Inclusion body myositis: clinical and histopathological features of 36 patients

Treatment resistance in inclusion body myositis: the role of mast cells

Inclusion body myositis is the commonest acquired myopathy in those over 50 years of age. Although it is classified as an idiopathic inflammatory myopathy and the most frequent finding on muscle biopsy in inclusion body myositis is an endomysial inflammatory infiltrate, it is clinically distinct from other myositis, including a lack of response to immunosuppressive medication. Neurogenic changes are commonly reported in inclusion body myositis and inflammatory changes are observed in muscle following neurogenic injury. The objective of our study was to explore whether neurogenic inflammation plays a role in the pathogenesis of inclusion body myositis, possibly explaining its resistance to immunosuppression. The number of mast cells and presence of neuropeptides, substance P and calcitonin gene-related peptide, were assessed in 48 cases of inclusion body myositis, 11 cases of steroid responsive myositis, two cases of focal myositis associated with neurogenic injury, and ten normal controls. The number of mast cells in inclusion body myositis focal and myositis associated to neurogenic injury were significantly greater than that observed in steroid responsive myositis. Our findings suggest that neurogenic inflammation mediated through mast cells may play a role in the pathogenesis of inclusion body myositis, and focal myositis associated to neurogenic injury, and thus, explain in some part its lack of response to immunosuppressive treatments.

Sporadic Inclusion Body Myositis at the Crossroads between Muscle Degeneration, Inflammation, and Aging

Sporadic inclusion body myositis (sIBM) is the most common muscle disease of older people and is clinically characterized by slowly progressive asymmetrical muscle weakness, predominantly affecting the quadriceps, deep finger flexors, and foot extensors. At present, there are no enduring treatments for this relentless disease that eventually leads to severe disability and wheelchair dependency. Although sIBM is considered a rare muscle disorder, its prevalence is certainly higher as the disease is often undiagnosed or misdiagnosed. The histopathological phenotype of sIBM muscle biopsy includes muscle fiber degeneration and endomysial lymphocytic infiltrates that mainly consist of cytotoxic CD8+ T cells surrounding nonnecrotic muscle fibers expressing MHCI. Muscle fiber degeneration is characterized by vacuolization and the accumulation of congophilic misfolded multi-protein aggregates, mainly in their non-vacuolated cytoplasm. Many players have been identified in sIBM pathogenesis, including environmental factors, autoimmunity, abnormalities of protein transcription and processing, the accumulation of several toxic proteins, the impairment of autophagy and the ubiquitin-proteasome system, oxidative and nitrative stress, endoplasmic reticulum stress, myonuclear degeneration, and mitochondrial dysfunction. Aging has also been proposed as a contributor to the disease. However, the interplay between these processes and the primary event that leads to the coexistence of autoimmune and degenerative changes is still under debate. Here, we outline our current understanding of disease pathogenesis, focusing on degenerative mechanisms, and discuss the possible involvement of aging.

Clinical Subgroups and Factors Associated With Progression in Patients With Inclusion Body Myositis

BACKGROUND AND OBJECTIVES

Sporadic inclusion body myositis (IBM) is the most common acquired myopathy in individuals older than 50 years. The disorder is slowly progressive, and although many therapies have been investigated, response has generally been poor. Clinical heterogeneity may influence treatment responsiveness; however, data regarding heterogeneity in IBM are limited and often conflicting. We aim to identify clinically distinct subgroups within a large IBM cohort and prognostic factors for disease progression.

METHODS

Clinical, histologic, radiologic, and electrophysiologic data were analyzed for all patients with IBM and other forms of myositis enrolled in a longitudinal cohort from The Johns Hopkins Myositis Center from 2003 to 2018. Patients with IBM were included if they met at least one of the following criteria: Griggs possible, European Neuromuscular Centre 2011 probable, or Lloyd-Greenberg data-derived criteria for IBM. Univariate, multivariate, and graphical analyses were used to identify prognostic factors in patients with IBM. Thus, linear and logistic regressions were used to adjust for potential confounding variables. The evolution of creatine kinase and muscle strength was studied using multilevel linear regression models. Nonmodifiable risk factors (sex, race, disease duration, and age at the onset of first symptoms) were used as adjusting covariates for the regression analyses.

RESULTS

Among the 335 patients meeting the inclusion criteria for IBM, 64% were male with an average age of disease onset of 58.7 years and delay to diagnosis of 5.2 years. Initial misdiagnosis (52%) and immunosuppressant treatment (42%) were common. Less than half (43%) of muscle biopsies demonstrated all 3 pathologic hallmarks: endomysial inflammation, mononuclear cell invasion, and rimmed vacuoles. Black patients had significantly weaker arm abductors, hip flexors, and knee flexors compared with non-Black patients. Female patients had stronger finger flexors and knee extensors compared with their male counterparts. Younger age (<50 years) at onset was not associated with increased weakness.

DISCUSSION

Our study demonstrates that female and Black patients have distinct clinical phenotypes and trajectories within the overarching IBM clinical phenotype. These subgroups may have different responses to therapies, which may influence the design of future clinical trials in IBM.

Clinical implication of denervation in sporadic inclusion body myositis

INTRODUCTION

Sporadic inclusion body myositis (sIBM) is often accompanied by signs suggestive of denervation on electromyography (EMG), which mimics neurogenic disorders. Hence, the current study aimed to assess reinnervation after denervation in sIBM and its clinical impllcation.

METHODS

We retrospectively examined consecutive muscle biopsy specimens collected from 109 sIBM patients who were referred to our institution for diagnostic muscle biopsy from 2001 to 2018. Reinnervation after denervation in sIBM patients was assessed via muscle biopsy and EMG. The levels of acetylcholine receptor subunit γ (Chrng) and muscle-specific kinase (MuSK) mRNA, which are markers of denervation, were examined using real-time polymerase chain reaction. Response to treatment was defined as an increase of grade 1 or higher in two or more muscle groups as assessed using the Medical Research Council scale.

RESULTS

In total, 93 (85.3%) of 109 sIBM patients had reinnervation after denervation on histological examination and/or EMG. The mean disease duration before biopsy was significantly longer in patients with reinnervation after denervation than in those without (p < 0.00001). Patients with denervation had significantly higher levels of Chrng and MuSK mRNA than those without. The proportion of patients who responded to immunosuppressive therapies was smaller in the patients with denervation than those without (p < 0.05). However, there was no significant difference regarding time from onset to using a walking aid between the two groups.

DISCUSSION

Reinnervation after denervation is associated with disease duration and short-term response to therapy in individuals with sIBM.

Diagnostic Accuracy of Anti-CN1A on the Diagnosis of Inclusion Body Myositis. A Hierarchical Bivariate and Bayesian Meta-analysis

ABSTRACT

Sporadic inclusion body myositis (IBM) is an acquired muscle disease and the most common idiopathic inflammatory myopathy over the age of 50. It is characterized by male predominance, with a prevalence rate between 1 and 71 cases per million, reaching 139 cases per million over the age of 50 globally. The diagnosis of IBM is based on clinical presentation and muscle biopsy findings. However, there is increasing evidence for the role of genetics and serum biomarkers in supporting a diagnosis. Antibodies against the cytosolic 5'-nucleotidase 1A (Anti-CN1A), an enzyme catalyzing the conversion of adenosine monophosphate into adenosine and phosphate and is abundant in skeletal muscle, has been reported to be present in IBM and could be of crucial significance in the diagnosis of the disease. In this study, we investigated the diagnostic accuracy of anti-CN1A antibodies for sporadic IBM in comparison with other inflammatory myopathies, autoimmune disorders, motor neurone disease, using a hierarchical bivariate approach, and a Bayesian model taking into account the variable prevalence. The results of the present analysis show that anti-CN1A antibodies have moderate sensitivity, and despite having high specificity, they are not useful biomarkers for the diagnosis of IBM, polymyositis or dermatomyositis, other autoimmune conditions, or neuromuscular disorders. Neither the hierarchical bivariate nor the Bayesian analysis showed any significant usefulness of anti-CN1A antibodies in the diagnosis of IBM.

Diagnostic criteria for inclusion body myositis

Inclusion body myositis (IBM) was first identified as a specific disorder about 40 years ago and is now recognized to be the most frequently presenting primary myopathy in middle age and beyond. Initial characterization was based on the observation of specific pathological features distinguishing it from polymyositis. It was soon appreciated that there were also distinguishing clinical features. The earliest diagnostic criteria were heavily biased towards pathological features, but over time revised criteria have given increasing importance to certain clinical features. Until the specific cause of IBM is determined, and the basic pathogenetic mechanisms are better understood, there can be no diagnostic gold-standard against which to compare the sensitivity and specificity of any proposed diagnostic criteria, but such criteria are essential to ensure that patients entering clinical, epidemiological, genetic, pathological or therapeutic studies represent a homogeneous population. It is likely that any currently accepted diagnostic criteria will, once a gold-standard is eventually established, be shown to have 'missed' patients with atypical features, but that has to be accepted to make certain that current studies are not contaminated by patients who do not have IBM. In other words, in everyday clinical practice there will be the occasional patient who an experienced myologist strongly suspects has IBM, but does not meet current criteria - the criteria lack sensitivity. But if the criteria are so broad as to include all such atypical cases, they would be likely to include patients who do not in fact have IBM - they would lack specificity. The sensitivity and specificity of existing criteria have been reviewed recently, in so far as it is possible to do so, and found to have high specificity but variable sensitivity.

Sporadic inclusion body myositis: A review of recent clinical advances and current approaches to diagnosis and treatment

Sporadic inclusion body myositis is the most frequent acquired myopathy of middle and later life and is distinguished from other inflammatory myopathies by its selective pattern of muscle involvement and slowly progressive course, and by the combination of inflammatory and degenerative muscle pathology and multi-protein deposits in muscle tissue. This review summarises the findings of recent studies that provide a more complete picture of the clinical phenotype and natural history of the disease and its global prevalence and genetic predisposition. Current diagnostic criteria, including the role of electrophysiological and muscle imaging studies and the recently identified anti-5'-nucleotidase (anti-cN1A) antibody in diagnosis are also discussed as well as current trends in the treatment of the disease.

Clinical assessment determines the diagnosis of inclusion body myositis independently of pathological features

BACKGROUND AND OBJECTIVE

Historically, the diagnosis of sporadic inclusion body myositis (IBM) has required the demonstration of the presence of a number of histopathological findings on muscle biopsy--namely, rimmed vacuoles, an inflammatory infiltrate with invasion of non-necrotic muscle fibres (partial invasion) and amyloid or 15-18 nm tubulofilamentous inclusions (Griggs criteria). However, biopsies of many patients with clinically typical IBM do not show all of these histopathological findings, at least at presentation. We compared the clinical features at presentation and during the course of disease in 67 patients with histopathologically diagnosed IBM and clinically diagnosed IBM seen within a single UK specialist muscle centre.

METHODS AND RESULTS

At presentation, using clinically focused diagnostic criteria (European Neuromuscular Centre (ENMC) 2011), a diagnosis of IBM was made in 88% of patients whereas 76% fulfilled the 1997 ENMC criteria and only 27% satisfied the histopathologically focused Griggs criteria. There were no differences in clinical features or outcomes between clinically and histopathologically diagnosed patients, but patients lacking the classical histopathological finding of rimmed vacuoles were younger, suggesting that rimmed vacuoles may be a later feature of the disease.

CONCLUSIONS

These findings have important implications for diagnosis and future studies or trials in IBM as adherence to histopathologically focused diagnostic criteria will exclude large numbers of patients with IBM. Importantly, those excluded may be at an earlier stage of the disease and more amenable to treatment.

Inclusion body myositis: therapeutic approaches

The idiopathic inflammatory myopathies are a heterogeneous group of diseases that include dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM) and other less common myopathies. These are clinically and histopathologically distinct diseases with many shared clinical features. IBM, the most commonly acquired inflammatory muscle disease occurs in individuals aged over 50 years, and is characterized by slowly progressive muscle weakness and atrophy affecting proximal and distal muscle groups, often asymmetrically. Unlike DM and PM, IBM is typically refractory to immunotherapy. Although corticosteroids have not been tested in randomized controlled trials, the general consensus is that they are not efficacious. There is some suggestion that intravenous immunoglobulin slows disease progression, but its long-term effectiveness is unclear. The evidence for other immunosuppressive therapies has been derived mainly from case reports and open studies and the results are discouraging. Only a few clinical trials have been conducted on IBM, making it difficult to provide clear recommendations for treatment. Moreover, IBM is a slowly progressive disease so assessment of treatment efficacy is problematic due to the longer-duration trials needed to determine treatment effects. Newer therapies may be promising, but further investigation to document efficacy would be expensive given the aforementioned need for longer trials. In this review, various treatments that have been employed in IBM will be discussed even though none of the interventions has sufficient evidence to support its routine use.

Long-term observational study of sporadic inclusion body myositis

We describe a long-term observational study of a large cohort of patients with sporadic inclusion body myositis and propose a sporadic inclusion body myositis weakness composite index that is easy to perform during a clinic. Data collection from two groups of patients (Paris and Oxford) was completed either during a clinic visit (52%), or by extraction from previous medical records (48%). One hundred and thirty-six patients [57% males, 61 (interquartile range 55-69) years at onset] were included. At the last visit all patients had muscle weakness (proximal British Medical Research Council scale <3/5 in 48%, distal British Medical Research Council scale <3/5 in 40%, swallowing problems in 46%). During their follow-up, 75% of patients had significant walking difficulties and 37% used a wheelchair (after a median duration from onset of 14 years). The sporadic inclusion body myositis weakness composite index, which correlated with grip strength (correlation coefficient: 0.47; P < 0.001) and Rivermead Mobility Index (correlation coefficient: 0.85; P < 0.001), decreased significantly with disease duration (correlation coefficient: -0.47; P < 0.001). The risk of death was only influenced by older age at onset of first symptoms. Seventy-one (52%) patients received immunosuppressive treatments [prednisone in 91.5%, associated (in 64.8%) with other immunomodulatory drugs (intravenous immunoglobulins, methotrexate or azathioprine) for a median duration of 40.8 months]. At the last assessment, patients who had been treated were more severely affected on disability scales (Walton P = 0.007, Rivermead Mobility Index P = 0.004) and on the sporadic inclusion body myositis weakness composite index (P = 0.04). The first stage of disease progression towards handicap for walking was more rapid among patients receiving immunosuppressive treatments (hazard ratio = 2.0, P = 0.002). This study confirms that sporadic inclusion body myositis is slowly progressive but not lethal and that immunosuppressive treatments do not ameliorate its natural course, thus confirming findings from smaller studies. Furthermore, our findings suggest that immunosuppressant drug therapy could have modestly exacerbated progression of disability. The sporadic inclusion body myositis weakness composite index might be a valuable outcome measure for future clinical trials, but requires further assessment and validation.

Gait patterns of patients with inclusion body myositis

Inclusion body myositis (IBM) is a progressive, inflammatory muscle disease that is known to cause quadriceps weakness and knee buckling during gait. This is the first known report of gait characteristics in patients with IBM. Nine subjects with IBM and quadriceps weakness underwent gait analysis and quantitative strength testing. A wide range of strength and gait abilities were present in the subject group. Subjects with stronger knee extensors exhibited nearly normal sagittal knee kinematics and kinetics. As quadriceps strength decreased, kinematic and kinetic patterns were increasingly abnormal. Exceptions to this pattern could be explained by examining strength at adjacent joints. Gait analysis and strength testing is a helpful tool in evaluating the functional status of this population and aiding in determination of the needs for interventions such as assistive devices.

How citation distortions create unfounded authority: analysis of a citation network

OBJECTIVE

To understand belief in a specific scientific claim by studying the pattern of citations among papers stating it.

DESIGN

A complete citation network was constructed from all PubMed indexed English literature papers addressing the belief that beta amyloid, a protein accumulated in the brain in Alzheimer's disease, is produced by and injures skeletal muscle of patients with inclusion body myositis. Social network theory and graph theory were used to analyse this network.

MAIN OUTCOME MEASURES

Citation bias, amplification, and invention, and their effects on determining authority.

RESULTS

The network contained 242 papers and 675 citations addressing the belief, with 220,553 citation paths supporting it. Unfounded authority was established by citation bias against papers that refuted or weakened the belief; amplification, the marked expansion of the belief system by papers presenting no data addressing it; and forms of invention such as the conversion of hypothesis into fact through citation alone. Extension of this network into text within grants funded by the National Institutes of Health and obtained through the Freedom of Information Act showed the same phenomena present and sometimes used to justify requests for funding.

CONCLUSION

Citation is both an impartial scholarly method and a powerful form of social communication. Through distortions in its social use that include bias, amplification, and invention, citation can be used to generate information cascades resulting in unfounded authority of claims. Construction and analysis of a claim specific citation network may clarify the nature of a published belief system and expose distorted methods of social citation.

Genetically augmenting Abeta42 levels in skeletal muscle exacerbates inclusion body myositis-like pathology and motor deficits in transgenic mice

The pathogenic basis of inclusion body myositis (IBM), the leading muscle degenerative disease afflicting the elderly, is unknown, although the histopathological features are remarkably similar to those observed in Alzheimer's disease. One leading hypothesis is that the buildup of amyloid-beta (Abeta) peptide within selective skeletal muscle fibers contributes to the degenerative phenotype. Abeta is a small peptide derived via endoproteolysis of the amyloid precursor protein (APP). To determine the pathogenic effect of augmenting Abeta42 levels in skeletal muscle, we used a genetic approach to replace the endogenous wild-type presenilin-1 (PS1) allele with the PS1(M146V) allele in MCK-APP mice. Although APP transgene expression was unaltered, Abeta levels, particularly Abeta42, were elevated in skeletal muscle of the double transgenic (MCK-APP/PS1) mice compared to the parental MCK-APP line. Elevated phospho-tau accumulation was found in the MCK-APP/PS1 mice, and the greater activation of GSK-3beta and cdk5 were observed. Other IBM-like pathological features, such as inclusion bodies and inflammatory infiltrates, were more severe and prominent in the MCK-APP/PS1 mice. Motor coordination and balance were more adversely affected and manifested at an earlier age in the MCK-APP/PS1 mice. The data presented here provide experimental evidence that Abeta42 plays a proximal and critical role in the muscle degenerative process.

Inclusion body myositis

The clinical features of inclusion body myositis (IBM) were of minor importance in the design of consensus diagnostic criteria, mainly because of controversial views on the specificity of signs and symptoms, although some authors reported "typical" signs. To re-assess the clinical spectrum of IBM, a single investigator using a standard protocol studied a cohort of 64 patients cross-sectionally. Symptom onset was before the age of 50 years in 20% of cases. Only a few patients (14 %) started with weakness other than that of quadriceps, finger flexor or pharyngeal muscles. The sequence of power loss was erratic, but onset of symptoms with quadriceps weakness predicted an earlier onset of dysphagia in older patients (> or = 56 years) compared with younger ones (< 56 years) (p = 0.02). Despite widespread weakness patients had favourable scores on three commonly used function scales and they kept their employment. Complete wheel-chair dependency was rare (3 %). A dominant characteristic was the anatomical distribution of afflicted muscles: ventral extremity muscle groups were more affected than dorsal muscle groups and girdle muscles were least affected, the latter preserving postural stability. Ankylosis, especially in extension of the fingers,was frequently present. Together with the sparing of intrinsic hand muscles it was helpful in the preservation of many skillful movements. IBM has a unique distribution of muscle weakness. Ankylotic contractures are common. We feel that their joint impact on daily functioning is characteristic for the disease.

Patterns of muscle involvement in inclusion body myositis: clinical and magnetic resonance imaging study

The differential patterns of muscle involvement in the upper and lower limbs in sporadic inclusion body myositis (sIBM) were examined in 18 patients using both quantitative and manual muscle testing as well as magnetic resonance imaging (MRI) in 9 patients. Weakness of the quadriceps femoris and the forearm flexors was present in most patients, but there was considerable variability in the patterns and severity of muscle involvement. MRI disclosed preferential patterns of muscle involvement within functional groups such as the quadriceps femoris, in which there was severe involvement of the vasti with relative sparing of the rectus femoris, and the triceps surae, in which selective involvement of the medial gastrocnemius was common. Involvement of flexor digitorum profundus on MRI was found in only one third of patients. The results emphasize the variability in the clinical phenotype and differential susceptibility of muscles to the disease process in sIBM.

Macrophagic myofasciitis associated with inclusion body myositis: a report of three cases

We describe three patients with macrophagic myofasciitis and inclusion body myositis. All patients fulfilled diagnostic criteria for inclusion body myositis and myopathologic criteria for macrophagic myofasciitis. In the three cases macrophagic myofasciitis complicated the evolution of a known and painless inclusion body myositis and was diagnosed in a repeated deltoid biopsy because of the appearance of myalgia during the course of inclusion body myositis in all cases. The unexpected appearance of myalgia during the course of painless inclusion body myositis must arouse the suspicion of an association of another inflammatory muscle disease, macrophagic myofasciitis.

Clinical, serologic, and immunogenetic features of familial idiopathic inflammatory myopathy

OBJECTIVE

To describe the clinical, serologic, and immunogenetic features of familial idiopathic inflammatory myopathy (IIM) and to compare these with the features of sporadic IIM.

METHODS

Clinical signs and symptoms, autoantibodies, HLA-DRB1 and DQA1 alleles, and GM/KM phenotypes were compared among 36 affected and 28 unaffected members of 16 unrelated families in which 2 or more blood relatives developed an IIM. In addition, findings in patients with familial IIM were compared with those in 181 patients with sporadic IIM. The families included 3 pairs of monozygotic twins with juvenile dermatomyositis, 11 families with other siblings or relatives with polymyositis or dermatomyositis, and 2 families with inclusion body myositis.

RESULTS

The clinical features of familial IIM were similar to those of sporadic IIM, although the frequency of myositis-specific autoantibodies was lower in familial than in sporadic IIM. DRB1*0301 was a common genetic risk factor for familial and sporadic IIM, but contributed less to the genetic risk of familial IIM (etiologic fraction 0.35 versus 0.51 in sporadic IIM). Homozygosity at the HLA-DQA1 locus was found to be a genetic risk factor unique to familial IIM (57% versus 24% of controls; odds ratio 4.2, corrected P = 0.002).

CONCLUSION

These findings emphasize that 1) familial muscle weakness is not always due to inherited metabolic defects or dystrophies, but may be the result of the development of IIM in several members of the same family, and 2) multiple genetic factors are likely important in the etiology and disease expression of familial IIM, as is also the case for sporadic myositis, but DQA1 homozygosity is a distinct risk factor for familial IIM.

Immune-mediated conditions and antibodies associated with sporadic inclusion body myositis

We reviewed 99 patients with sporadic inclusion body myositis (IBM), searching for a coexisting autoimmune disease, other conditions with altered immune function, or the presence of autoantibodies. Thirteen patients had one or more of 11 diseases with altered immune function. Forty-three patients had elevated titers of one or more of nine different, albeit nondisease-specific, autoantibodies. Twenty-five patients had dysproteinemia or dysproteinuria. We conclude that IBM is frequently associated with systemic immune disorders or nonspecific autoantibodies. Although aging may explain some of these phenomena, an altered immune function need to be considered in the pathogenesis of IBM.

Congenital myopathy in Braunvieh x Brown Swiss calves

A hitherto unknown skeletal muscle disorder is described in six Braunvieh x Brown Swiss calves. The animals showed rapidly progressing muscular weakness and became recumbent within 2 weeks of birth. Histological examination of skeletal muscle revealed a marked variation in muscle fibre size, internally placed nuclei, segmental loss of cross-striation with disorganization of myofibrils, and accumulation of nemaline rods. The most distinctive histological finding was intracytoplasmic, homogeneous, mostly crescent-shaped areas at the periphery of numerous muscle fibres. Electron microscopically, accumulations of tightly packed, parallel filamentous structures, about 20 nm in diameter, were detected in these areas. Enzyme histochemistry showed that all muscle fibre types were affected. Vimentin and dystrophin immunohistochemistry revealed normal antigen distribution within connective tissue components and at the periphery of each muscle fibre, respectively. The lesions could be readily distinguished from other neurological and neuromuscular disorders previously described in Braunvieh x Brown Swiss or American Brown Swiss Cattle. The disease appears to be a novel congenital myopathy in this breed, and a hereditary aetiology is suspected.