-IMAT (r = -0.47, p = 0.008). Deposition of connective tissue and IMAT correlated with deterioration in sIFA (r = 0.38, p = 0.032; r = 0.34, p = 0.048; respectively), whereas a decrease in TMV correlated with a decrease in quantitative muscle testing (r = 0.36, p = 0.035). The most responsive qMRI measures were T2*-IMAT (SRM = 1.50), TMV (SRM = -1.23), IMAT (SRM = 1.20), MTR (SRM = -0.83), and T2 relaxation time (SRM = -0.65).

DISCUSSION

Progressive deterioration in muscle quality measured by qMRI is associated with a decline in physical performance. Inflammation may play a role in triggering fat infiltration into muscle. qMRI provides valid and responsive measures that might prove valuable in sIBM experimental trials and assessment of muscle pathologic processes.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that qMRI outcome measures are associated with physical performance measures in patients with sIBM.

The health-related quality of life, mental health and mental illnesses of patients with inclusion body myositis (IBM): results of a mixed methods systematic review

Background

Inclusion body myositis (IBM) is a rare neuromuscular disease (NMD) and effective therapies are not available. Thus, it is relevant to determine the health-related quality of life (HRQoL) in IBM patients including aspects of mental health and illnesses.

Objectives

To identify and summarize the assessment of HRQoL, mental health and illnesses in IBM, the major factors that determine and influence them as well as the respective influence of IBM in general and compared to other NMD as a systematic review.

Methods

We performed a mixed methods systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The search was conducted within the databases PubMed, PsycINFO, LIVIVO and the Cochrane Database. Data were narratively summarized and categorized in the physical, psychological and social HRQoL dimensions.

Results

The systematic screening totalled 896 articles. Six studies were finally identified, comprising of 586 IBM patients. The applied patient reported outcome measures (PROMs) varied. Quantitatively, the main physical impairments (e.g. weakness, functioning, role perception) were assessed using the general population or other NMD as comparators. Results on social and psychological HRQoL were frequently inconsistent. Qualitatively, psychological and social limitations accompanied IBM related physical deteriorations.

Conclusions

A research gap exists regarding rigour determinants of HRQoL and mental illness in IBM. In-depth qualitative studies could help to prepare the ground for the assessment of long-term HRQoL data combined with appropriately focussed psychological PROMs advancing the understanding of the HRQoL in IBM throughout the course of the disease from a patient perspective.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02382-x.

Muscle Sonography in Inclusion Body Myositis: A Systematic Review and Meta-Analysis of 944 Measurements

Inclusion body myositis (IBM) is a slowly progressive muscle weakness of distal and proximal muscles, which is diagnosed by clinical and histopathological criteria. Imaging biomarkers are inconsistently used and do not follow international standardized criteria. We conducted a systematic review and meta-analysis to investigate the diagnostic value of muscle ultrasound (US) in IBM compared to healthy controls. A systematic search of PubMed/MEDLINE, Scopus and Web of Science was performed. Articles reporting the use of muscle ultrasound in IBM, and published in peer-reviewed journals until 11 September 2021, were included in our study. Seven studies were included, with a total of 108 IBM and 171 healthy controls. Echogenicity between IBM and healthy controls, which was assessed by three studies, demonstrated a significant mean difference in the flexor digitorum profundus (FDP) muscle, which had a grey scale value (GSV) of 36.55 (95% CI, 28.65-44.45, p < 0.001), and in the gastrocnemius (GC), which had a GSV of 27.90 (95% CI 16.32-39.48, p < 0.001). Muscle thickness in the FDP showed no significant difference between the groups. The pooled sensitivity and specificity of US in the differentiation between IBM and the controls were 82% and 98%, respectively, and the area under the curve was 0.612. IBM is a rare disease, which is reflected in the low numbers of patients included in each of the studies and thus there was high heterogeneity in the results. Nevertheless, the selected studies conclusively demonstrated significant differences in echogenicity of the FDP and GC in IBM, compared to controls. Further high-quality studies, using standardized operating procedures, are needed to implement muscle ultrasound in the diagnostic criteria.

Musculoskeletal Ultrasound in Inclusion Body Myositis: A Comparative Study with Magnetic Resonance Imaging

The objective of this study was to compare the accuracy of ultrasound (US) with that of magnetic resonance imaging (MRI) in identifying muscle abnormalities in patients with inclusion body myositis (IBM). Twelve patients with IBM underwent muscle US and MRI on the same day. Twelve muscle groups were analyzed per patient. On US, a visual grading system was used to detect whether the muscles were affected. On MRI, muscle atrophy, fat infiltration and edema patterns were analyzed. The inter- and intra-reader reproducibility was similar for US and MRI in the evaluation of muscle abnormalities. All patients with muscle abnormalities identified on US presented with fat infiltration on MRI, which was the most common abnormality identified on MRI. Most importantly, the accuracy of US compared with that of MRI for the detection of muscle abnormalities in patients with IBM was 86.8 (κ coefficient = 0.632), with a sensitivity of 84% and specificity of 100%. In conclusion all patients with muscle abnormalities identified on US presented with fat infiltration on MRI, and the marked increase in echo intensity observed in the muscles of IBM patients was related mostly to fatty replacement. Most importantly, US exhibited significant accuracy compared with MRI.

Differential Diagnoses of Inclusion Body Myositis

Inclusion body myositis is a slowly progressive myopathy, characteristically affecting quadriceps and long finger flexors. Atypical presentations do occur, however, and there is overlap with other myopathies, including inflammatory and hereditary etiologies. This article discusses atypical cases and differential diagnoses and considers the role of imaging and histopathology in differentiating inclusion body myositis.

Inclusion body myositis in the rheumatology clinic

Inclusion body myositis is a rare sporadic inflammatory-degenerative myopathy of the elderly. Despite being the commonest type of acquired myopathy after the age of 50, misdiagnosis is extremely common. The most frequent hurdle in identifying new cases is the wrong diagnosis of polymyositis or motor neuron disease. Novel insights into pathogenic mechanisms have heralded the quest for newer therapeutics as well as drug repurposing in this otherwise progressive disorder.

Quantitative muscle MRI study of patients with sporadic inclusion body myositis

BACKGROUND

Fat infiltration in individual muscles of sporadic inclusion body myositis (sIBM) patients has rarely been assessed.

METHODS

Sixteen sIBM patients were assessed using MRI of the thighs and lower legs (LL). The severity of fat infiltration, proximal-to-distal and side asymmetries, and the correlations with clinical and functional parameters were investigated.

RESULTS

All the patients had fat-infiltrated muscles, and thighs were more severely affected than LL. A proximal-to-distal gradient of fat infiltration was mainly observed for adductors, quadriceps, sartorius, and medial gastrocnemius muscles. A strong negative correlation was observed between the whole muscle fat fraction in the thighs and LL and the Inclusion Body Myositis Functional Rating Scale and Medical Research Council scores for the lower limbs.

CONCLUSIONS

Fat infiltration in individual muscles of sIBM patients is heterogeneous in terms of proximal-to-distal gradient and severity was correlated with clinical scores. These results should be considered for both natural history investigation and clinical trials.

Effect of intravenous immunoglobulin therapy on anti-NT5C1A antibody-positive inclusion body myositis after successful treatment of hepatitis C: A case report

Inclusion body myositis (IBM) is the commonest idiopathic inflammatory myopathy of older persons. Pathophysiological mechanism of IBM remains unknown; however, an association of IBM with chronic hepatitis C virus (HCV) infection and serum autoantibodies against skeletal muscle protein 5′-nucleotidase 1A (NT5C1A) has recently been reported. No effective treatment for IBM has yet been developed. We here present a 70-year-old man who was anti-NT5C1A antibody-positive in association with IBM and chronic hepatitis C. The initial treatment of ombitasvir/paritaprevir/ritonavir for his chronic hepatitis C was successful; however, his symptoms of IBM did not improve. On the contrary, his quadriplegic paralysis became more severe and he developed dysphagia. Next, steroid pulse therapy was initiated for IBM and, although his hyper-creatine phosphokinase-emia improved, his symptoms did not; indeed, they worsened. Subsequent intravenous immunoglobulin therapy (IVIg) resulted in obvious improvement in his dysphagia. Thereafter IVIg therapy was repeated at approximately 2-monthly intervals. His dysphagia remained improved for more than 1 year; however, his quadriplegia continued to progress slowly. Although IBM can reportedly be associated with hepatitis C, we inferred that there was no direct relationship between these conditions in our patient because his IBM did not improve after treatment of his hepatitis C. Although his IBM-associated quadriplegia did not improve, IVIg therapy did result in improvement in his dysphagia.

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Coexisting anti-NT5C1A antibody+ inclusion body myositis and chronic hepatitis C

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Symptoms of IBM did not improve with successful treatment of hepatitis C.

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Videofluoroscopic examination confirmed improvement in dysphagia with IVIg therapy.

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Repeated IVIg therapy resulted in persistent improvement in dysphagia over 1 year.

Immunohistochemical and ultrastructural analysis of sporadic inclusion body myositis: a case series

Sporadic inclusion body myositis (s-IBM) is a progressive, skeletal muscle disease with poor prognosis. However, establishing the final diagnosis is difficult because of the lack of clear biomarkers in the blood serum and very slow development of clinical symptoms. Moreover, most other organs function normally without any disturbance. Here, in patients with this untreatable disease, we have underlined the importance of immunohistochemical and ultrastructural assessment of skeletal muscle in patients diagnosed with s-IBM. The goal of this study was to identify the distribution of specific antigens and to determine morphological features in order to localize pathological protein aggregates, rimmed vacuoles, and loss of myofibrils, which are key elements in the diagnosis of s-IBM. All studied patients were between 48 and 83 years of age and were hospitalized in the Department of Rheumatology and Internal Medicine between 2011 and 2016. Anamneses revealed an accelerated progression of muscle atrophy, weakness of limb muscles, and difficulties with climbing stairs. Based on histopathology and transmission electron microscopy examination, inflammatory infiltrations consisting of mononuclear cells, severe atrophy and focal necrosis of myofibers, splitting of myofilaments, myelinoid bodies and rimmed vacuoles were observed. Primary antibodies directed against CD3, CD8, CD68, cN1A, beta-amyloid, Tau protein and apolipoprotein B made it possible to identify types of cells within infiltrations as well as the protein deposits within myofibers. Using a combination of immunohistochemistry and electron microscopy methods, we were able to establish the correct final diagnosis and to implement a specific treatment to inhibit disease progression.

Concomitant occurrence of FXTAS and clinically defined sporadic inclusion body myositis: report of two cases

This report describes unique presentations of inclusion body myositis (IBM) in two unrelated patients, one male and one female, with genetically and histologically confirmed fragile X-associated tremor/ataxia syndrome (FXTAS). We summarize overlapping symptoms between two disorders, clinical course, and histopathological analyses of the two patients with FXTAS and sporadic IBM, clinically defined per diagnostic criteria of the European Neuromuscular Centre. In case 1, a post-mortem analysis of available brain and muscle tissues is also described. Histopathological features (rimmed vacuoles) consistent with clinically defined IBM were detected in both presented cases. Postmortem testing in case 1 revealed the presence of an FMR1 premutation allele of 60 CGG repeats in both brain and skeletal muscle samples. Case 2 was a premutation carrier with 71 CGG repeats who had a son with FXS. Given that FXTAS is associated with immune-mediated disorders among premutation carriers, it is likely that the pathogeneses of IBM and FXTAS are linked. This is, to our knowledge, the first report of these two conditions presenting together, which expands our understanding of clinical symptoms and unusual presentations in patients with FXTAS. Following detection of a premutation allele of the FMR1 gene, FXTAS patients with severe muscle pain should be assessed for IBM.

Development and evaluation of a standardized ELISA for the determination of autoantibodies against cN-1A (Mup44, NT5C1A) in sporadic inclusion body myositis

PURPOSE

Sporadic inclusion body myositis (sIBM) is an autoimmune degenerative disease of the muscle, with inflammatory infiltrates and inclusion vacuoles. Its pathogenesis is not fully understood and the diagnosis is hampered by its imprecise characteristics, at times indistinguishable from other idiopathic inflammatory myopathies such as polymyositis and dermatomyositis. The diagnosis may be assisted by the detection of autoantibodies targeting Mup44, a skeletal muscle antigen identified as cytosolic 5'-nucleotidase 1A (cN-1A, NT5C1A). A novel standardized anti-cN-1A IgG ELISA was developed and its diagnostic performance was evaluated by two reference laboratories.

METHODS

Recombinant human full-length cN-1A was expressed and purified, and subsequently utilized to set up a standardized ELISA. To evaluate the novel assay, laboratory A examined sera from North American patients with clinically and pathologically diagnosed definite sIBM (n = 17), suspected sIBM (n = 14), myositis controls (n = 110), non-myositis autoimmune controls (n = 93) and healthy subjects (n = 52). Laboratory B analyzed a Dutch cohort of definite sIBM patients (n = 51) and healthy controls (n = 202).

RESULTS

Anti-cN-1A reactivity was most frequent in definite sIBM (39.2-47.1%), but absent in biopsy-proven classic polymyositis or dermatomyositis. Overall diagnostic sensitivity and specificity amounted to 35.5 and 96.1% (laboratory A) and 39.2 and 96.5% (laboratory B).

CONCLUSIONS

Anti-cN-1A autoantibodies were detected by ELISA with moderate sensitivity, but high specificity for sIBM and may therefore help diagnose this infrequent and difficult-to-diagnose myopathy. The novel anti-cN-1A IgG ELISA can improve and accelerate the diagnosis of sIBM using sera where muscle biopsy is delayed or unfeasible.

Targeting protein homeostasis in sporadic inclusion body myositis

Sporadic inclusion body myositis (sIBM) is the commonest severe myopathy in patients more than 50 years of age. Previous therapeutic trials have targeted the inflammatory features of sIBM but all have failed. Because protein dyshomeostasis may also play a role in sIBM, we tested the effects of targeting this feature of the disease. Using rat myoblast cultures, we found that up-regulation of the heat shock response with arimoclomol reduced key pathological markers of sIBM in vitro. Furthermore, in mutant valosin-containing protein (VCP) mice, which develop an inclusion body myopathy, treatment with arimoclomol ameliorated disease pathology and improved muscle function. We therefore evaluated arimoclomol in an investigator-led, randomized, double-blind, placebo-controlled, proof-of-concept trial in sIBM patients and showed that arimoclomol was safe and well tolerated. Although arimoclomol improved some IBM-like pathology in the mutant VCP mouse, we did not see statistically significant evidence of efficacy in the proof-of-concept patient trial.

Medication of inclusion body myositis: a systematic review

To investigate the existing evidence on the effectiveness of approaches to treating inclusion body myositis and to assess the methodological quality of this evidence. The Cochrane Controlled Trials Register (CENTRAL), Medline, Embase, Cinahl, Physiotherapy Evidence (Pedro), McMaster and Web of Science databases were searched. The references of identified articles and reviews were also checked for relevancy. The methodological quality was assessed according to the Cochrane Collaboration's domain-based evaluation framework. Of the 331 identified records, 10 were considered relevant for a qualitative analysis. The risk of bias was considered being low for six studies and high for four. Eight studies were randomized controlled trials, and two were controlled clinical trials. In the samples, male gender predominated, and the mean age of the participants varied from 51 to 72 years. The duration of intervention varied from 3 to 17 months. One small trial on the effect of oxandrolone reported a significant positive result. The other trials observed no improvement or insignificant improvement among the participants treated with intravenous immunoglobulin, methotrexate, etanercept or interferon. Thus far, there is no evidence indicating that any specific treatment is the effective in treating inclusion body myositis.

Targeted Molecular Therapies for SBMA

Spinal and bulbar muscular atrophy (SBMA) is a late-onset neuromuscular disease caused by a polyglutamine expansion in the androgen receptor gene which results in progressive spinal and bulbar motor neuron degeneration, and muscle atrophy. Although the causative genetic defect is known, until recently, the molecular pathogenesis of the disease was unclear, resulting in few, if any, targets for therapy development. However, over the past decade, our understanding of the pathomechanisms that play a role in SBMA has increased dramatically, and several of these pathways and mechanisms have now been investigated as possible therapeutic targets. In this review, we discuss some of the key pathomechanisms implicated in SBMA and describe some of the therapeutic strategies that have been tested in SBMA to date, which fall into four main categories: (i) gene silencing; (ii) protein quality control and/or increased protein degradation; (iii) androgen deprivation; and (iv) modulation of AR function. Finally, it is also now clear that in addition to a greater understanding of the molecular mechanisms that underlie disease, the development of an effective disease modifying therapy for SBMA will require the coordinated, collaborative effort of research teams with diverse areas of expertise, clinicians, pharmaceutical companies as well as patient groups.

The Role of the Protein Quality Control System in SBMA

Spinal and bulbar muscular atrophy (SBMA) or Kennedy's disease is an X-linked disease associated with the expansion of the CAG triplet repeat present in exon 1 of the androgen receptor (AR) gene. This results in the production of a mutant AR containing an elongated polyglutamine tract (polyQ) in its N-terminus. Interestingly, the ARpolyQ becomes toxic only after its activation by the natural androgenic ligands, possibly because of aberrant androgen-induced conformational changes of the ARpolyQ, which generate misfolded species. These misfolded ARpolyQ species must be cleared from motoneurons and muscle cells, and this process is mediated by the protein quality control (PQC) system. Experimental evidence suggested that failure of the PQC pathways occurs in disease, leading to ARpolyQ accumulation and toxicity in the target cells. In this review, we summarized the overall impact of mutant and misfolded ARpolyQ on the PQC system and described how molecular chaperones and the degradative pathways (ubiquitin-proteasome system (UPS), the autophagy-lysosome pathway (ALP), and the unfolded protein response (UPR), which activates the endoplasmic reticulum-associated degradation (ERAD)) are differentially affected in SBMA. We also extensively and critically reviewed several molecular and pharmacological approaches proposed to restore a global intracellular activity of the PQC system. Collectively, these data suggest that the fine and delicate equilibrium existing among the different players of the PQC system could be restored in a therapeutic perspective by the synergic/additive activities of compounds designed to tackle sequential or alternative steps of the intracellular defense mechanisms triggered against proteotoxic misfolded species.

BACE-1, PS-1 and sAPPβ Levels Are Increased in Plasma from Sporadic Inclusion Body Myositis Patients: Surrogate Biomarkers among Inflammatory Myopathies

Sporadic inclusion body myositis (sIBM) is a rare disease that is difficult to diagnose. Muscle biopsy provides three prominent pathological findings: inflammation, mitochondrial abnormalities and fibber degeneration, represented by the accumulation of protein depots constituted by β-amyloid peptide, among others. We aim to perform a screening in plasma of circulating molecules related to the putative etiopathogenesis of sIBM to determine potential surrogate biomarkers for diagnosis. Plasma from 21 sIBM patients and 20 age- and gender-paired healthy controls were collected and stored at -80°C. An additional population of patients with non-sIBM inflammatory myopathies was also included (nine patients with dermatomyositis and five with polymyositis). Circulating levels of inflammatory cytokines (interleukin [IL]-6 and tumor necrosis factor [TNF]-α), mitochondrial-related molecules (free plasmatic mitochondrial DNA [mtDNA], fibroblast growth factor-21 [FGF-21] and coenzyme-Q10 [CoQ]) and amyloidogenic-related molecules (beta-secretase-1 [BACE-1], presenilin-1 [PS-1], and soluble Aβ precursor protein [sAPPβ]) were assessed with magnetic bead-based assays, real-time polymerase chain reaction, enzyme-linked immunosorbent assay (ELISA) and high-pressure liquid chromatography (HPLC). Despite remarkable trends toward altered plasmatic expression of inflammatory and mitochondrial molecules (increased IL-6, TNF-α, circulating mtDNA and FGF-21 levels and decreased content in CoQ), only amyloidogenic degenerative markers including BACE-1, PS-1 and sAPPβ levels were significantly increased in plasma from sIBM patients compared with controls and other patients with non-sIBM inflammatory myopathies (p < 0.05). Inflammatory, mitochondrial and amyloidogenic degeneration markers are altered in plasma of sIBM patients confirming their etiopathological implication in the disease. Sensitivity and specificity analysis show that BACE-1, PS-1 and sAPPβ represent a good predictive noninvasive tool for the diagnosis of sIBM, especially in distinguishing this disease from polymyositis.

An overview of muscle diseases presenting in adulthood

Patients with muscle disease present not only to neurologists, but also to rheumatologists and general physicians. This article provides a framework of how to approach patients with suspected muscle disease, and reviews the clinical features of the most frequently encountered acquired and genetic conditions in adult practice.

Treatment for inclusion body myositis

BACKGROUND

Inclusion body myositis (IBM) is a late-onset inflammatory muscle disease (myopathy) associated with progressive proximal and distal limb muscle atrophy and weakness. Treatment options have attempted to target inflammatory and atrophic features of this condition (for example with immunosuppressive and immunomodulating drugs, anabolic steroids, and antioxidant treatments), although as yet there is no known effective treatment for reversing or minimising the progression of inclusion body myositis. In this review we have considered the benefits, adverse effects, and costs of treatment in targeting cardinal effects of the condition, namely muscle atrophy, weakness, and functional impairment.

OBJECTIVES

To assess the effects of treatment for IBM.

SEARCH METHODS

On 7 October 2014 we searched the Cochrane Neuromuscular Disease Group Specialized Register, the Cochrane Central Register for Controlled Trials (CENTRAL), MEDLINE, and EMBASE. Additionally in November 2014 we searched clinical trials registries for ongoing or completed but unpublished trials.

SELECTION CRITERIA

We considered randomised or quasi-randomised trials, including cross-over trials, of treatment for IBM in adults compared to placebo or any other treatment for inclusion in the review. We specifically excluded people with familial IBM and hereditary inclusion body myopathy, but we included people who had connective tissue and autoimmune diseases associated with IBM, which may or may not be identified in trials. We did not include studies of exercise therapy or dysphagia management, which are topics of other Cochrane systematic reviews.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodological procedures.

MAIN RESULTS

The review included 10 trials (249 participants) using different treatment regimens. Seven of the 10 trials assessed single agents, and 3 assessed combined agents. Many of the studies did not present adequate data for the reporting of the primary outcome of the review, which was the percentage change in muscle strength score at six months. Pooled data from two trials of interferon beta-1a (n = 58) identified no important difference in normalised manual muscle strength sum scores from baseline to six months (mean difference (MD) -0.06, 95% CI -0.15 to 0.03) between IFN beta-1a and placebo (moderate-quality evidence). A single trial of methotrexate (MTX) (n = 44) provided moderate-quality evidence that MTX did not arrest or slow disease progression, based on reported percentage change in manual muscle strength sum scores at 12 months. None of the fully published trials were adequately powered to detect a treatment effect. We assessed six of the nine fully published trials as providing very low-quality evidence in relation to the primary outcome measure. Three trials (n = 78) compared intravenous immunoglobulin (combined in one trial with prednisone) to a placebo, but we were unable to perform meta-analysis because of variations in study analysis and presentation of trial data, with no access to the primary data for re-analysis. Other comparisons were also reported in single trials. An open trial of anti-T lymphocyte immunoglobulin (ATG) combined with MTX versus MTX provided very low-quality evidence in favour of the combined therapy, based on percentage change in quantitative muscle strength sum scores at 12 months (MD 12.50%, 95% CI 2.43 to 22.57). Data from trials of oxandrolone versus placebo, azathioprine (AZA) combined with MTX versus MTX, and arimoclomol versus placebo did not allow us to report either normalised or percentage change in muscle strength sum scores. A complete analysis of the effects of arimoclomol is pending data publication. Studies of simvastatin and bimagrumab (BYM338) are ongoing. All analysed trials reported adverse events. Only 1 of the 10 trials interpreted these for statistical significance. None of the trials included prespecified criteria for significant adverse events.

AUTHORS' CONCLUSIONS

Trials of interferon beta-1a and MTX provided moderate-quality evidence of having no effect on the progression of IBM. Overall trial design limitations including risk of bias, low numbers of participants, and short duration make it difficult to say whether or not any of the drug treatments included in this review were effective. An open trial of ATG combined with MTX versus MTX provided very low-quality evidence in favour of the combined therapy based on the percentage change data given. We were unable to draw conclusions from trials of IVIg, oxandrolone, and AZA plus MTX versus MTX. We need more randomised controlled trials that are larger, of longer duration, and that use fully validated, standardised, and responsive outcome measures.

Sporadic inclusion body myositis: new insights and potential therapy

PURPOSE OF THE REVIEW

To describe new insights and developments in the pathogenesis, diagnosis and treatment of sporadic inclusion body myositis (IBM).

RECENT FINDINGS

Various hypothesis about the pathogenesis of IBM continue to be investigated, including autoimmune factors, mitochondrial dysfunction, protein dyshomeostasis, altered nucleic acid metabolism, myonuclear degeneration and the role of the myostatin pathway. Serum autoantibodies against cytosolic 5'-nucleotidase 1A have been identified in IBM showing moderate diagnostic performance. The differential diagnostic value of histopathological features, including different protein aggregates, continues to be evaluated. MRI may also be of monitoring value in IBM. New therapeutic strategies are being tested in IBM patients, namely the upregulation of the heat shock response and the antagonism of myostatin.

SUMMARY

Recent important advances have occurred in IBM. These advances, including recent and ongoing clinical trials, may lead to earlier diagnosis and improved understanding and treatment of the disease. Despite improved knowledge, IBM continues to be a puzzling disease and the pathogenesis remains to be clarified. An interdisciplinary, bench to bedside translational research approach is crucial for the successful identification of novel treatments for this debilitating, currently untreatable disorder.

Clinical values of FDG PET in polymyositis and dermatomyositis syndromes: imaging of skeletal muscle inflammation

OBJECTIVES

[(18)F] Fluorodeoxyglucose positron emission tomography (FDG PET), a standard tool for evaluating malignancies, can also detect inflammatory lesions. However, its usefulness in evaluating muscle lesions in polymyositis and dermatomyositis syndromes (PM/DM) has not been established.

METHODS

33 patients with PM/DM who had undergone FDG PET were retrospectively analysed. FDG uptake was visually evaluated (visually identified FDG uptake, vFDG) in 16 regions of the body using mediastinum blood vessels as a positivity criterion. We also calculated the maximum standardised uptake value (SUVmax) in all four limbs of the patients with PM/DM as well as in 22 patients with amyotrophic lateral sclerosis (ALS) with similar disabilities. In 24 patients with PM/DM, MRI and FDG PET findings were compared.

RESULTS

vFDG was observed in multiple muscle lesions with varying distributions in two-thirds of the patients with PM/DM, with most lesions being symmetrical. The number of vFDG-positive regions strongly correlated with the mean SUVmax in all four limbs (p<0.0001). Histological grades of biopsied muscles correlated with both the mean SUVmax and number of vFDG-positive regions. Serum creatine kinase levels were higher in patients with more than two vFDG-positive regions than in those with two or less regions (p<0.05). While the inflamed muscles showed diffused, patchy or marginal signal abnormalities on MRI, FDG uptake was most prominent inside the muscles. Compared with ALS, the mean SUVmax was significantly higher in the patients with PM/DM (p<0.0001) and showed a striking correlation in the bilateral muscles, reflecting symmetrical muscle involvement in PM/DM.

CONCLUSIONS

The visual assessment of FDG uptake as well as calculation of SUV enabled us to comprehensively evaluate skeletal muscle. This method can improve clinical practices and provide insights into pathomechanisms of PM/DM.

Ongoing developments in sporadic inclusion body myositis

Sporadic inclusion body myositis (IBM) is an acquired muscle disorder associated with ageing, for which there is no effective treatment. Ongoing developments include: genetic studies that may provide insights regarding the pathogenesis of IBM, improved histopathological markers, the description of a new IBM autoantibody, scrutiny of the diagnostic utility of clinical features and biomarkers, the refinement of diagnostic criteria, the emerging use of MRI as a diagnostic and monitoring tool, and new pathogenic insights that have led to novel therapeutic approaches being trialled for IBM, including treatments with the objective of restoring protein homeostasis and myostatin blockers. The effect of exercise in IBM continues to be investigated. However, despite these ongoing developments, the aetiopathogenesis of IBM remains uncertain. A translational and multidisciplinary collaborative approach is critical to improve the diagnosis, treatment, and care of patients with IBM.

Sporadic inclusion body myositis: the genetic contributions to the pathogenesis

Sporadic inclusion body myositis (sIBM) is the commonest idiopathic inflammatory muscle disease in people over 50 years old. It is characterized by slowly progressive muscle weakness and atrophy, with typical pathological changes of inflammation, degeneration and mitochondrial abnormality in affected muscle fibres. The cause(s) of sIBM are still unknown, but are considered complex, with the contribution of multiple factors such as environmental triggers, ageing and genetic susceptibility. This review summarizes the current understanding of the genetic contributions to sIBM and provides some insights for future research in this mysterious disease with the advantage of the rapid development of advanced genetic technology. An international sIBM genetic study is ongoing and whole-exome sequencing will be applied in a large cohort of sIBM patients with the aim of unravelling important genetic risk factors for sIBM.

Inclusion body myositis

The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of rare disorders that share many similarities. In addition to sporadic inclusion body myositis (IBM), these include dermatomyositis, polymyositis, and autoimmune necrotizing myopathy. IBM is the most common IIM after age 50 years. Muscle histopathology shows endomysial inflammatory exudates surrounding and invading nonnecrotic muscle fibers often accompanied by rimmed vacuoles and protein deposits. It is likely that IBM is has a prominent degenerative component. This article reviews the evolution of knowledge in IBM, with emphasis on recent developments in the field, and discusses ongoing clinical trials.

Are we closer to having drugs to treat muscle wasting disease?

The two most common muscle wasting diseases in adults are sarcopenia and cachexia. Despite differences in their pathophysiology, it is believed that both conditions are likely to respond to drugs that increase muscle mass and muscle strength. The current gold standard in this regard is exercise training. This article provides an overview of candidate drugs to treat muscle wasting disease that are available or in development. Drugs highlighted here include ghrelin agonists, selective androgen receptor molecules, megestrol acetate, activin receptor antagonists, espindolol, and fast skeletal muscle troponin inhibitors.