A 63-Year-Old Man Presents With Slowly Progressive Dyspnea on Exertion and Lower Extremity Muscle Weakness

CASE PRESENTATION

A 63-year-old man was referred for slowly progressive dyspnea on exertion that had developed over 7 years. Dyspnea was initially only present during high-intensity physical activity, but was now present while walking rapidly on a flat surface. Symptoms were accentuated while supine and when bending forward. He reported respiratory difficulties when submerged in water and a recent onset of slight symmetric lower limb weakness that was only apparent during strenuous physical activity. He also had OSA, which was adequately controlled with continuous positive airway pressure therapy. Neurologic and rheumatologic histories were otherwise unremarkable. He denied any impact accidents or trauma to the cervical spine and prior neck or thoracic surgeries.

Clinical and Electrophysiological Findings in Hereditary Inclusion Body Myopathy Compared With Sporadic Inclusion Body Myositis

OBJECTIVE

To compare the clinical and electrophysiological findings in hereditary inclusion body myopathy (hIBM) and sporadic inclusion body myositis (sIBM) patients.

METHODS

We retrospectively identified 8 genetically proven hIBM patients and 1 DNAJB6 myopathy with pathological features of hIBM, and compared their clinical, electromyographic, and serological data with a group of 51 pathologically proven sIBM patients.

RESULTS

hIBM patients had a younger mean age of onset (36 vs. 60 years, P = 0.0001). Diagnostic delay was shorter in sIBM (6 vs. 15 years, P = 0.0003). Wrist flexors (P = 0.02), digit flexors (P = 0.01), digit extensors (P = 0.02), and quadriceps (P = 0.008) muscles were more frequently affected in sIBM. Fibrillation potentials were more common in sIBM patients (P = 0.03). Electrical myotonia was found in 4 hIBM patients, not significantly different from sIBM patients (P = 0.45). Creatinine kinase was higher in sIBM patients (799 vs 232, P = 0.03).

CONCLUSIONS

sIBM and hIBM seem to have similar electromyographic changes. The combination of clinical, serological, and histopathological findings can guide genetic testing to the final diagnosis.

Sporadic Inclusion Body Myositis Manifesting as Isolated Muscle Weakness of the Finger Flexors Three Years after Disease Onset

Sporadic inclusion body myositis (sIBM) is a chronic progressive myopathy characterized by muscle weakness of both the quadriceps femoris and finger flexors. We herein present the case of a typical male patient with sIBM, which manifested as the isolated weakness of the finger flexors three years after the disease onset. We have identified several patients with sIBM in our cohort with muscle weakness of the flexors but not the quadriceps femoris. Examination of the flexor digitorum profundus muscle is important for the early and proper diagnosis of sIBM, even if a patient only presents with isolated finger flexor muscle weakness.

HMGB1 and RAGE in skeletal muscle inflammation: Implications for protein accumulation in inclusion body myositis

Inflammation is associated with protein accumulation in IBM, but precise mechanisms are elusive. The "alarmin" HMGB1 is upregulated in muscle inflammation. Its receptor RAGE is crucial for β-amyloid-associated neurodegeneration. Relevant signaling via HMGB1/RAGE is expected in IBM pathology. By real-time-PCR, mRNA-expression levels of HMGB1 and RAGE were upregulated in muscle biopsies of patients with IBM and PM, but not in muscular dystrophy or non-myopathic controls. By immunohistochemistry, both molecules displayed the highest signal in IBM, where they distinctly co-localized to intra-fiber accumulations of β-amyloid and neurofilament/tau. In these fibers, identification of phosphorylated Erk suggested that relevant downstream activation is present upon HMGB1 signaling via RAGE. Protein expressions of HMGB1, RAGE, Erk and phosphorylated Erk were confirmed by Western blot. In a well established cell-culture model for pro-inflammatory cell-stress, exposure of human muscle-cells to IL-1β+IFN-γ induced cytoplasmic translocation of HMGB1 and subsequent release as evidenced by ELISA. Upregulation of RAGE on the cell surface was demonstrated by immunocytochemistry and flow-cytometry. Recombinant HMGB1 was equally potent as IL-1β+IFN-γ in causing amyloid-accumulation and cell-death, and both were abrogated by the HMGB1-blocker BoxA. The findings strengthen the concept of unique interactions between degenerative and inflammatory mechanisms and suggest that HMGB1/RAGE signaling is a critical pathway in IBM pathology.

[Inclusion body myositis]

The idiopathic inflammatory myopathies are systemic, chronic autoimmune diseases characterized by proximal symmetrical muscle weakness. One of the main diseases in this group is inclusion body myositis (IBM), an underdiagnosed, progressive muscle disease characteristically affecting the middle-aged and older population. It has a slow, relentlessly progressive course. The precise pathogenesis of the disease remains unknown. In most of the cases it is diagnosed a few years after the appearance of the first symptoms. The muscle biopsy typically shows endomysial inflammation, with invasion of mononuclear cells into the non-necrotic fibers, and also rimmed vacuoles. It appers, that both inflammation and degeneration are present at the onset of the disease. Our aim is to raise awareness about this disease which leads to severe disability, with clinicopathological case presentations and literature overview, emphasizing the importance of collaboration between the clinician and the neuropathologist. No effective therapy is currently available but the rapid diagnosis is essential to slow disease progression. Although this is a relatively rare disease, patients are presenting not only in immunology outpatient clinics; our reports aims to raise awareness and facilitate accurate early diagnosis of IBM.

Validity of the single limb heel raise test to predict lower extremity disablement in patients with sporadic inclusion body myositis

PURPOSE

To determine the validity of the single limb heel raise (SLHR) test as a potential screening tool to detect lower extremity disability in patients with sporadic inclusion body myositis (sIBM).

METHODS

We compared gait speed and fall history between subjects with sIBM who either could complete one SLHR (SLHR group) or could not complete one SLHR. Discriminative validity was established by comparing between group differences in functional measures based on group assignment. Receiver operating characteristics curve analysis was used to determine the predictive validity of completing one repetition on the SLHR test. Spearman correlations were used to determine the association between gait kinematics and number of repetitions achieved on the SLHR test.

RESULTS

Forty-three subjects (13 females) were studied. The SLHR group (n = 21) showed significantly greater gait speed (p < 0.001) and decreased gait aid use (p < 0.05) compared to the no SLHR group (n = 22). SLHR cut scores of 1, 20, and 22 repetitions maximized positive likelihood ratios (+LR) for the ability to walk at 54.9 (+LR. 2.2), 63.2 (+LR. 9.5), and 73.1 m/min (+LR. 5.0), respectively.

CONCLUSION

The SLHR test demonstrates adequate discriminative and predictive validity as a screening tool for lower extremity disablement in patients with sIBM. Implications for Rehabilitation The SLHR test has adequate reliability and validity to screen for the presence of lower extremity disablement in patients with sIBM. Results of this rapid field test may be used to guide the need for rehabilitation services to mitigate the effects of slow gait speeds in patients with sIBM.

[Recent progress in diagnosis and pathomechanism of inclusion body myositis]

Sporadic inclusion body myositis (sIBM) is an intractable and progressive skeletal muscle disease of unknown etiology and without effective treatment. Muscle biopsy typically reveals endomysial inflammation, invasion of mononuclear cells into non-necrotic fibers and rimmed vacuoles, suggesting inflammation and degeneration co-exist as part of the pathomechanism. We estimated the prevalence of sIBM in Japan is 1,000-1,500 in 2003 and an increase in the number of sIBM in Japan in the decade. TDP43 can be a whole mark of the muscle pathology of sIBM patients. Anti-cytosolic 5'-nucleotidase 1A (cN1A) can be a diagnostic marker of sIBM. Elucidation of the pathomechanism of sIBM is the most important to therapy. We'll also review the status of the therapeutics and clinical trials in sIBM.

[Inclusion body myositis--a rarely recognized disorder]

Inclusion body myositis is the most common disabling inflammatory myopathy in the elderly. It is more frequent in men and after the age of 50 years. Inflammatory and degenerative features coexist. There is a T-cell mediated autoimmunity driven by in situ clonally expanded cytotoxic CD8-positive T-cells invading non-necrotic muscle fibres expressing MHC-I antigen. The hallmarks of degeneration are the deposition of protein aggregates and the formation of vesicles. The course of the disease is slow and the diagnosis is usually set after several years. The muscle weakness and wasting is assymetric, affecting predominantly distal muscles of the upper extremity and proximal muscles of the legs. The signs and clinical course can be characteristic, but the diagnosis is established by muscle biopsy. There is currently no evidence based effective treatment for sIBM. Prednisone, azathioprine, methotrexate, cyclosporine and IFN-beta failed. Oxandrolon did not improve symptoms. Treatment with intravenous immunglobuline (IVIG) induced in some patients a transient improvement of swallowing and of muscle strenght, but the overall study results were negative. A T-cell depleting monoclonal antibody (alemtuzumab), in a small uncontrolled study slowed down disease progression for a six-month period. Repeated muscle biopsies showed the reduction of T-cells in the muscle and the suppression of some degeneration associated molecules. An effective therapeutic mean should act on both aspects of the pathomechanism, on the inflammatory and the degenerative processes as well.

Long-term follow-up of sporadic inclusion body myositis treated with intravenous immunoglobulin: a retrospective study of 16 patients

OBJECTIVES

Previous studies of intravenous immunoglobulin (IVIG) treatment in sporadic inclusion body myositis (sIBM) have yielded conflicting results. Here, we have undertaken a retrospective assessment of the long-term effects of IVIG in our sIBM cohort.

METHODS

Sixteen sIBM patients, treated with a mean of 10 IVIG infusions and followed up for a mean period of 23 months, were identified. Six sIBM patients treated with other drugs were used as an internal control group. Serial data on manual muscle testing (MMT), laboratory parameters and patients' subjective assessment were collected.

RESULTS

Serial MMT scores were available in 14 IVIG treated patients. Two of these patients improved more than 20% in MMT from baseline up to the third IVIG infusion. One of six patients in the control group showed a similar MMT improvement during the first six months. Improved swallowing function was reported by three IVIG-treated patients, but none of the controls. The serum levels of creatine kinase fell more than 20 % after the first IVIG infusion in 7/16 IVIG-treated patients, but this improvement was not sustained during the follow-up period.

CONCLUSIONS

IVIG treatment appears to have short-term beneficial effects on muscle strength and dysphagia in some few sIBM patients, but these effects are not sustained over time.

Prognosis and prognostic factors in sporadic inclusion body myositis

OBJECTIVES

To describe the course of change in muscle strength sporadic inclusion body myositis (IBM) patients.

MATERIAL AND METHODS

We have studied a cohort of 66 IBM pateints using a hand-held dynamometer.

RESULTS

Follow-up during a mean of 61.1 months showed a deterioration of on average -0.79% per month. The 'natural course' without immunosuppressive treatment (IS), analyzed in 43 patients (mean 46.4 months) was mean -1.03% per month. Loss of muscle power was most rapid in knee extension -1.12% (P < 0.001 when compared with elbow flexion, elbow extension and hip flexion). There was a tendency towards a more rapid decline in males than females and over the first 5 years after onset, while the level of serum creatine kinase (CK), age, or region affected at onset did not predict the prognosis. The mean change during periods with any IS treatment was -0.76% per month which was significantly lower compared to the total of untreated periods -1.03% (P < 0.05). Patients (n = 13) treated with mykofenolatmofetil showed a better prognosis of -0.67% per month (P < 0.05). In this group elbow flexion and extension and hip flexion showed a positive response, while knee extension was seemingly unaffected.

CONCLUSIONS

There is a mean of 1% loss in power per month in the untreated IBM patient - the rate of loss was greater in the quadriceps muscle and in untreated compared with IS-treated patients.

Knee extensor strength exhibits potential to predict function in sporadic inclusion-body myositis

INTRODUCTION

In this study we address the challenging issue of potential use of muscle strength to predict function in clinical trials. This has immediate relevance to translational studies that attempt to improve quadriceps strength in sporadic inclusion-body myositis (sIBM).

METHODS

Maximum voluntary isometric contraction testing as a measure of muscle strength and a battery of functional outcomes were tested in 85 ambulatory subjects with sIBM.

RESULTS

Marked quadriceps weakness was noted in all patients. Strength was correlated with distance walked at 2 and 6 minutes. Additional correlations were found with time to get up from a chair, climb stairs, and step up on curbs.

CONCLUSIONS

Quadriceps (knee extensor) strength correlated with performance in this large cohort of sIBM subjects, which demonstrated its potential to predict function in this disease. These data provide initial support for use of muscle strength as a surrogate for function, although validation in a clinical trial is required.

Inclusion body myositis in Alzheimer's disease

BACKGROUND

The prevalence of Alzheimer's disease is increasing. Could findings of similar deposits in brain and muscle tissue explain this increase? The purpose of this report is to illustrate that Alzheimer's disease and inclusion body myositis may share a common aetiology.

RESULTS

We present a case where Alzheimer's disease and inclusion body myositis coexist in the same patient. Amyloid-beta deposition and the presence of phosphorylated tau protein have been noted in brain tissue and in muscle biopsy from patients with these disorders.

METHODS

Electrophysiological methods are needed for proper diagnosis of this brain and muscle disorder. Recent data on deposit structures in both conditions may indicate an environmental aetiology for Alzheimer's disease and inclusion body myositis.

CONCLUSION

By combining electrophysiological methods with muscle biopsy in cases of Alzheimer's disease, the possible aetiological connection between simultaneous affection of both muscle and brain in this condition can be established.

[Ionic and molecular mechanisms of beta-amyloid-induced depolarization of the mouse skeletal muscle fibres]

Excess production and accumulation of beta-amyloid peptide (betaAP) are central for pathogenesis of Alzheimer's disease. Numerous studies showed that betaAP possessed wide range of toxic effects on neurons, however the mechanism of betaAP influence on another types of excitable cells, for example, skeletal muscle fibres, is unknown. In electrophysiological experiments on the mouse diaphragm, we found for the first time that betaAP (25-35 fragment, 10-6 M) disturbs the processes of the resting membrane potential generation in muscle fibres, leading to depolarization by two mechanisms: 1) inhibition of Na+,K(+)-ATPase, which leads to loss of impact of this pump to the resting membrane potential; 2) increase of membrane cationic permeability due to formation of "amyloid" channels blocked with Zn2+ ions. Our results significantly broaden current understanding of mechanisms of motor disturbances and skeletal muscle pathology in Alzheimer's disease, inclusion body myositis and other betaAP-related disorders.

Myocardial fibrosis in desmin-related hypertrophic cardiomyopathy

Desmin-related myopathy (DRM) is known to cause different types of cardiomyopathy. Late gadolinium enhancement cardiovascular magnetic resonance (CMR) has been shown to identify fibrosis in ischemic and non-ischemic cardiomyopathies. We present a rare case of desmin-related hypertrophic cardiomyopathy, CMR revealed fibrosis in the lateral wall of the left ventricle. CMR is superior to conventional echocardiography for the detection of myocardial fibrosis in desmin-related cardiomyopathy, which may be useful to detect early cardiac involvement and predict the patient prognosis.

VCP associated inclusion body myopathy and paget disease of bone knock-in mouse model exhibits tissue pathology typical of human disease

Dominant mutations in the valosin containing protein (VCP) gene cause inclusion body myopathy associated with Paget's disease of bone and frontotemporal dementia (IBMPFD). We have generated a knock-in mouse model with the common R155H mutation. Mice demonstrate progressive muscle weakness starting approximately at the age of 6 months. Histology of mutant muscle showed progressive vacuolization of myofibrils and centrally located nuclei, and immunostaining shows progressive cytoplasmic accumulation of TDP-43 and ubiquitin-positive inclusion bodies in quadriceps myofibrils and brain. Increased LC3-II staining of muscle sections representing increased number of autophagosomes suggested impaired autophagy. Increased apoptosis was demonstrated by elevated caspase-3 activity and increased TUNEL-positive nuclei. X-ray microtomography (uCT) images show radiolucency of distal femurs and proximal tibiae in knock-in mice and uCT morphometrics shows decreased trabecular pattern and increased cortical wall thickness. Bone histology and bone marrow derived macrophage cultures in these mice revealed increased osteoclastogenesis observed by TRAP staining suggestive of Paget bone disease. The VCP(R155H/+) knock-in mice replicate the muscle, bone and brain pathology of inclusion body myopathy, thus representing a useful model for preclinical studies.

Clinical features, lectin staining, and a novel GNE frameshift mutation in hereditary inclusion body myopathy

We present a comprehensive report of two siblings with hereditary inclusion body myopathy (HIBM). The clinical features and histological characteristics of the muscle biopsies showed the typical pattern of predominantly distal vacuolar myopathy with quadriceps sparing. This was confirmed by muscle MRI. PNA lectin staining showed an increased signal at the sarcolemma in patient muscle sections compared to control muscle, indicating reduced sialylation of glycoconjugates. Mutation analysis revealed compound heterozygous mutations in the GNE gene, encoding the key enzyme in sialic acid synthesis UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase: a missense mutation (c.2086G > A; p.V696M) previously described in HIBM patients of Indian origin, and a novel frame shift mutation (c.1295delA; p.K432RfsX17) leading to a premature stopcodon. These findings confirmed the diagnosis of HIBM on the histological, molecular and biochemical level.

Vacuolar myopathy in a dog resembling human sporadic inclusion body myositis

Sporadic inclusion body myositis (sIBM) is the most common myopathy in people over the age of 50 years. While immune-mediated inflammatory myopathies are well documented in dogs, sIBM has not been described. An 11-year-old dog with chronic and progressive neuromuscular dysfunction was evaluated for evidence of sIBM using current pathologic, immunohistochemical and electron microscopic diagnostic criteria. Vacuoles and congophilic intracellular inclusions were identified in cryostat sections of multiple muscle biopsies and immunostained with antibodies against amyloid-β peptide, amyloid-β precursor protein, and proteosome 20S of the ubiquitin–proteosome system. Cellular infiltration and increased expression of MHC Class I antigen were observed. Cytoplasmic filamentous inclusions, membranous structures, and myeloid bodies were identified ultrastructurally. These observations constitute the first evidence that both the inflammatory and degenerative features of human sIBM can occur in a non-human species.

Fast-twitch sarcomeric and glycolytic enzyme protein loss in inclusion body myositis

Inclusion body myositis (IBM) is an inflammatory disease of skeletal muscle of unknown cause. To further understand the nature of the tissue injury in this disease, we developed methods for large-scale detection and quantitation of proteins in muscle biopsy samples and analyzed proteomic data produced by these methods together with histochemical, immunohistochemical, and microarray data. Twenty muscle biopsy samples from patients with inflammatory myopathies (n = 17) or elderly subjects without neuromuscular disease (n = 3) were profiled by proteomic studies using liquid chromatographic separation of peptides followed by mass spectrometry. Thirteen of the diseased samples additionally underwent microarray studies. Seventy muscle specimens from patients with a range of neuromuscular disorders were examined by ATPase histochemical methods. Smaller numbers of samples underwent immunohistochemical and immunoblot studies. Mass spectrometric studies identified and quantified approximately 300 total distinct proteins in each muscle sample. In IBM and to a lesser extent in polymyositis, proteomic studies confirmed by histochemical, immunohistochemical, and immunoblot studies showed loss of many fast-twitch specific structural proteins and glycolytic enzymes despite relative preservation of transcript levels. Increased abundance of a nuclear membrane protein, immunoglobulins, and two calpain-3 substrates were present. The atrophy present in IBM muscle is accompanied by preferential loss of fast-twitch structural proteins and glycolytic enzymes, particularly glycogen debranching enzyme, with relative preservation of the abundance of their respective transcripts. Although muscle atrophy has long been recognized in IBM, these studies are the first to report specific proteins which are reduced in quantity in IBM muscle.

Effect of Alemtuzumab (CAMPATH 1-H) in patients with inclusion-body myositis

Sporadic inclusion-body myositis (sIBM) is the most common disabling, adult-onset, inflammatory myopathy histologically characterized by intense inflammation and vacuolar degeneration. In spite of T cell-mediated cytotoxicity and persistent, clonally expanded and antigen-driven endomysial T cells, the disease is resistant to immunotherapies. Alemtuzumab is a humanized monoclonal antibody that causes an immediate depletion or severe reduction of peripheral blood lymphocytes, lasting at least 6 months. We designed a proof-of-principle study to examine if one series of Alemtuzumab infusions in sIBM patients depletes not only peripheral blood lymphocytes but also endomysial T cells and alters the natural course of the disease. Thirteen sIBM patients with established 12-month natural history data received 0.3 mg/kg/day Alemtuzumab for 4 days. The study was powered to capture > or =10% increase strength 6 months after treatment. The primary end-point was disease stabilization compared to natural history, assessed by bi-monthly Quantitative Muscle Strength Testing and Medical Research Council strength measurements. Lymphocytes and T cell subsets were monitored concurrently in the blood and the repeated muscle biopsies. Alterations in the mRNA expression of inflammatory, stressor and degeneration-associated molecules were examined in the repeated biopsies. During a 12-month observation period, the patients' total strength had declined by a mean of 14.9% based on Quantitative Muscle Strength Testing. Six months after therapy, the overall decline was only 1.9% (P < 0.002), corresponding to a 13% differential gain. Among those patients, four improved by a mean of 10% and six reported improved performance of daily activities. The benefit was more evident by the Medical Research Council scales, which demonstrated a decline in the total scores by 13.8% during the observation period but an improvement by 11.4% (P < 0.001) after 6 months, reaching the level of strength recorded 12 months earlier. Depletion of peripheral blood lymphocytes, including the naive and memory CD8+ cells, was noted 2 weeks after treatment and persisted up to 6 months. The effector CD45RA(+)CD62L(-) cells, however, started to increase 2 months after therapy and peaked by the 4th month. Repeated muscle biopsies showed reduction of CD3 lymphocytes by a mean of 50% (P < 0.008), most prominent in the improved patients, and reduced mRNA expression of stressor molecules Fas, Mip-1a and alphaB-crystallin; the mRNA of desmin, a regeneration-associated molecule, increased. This proof-of-principle study provides insights into the pathogenesis of inclusion-body myositis and concludes that in sIBM one series of Alemtuzumab infusions can slow down disease progression up to 6 months, improve the strength of some patients, and reduce endomysial inflammation and stressor molecules. These encouraging results, the first in sIBM, warrant a future study with repeated infusions

Idiopathic inflammatory myopathies

Since the description of the first case of dermatomyositis over a century ago, our understanding of myositis has evolved. Bohan and Peter in 1975 established diagnostic criteria for polymyositis and dermatomyositis. Subsequent investigations by Arahata and Engel delineated differences in the lymphocyte subsets on muscle histopathology distinguishing polymyositis and dermatomyositis. Following that, myositis-specific antibodies have been reported in association with various myositis subtypes and with interstitial lung disease. Polymyositis and dermatomyositis are in general responsive to immunosuppressive therapy. Inclusion body myositis (IBM) became recognized as a distinct entity nearly half a century ago. IBM is clinically and pathologically distinct from the other inflammatory myopathies. The weakness in IBM is characteristic, involving both the proximal and distal muscle groups, such as finger flexion, knee extension and ankle dorsiflexion. Vacuolated fibers, amyloid deposition, and filaments on electron microscopy are pathologic hallmarks of IBM. IBM is refractory to corticosteroids and intravenous gamma globulins. This clinical observation and the pathologic features support the hypothesis that IBM is a muscle-degenerative disease. Most recently, a fourth inflammatory myopathy subtype called necrotizing myopathy was described. Necrotizing myopathy may be related to malignancy, other autoimmune diseases, toxic exposure or can be idiopathic. The key histopathologic findings of this entity are necrotic fibers undergoing phagocytosis. Though patients ultimately respond to immunosuppressive therapy, they tend to be more refractory and therefore often require a more aggressive treatment approach.

Discriminating neurogenic from myopathic disease via measurement of muscle anisotropy

Skeletal muscle is electrically anisotropic, with a tendency for applied electrical current to flow more readily along muscle fibers than across them. In this study, we assessed a method for non-invasive measurement of anisotropy to determine its potential to serve as a new technique for distinguishing neurogenic from myopathic disease. Measurements were made on the biceps brachii and tibialis anterior muscles in 15 normal subjects and 12 patients with neuromuscular disease (6 with amyotrophic lateral sclerosis and 6 with various myopathies) using 50 kHZ applied current. Consistent multi-angle anisotropic patterns were found for reactance and phase in both muscles in normal subjects. Normalized anisotropy differences for each subject were defined, and group average values identified. The amyotrophic lateral sclerosis (ALS) patients demonstrated increased and distorted anisotropy patterns, whereas myopathic patients demonstrated normal or reduced anisotropy. These results suggest that non-invasive measurement of muscle anisotropy has potential for diagnosis of neuromuscular diseases.

Amyloid-β protein impairs Ca2+ release and contractility in skeletal muscle

Inclusion body myositis (IBM), the most common muscle disorder in the elderly, is partly characterized by dysregulation of β-amyloid precursor protein (βAPP) expression and abnormal, intracellular accumulation of full-length βAPP and β-amyloid epitopes. The present study examined the effects of β-amyloid accumulation on force generation and Ca(2+) release in skeletal muscle from transgenic mice harboring human βAPP and assessed the consequence of Aβ(1-42) modulation of the ryanodine receptor Ca(2+) release channels (RyRs). β-Amyloid laden muscle produced less peak force and exhibited Ca(2+) transients with smaller amplitude. To determine whether modification of RyRs by β-amyloid underlie the effects observed in muscle, in vitro Ca(2+) release assays and RyR reconstituted in planar lipid bilayer experiments were conducted in the presence of Aβ(1-42). Application of Aβ(1-42) to RyRs in bilayers resulted in an increased channel open probability and changes in gating kinetics, while addition of Aβ(1-42) to the rabbit SR vesicles resulted in RyR-mediated Ca(2+) release. These data may relate altered βAPP metabolism in IBM to reductions in RyR-mediated Ca(2+) release and muscle contractility.

Inclusion-body myositis: muscle-fiber molecular pathology and possible pathogenic significance of its similarity to Alzheimer's and Parkinson's disease brains

Sporadic inclusion-body myositis (s-IBM), the most common muscle disease of older persons, is of unknown cause and lacks successful treatment. Here we summarize diagnostic criteria and discuss our current understanding of the steps in the pathogenic cascade. While it is agreed that both degeneration and mononuclear-cell inflammation are components of the s-IBM pathology, how each relates to the pathogenesis remains unsettled. We suggest that the intra-muscle-fiber degenerative component plays the primary role, leading to muscle-fiber destruction and clinical weakness, since anti-inflammatory treatments are not of sustained benefit. We discuss possible treatment strategies aimed toward ameliorating a degenerative component, for example, lithium and resveratrol. Also discussed are the intriguing phenotypic similarities between s-IBM muscle fibers and the brains of Alzheimer and Parkinson's diseases, the most common neurodegenerative diseases associated with aging. Similarities include, in the respective tissues, cellular aging, mitochondrial abnormalities, oxidative and endoplasmic-reticulum stresses, proteasome inhibition and multiprotein aggregates.

Histone H1 is released from myonuclei and present in rimmed vacuoles with DNA in inclusion body myositis

To investigate myonuclear alterations in sporadic inclusion body myositis (s-IBM), we immuno-localized histones in muscles in 11 patients. The examination showed that vacuolar rims were frequently positive for histone H1. In triple-color fluorescence study, the H1-positive products were found on the inner side of an emerin-positive circle with DNA. Moreover, H1-positive materials appeared to be released into the cytoplasm in some vacuoles and myonuclei. The localization of H1 was different from phosphorylated Elk-1, which is a nuclear protein, but abnormally accumulated in the cytoplasm in s-IBM. The results strongly support the hypothesis that rimmed vacuoles are derived from the nucleus. The cytoplasmic H1-release suggests dysfunction of nuclear membranes in an early phase of the nuclear disintegration. We hypothesize that, in s-IBM muscles, compromised nuclear envelope may permit release of some nuclear components such as histone H1 and cannot facilitate the incorporation of others to the nucleus as in pElk-1.

An Italian family with inclusion-body myopathy and frontotemporal dementia due to mutation in theVCP gene

Mutations of the valosin-containing protein gene (VCP) are responsible for autosomal-dominant hereditary inclusion-body myopathy associated with frontotemporal dementia and Paget's disease of bone. We identified the p.R155C missense mutation in the VCP gene segregating in an Italian family with three affected siblings, two of whom had a progressive myopathy associated with dementia, whereas one exhibited a progressive myopathy and preclinical signs of Paget's disease of bone. Our study demonstrates that VCP mutations are found in patients of Italian background and may lead to a variable clinical phenotype even within the same kinship.

Brain imaging and neuropsychology in late-onset dementia due to a novel mutation (R93C) of valosin-containing protein

Inclusion body myopathy with Paget disease of bone and frontotemporal dementia (IBMPFD, MIM 167320) is a recently identified autosomal dominant disorder due to mutations in the valosin-containing protein (VCP) that affects muscle, bone and brain. Brain involvement and neuropsychological findings of IBMPFD have not been described in detail. A patient carried a novel heterozygous base pair change, 47832C>T, in the VCP gene that resulted in substitution of an arginine residue by cysteine at position 93 (R93C). He presented first with myopathy while bone involvement remained subclinical. The patient developed behavioral abnormalities in his 60s and showed frank personality change with fluent empty speech at the age of 74 years. This syndrome was best classified as semantic dementia. Magnetic resonance imaging disclosed slight but progressive cerebral atrophy with prominent callosal and frontal white matter loss. Positron emission tomography demonstrated glucose hypometabolism of the frontal and temporal lobes disproportionate to their structural involvement. This first comprehensive clinical and neuroimaging study in IBMPFD may raise the awareness among clinicians as well as basic scientists for this exemplary genetic model of dementia.

NOGO is increased and binds to BACE1 in sporadic inclusion-body myositis and in A beta PP-overexpressing cultured human muscle fibers

Increased amyloid-beta precursor protein (A beta PP) and amyloid-beta (A beta) accumulation appear to be upstream steps in the pathogenesis of sporadic inclusion-body myositis (s-IBM). BACE1, participating in A beta production is also increased in s-IBM muscle fibers. Nogo-B and Nogo-A belong to a family of integral membrane reticulons, and Nogo-B binding to BACE1 blocks BACE1 access to A beta PP, decreasing A beta production. We studied Nogo-B and Nogo-A in s-IBM muscle and in our IBM muscle culture models, based on A beta PP-overexpression or ER-stress-induction in cultured human muscle fibers (CHMFs). We report that: (1) in biopsied s-IBM fibers, Nogo-B is increased, accumulates in aggregates, is immuno-co-localized with BACE1, and binds to BACE1; Nogo-A is undetectable. (2) In CHMFs, (a) A beta PP overexpression increases Nogo-B, Nogo-A, and BACE1, (b) ER stress increases BACE1 but decreases Nogo-B and Nogo-A, (c) Nogo-B and Nogo-A associate with BACE1. Accordingly, two novel mechanisms, A beta PP overexpression and ER stress, are involved in Nogo-B and Nogo-A expression in human muscle. We propose that in s-IBM muscle the Nogo-B increase may represent an attempt by muscle fiber to decrease A beta production. However, the increase of Nogo-B seems insufficient because A beta continues to accumulate and the disease progresses. We propose that manipulations, which increase Nogo-B in s-IBM muscle might offer a new therapeutic opportunity.

Correlation of muscle biopsy, clinical course, and outcome in PM and sporadic IBM

OBJECTIVE

To correlate muscle biopsy findings with prebiopsy and postbiopsy clinical course and response to therapy in polymyositis (PM) and sporadic inclusion body myositis (IBM).

BACKGROUND

Existence of pure PM has recently been questioned; subsequently, the definition and criteria for diagnosing PM were debated.

METHODS

Patient records, follow-up information, and muscle biopsies were analyzed in 107 patients whose biopsies were initially read as PM and IBM.

RESULTS

The patients fell into three groups by combined biopsy and clinical criteria: PM, 27 patients; IBM, 64 patients; PM/IBM, 16 patients with biopsy diagnosis of PM but clinical features of IBM. For the three groups, the respective mean periods from disease onset to end of follow-up were 5.9, 8.5, and 9.6 years. Another autoimmune disease was present in 4 of 27 PM, 8 of 64 IBM, and 1 of 16 PM/IBM cases. An autoimmune serologic marker occurred in one-third of each group. Nineteen PM patients had no associated autoimmune disease or marker. Nonnecrotic fiber invasion by mononuclear cells appeared in all IBM, 17 of 27 PM, and 13 of 16 PM/IBM patients. The density of both invaded fibers and cytochrome-c oxidase-negative fibers was higher in IBM and PM/IBM than in PM. Immunotherapy improved 22 of 27 PM patients but had only transient beneficial effects in 2 of 32 IBM and 1 of 14 PM/IBM patients.

CONCLUSIONS

1) Sixteen of 43 patients (37%) with biopsy features of polymyositis (PM) had clinical features of inclusion body myositis (IBM). 2) Absence of canonical biopsy features of IBM from clinically affected muscles of IBM patients challenges biopsy criteria for IBM, or the IBM markers appear late in some patients, or their distribution in muscle is patchy and restricted compared with that of the inflammatory exudate. 3) The muscle biopsy is a reliable instrument in the diagnosis of PM and IBM in close to 85% of the patients. Errors of diagnosis in the remaining 15% can be avoided or reduced by combined evaluation of the clinical and pathologic findings.

Upregulation of thrombospondin-1(TSP-1) and its binding partners, CD36 and CD47, in sporadic inclusion body myositis

The TSP1/CD36/CD47-complex is involved in T cell expansion and inflammatory responses to beta-amyloid, both relevant to IBM. We report on the mRNA and protein expression of TSP1/ CD36 /CD47-complex in IBM muscles and in human myoblasts after cytokine stimulation. The TSP1/CD36 /CD47 was upregulated in IBM. TSP1 immunolocalized to the connective tissue contiguous to inflammation and CD36/CD47 on the myofibers and CD8+ cells. Further, TNF-alpha upregulated the production of TSP1 and CD47 by myoblasts. The TSP-complex is another inflammatory mediator associated with chronic inflammation in IBM that may perpetuate the immune responses to local antigens in response to TNF-alpha.

Single-fiber electromyography in sporadic inclusion body myopathy

OBJECTIVE

To report the SFEMG findings in sporadic inclusion body myopathy (S-IBM).

METHODS

We have analyzed the SFEMG data in 25 patients (mean age: 63; 16 males) with S-IBM which was diagnosed by the presence of classical rimmed vacuoles in the muscle biopsy together with clinical, laboratory, and electrophysiological findings.

RESULTS

All patients had fibrillations, positive sharp waves, and small-amplitude short-duration motor unit potentials (MUPs) in the needle EMG. High-amplitude MUPs were observed in eight (32%) patients, two of whom had long-duration MUPs. SFEMG was abnormal in 17 (68%) cases: mean "mean consecutive difference (MCD)" was increased beyond the age-adjusted normal limit in 16 cases, and more than 10% of potential pairs (PP) had MCD longer than the upper normal limit of an individual MCD in one case. Mean fiber density (FD) was 2.16, with maximum FD being 4.15. Increased FD was noted in 11 (44%) cases. In four cases, more than 10% of PP had blocking, but there was no neurogenic blocking in any PP. As expected, MCD increased linearly (r=0.85) with the percentage of PP beyond the normal upper limit.

CONCLUSIONS

The SFEMG findings in S-IBM are typical of the classical pattern of myopathy.

SIGNIFICANCE

Our findings support the consensus that S-IBM is a myopathy.

Serial quantitative electrophysiologic studies in sporadic inclusion body myositis

Sporadic inclusion body myositis (S-IBM) is a progressive, acquired myopathic process of unknown etiology. No known, successful or proven treatment exists. Quantitative EMG studies including concentric needle motor unit action potentials, interference pattern, macro-EMG and fiber density have allowed different measures to be made of the motor unit. These different measures allow inferences to be made in how the muscle fibers are distributed within both the normal and diseased motor unit. The present study is an effort to use multiple quantitative EMG measurements from the biceps brachii on a serial basis in order to study chronic changes in the motor unit with disease progression. Twenty-eight studies from 9 patients over a four-year period are shown. We conclude that while the concentric needle electrode is most helpful for diagnosing abnormality, the less selective macro-EMG and surface electrodes are better suited to monitor disease progression, especially in very weak muscles. These observations have practical applications for monitoring disease progression, or conversely, response to treatment.

Pathogenic point mutations in a transmembrane domain of the epsilon subunit increase the Ca2+ permeability of the human endplate ACh receptor

The epsilon subunit of the human endplate ACh receptor (AChR) is a key determinant of the large fraction of the ACh-evoked current carried by Ca2+ ions (P(f)). Consequently, missense mutations in the epsilon subunit are potential targets for altering the P(f) of human AChR. In this paper we investigate the effects of two pathogenic point mutations in the M2 transmembrane segment AChR epsilon subunit, epsilonT264P and epsilonV259F, that cause slow-channel syndromes (SCS). When expressed in GH4C1 cells, the mutant receptors subunits raise Ca2+ permeability of the receptors approximately 1.5 and approximately 2-fold above that of wild-type, to attain P(f) values of 11.8% (epsilonT264P) and 15.4% (epsilonV259F). The latter value exceeds most P(f) values reported to date for ligand-gated ion channels. Consistent with these findings, the biionic Ca2+ permeability ratio (P(Ca)/P(Cs)) of the mutant AChRs is also increased. Upon repetitive stimulation with ACh, the mutant receptors show an enhanced current run-down compared with wild-type, leading to a strong reduction of their function. We propose that the enhanced Ca2+ permeability of the mutant receptors overrides the protective effect of desensitization and, together with the prolonged opening events of the AChR channel, is an important determinant of the excitotoxic endplate damage in the SCS.

Myopathy associated with gluten sensitivity

Ataxia and peripheral neuropathy are the most common neurological manifestations of gluten sensitivity. Myopathy is a less common and poorly characterized additional neurological manifestation of gluten sensitivity. We present our experience with 13 patients who presented with symptoms and signs suggestive of a myopathy and in whom investigation led to the diagnosis of gluten sensitivity. Three of these patients had a neuropathy with or without ataxia in addition to the myopathy. The mean age at onset of the myopathic symptoms was 54 years. Ten patients had neurophysiological evidence of myopathy. Inflammatory myopathy was the most common finding on neuropathological examination. One patient had basophilic rimmed vacuoles suggestive of inclusion-body myositis. Six patients received immunosuppressive treatment in addition to starting on a gluten-free diet; five improved and one remained unchanged. Among seven patients not on immunosuppressive treatment, four showed clinical improvement of the myopathy with a gluten-free diet. The improvement was also associated with reduction or normalization of serum creatine kinase level. The myopathy progressed in one patient who refused the gluten-free diet. Myopathy may be another manifestation of gluten sensitivity and is likely to have an immune-mediated pathogenesis. A gluten-free diet may be a useful therapeutic intervention.

AbetaPP-overexpression and proteasome inhibition increase alphaB-crystallin in cultured human muscle: relevance to inclusion-body myositis

Amyloid-beta precursor protein (AbetaPP) and its fragment amyloid-beta (Abeta) are increased in s-IBM muscle fibers and appear to play an important role in the pathogenic cascade. alphaB-Crystallin (alphaBC) was shown immunohistochemically to be accumulated in s-IBM muscle fibers, but the stressor(s) influencing alphaBC accumulation was not identified. We now demonstrate, using our experimental IBM model based on genetic overexpression of AbetaPP into cultured normal human muscle fibers, that: (1) AbetaPP overexpression increased alphaBC 3.7-fold (p=0.025); (2) additional inhibition of proteasome with epoxomicin increased alphaBC 7-fold (p=0.002); and (3) alphaBC physically associated with AbetaPP and Abeta oligomers. We also show that in biopsied s-IBM muscle fibers, alphaBC was similarly increased 3-fold (p=0.025) and physically associated with AbetaPP and Abeta oligomers. We propose that increased AbetaPP is a stressor increasing alphaBC expression in s-IBM muscle fibers. Determining the consequences of alphaBC association with Abeta oligomers could have clinical therapeutic relevance.

Proteomic analysis of inclusion body myositis

Sporadic inclusion body myositis (IBM) is the most frequently acquired inflammatory myopathy of late adult life, yet its diagnostic criteria and pathogenesis remain poorly defined. Because effective treatment is lacking, research efforts have intensified to identify specific markers for this debilitating disorder. In this study, proteomic analysis of 4 cases of sporadic IBM was compared with 5 cases of inflammatory myopathy without clinicopathologic features of IBM to distinguish the IBM-specific proteome. Proteins were separated by 2-dimensional polyacrylamide gel electrophoresis and profiled by mass spectrometric sequencing. Expression of most proteins remained unchanged; however, 16 proteins were upregulated and 6 proteins were downregulated in IBM compared with cases of non-IBM inflammatory myopathy. These IBM-specific proteins included apolipoprotein A-I, amyloid beta precursor protein, and transthyretin, which have been associated with amyloidosis; superoxide dismutase, enolase, and various molecular chaperones indicate perturbations in detoxification, energy metabolism, and protein folding, respectively. The IBM-downregulated proteins mainly serve as carriers for muscle contraction and other normal muscle functions. We further applied Western blot and immunohistochemistry to verify the proteomic findings. This study validates proteomics as a powerful tool in the study of muscle disease and indicates a unique pattern of protein expression in IBM.

Serum Levels of Matrix Metalloproteinases-2 and -9 and Their Tissue Inhibitors in Inflammatory Neuromuscular Disorders

We monitored serum levels of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) before and during intravenously applied immunoglobulin (IVIG) therapy in 33 patients with chronic immune-mediated neuropathies and myopathies and 15 controls. Baseline MMP-2 and TIMP-2 serum levels were lower and MMP-9 and TIMP-1 serum levels higher in all patients compared to age-matched controls. Eight days after IVIG treatment, MMP-2, TIMP-2, and TIMP-1 serum levels increased, while MMP-9 serum levels decreased, indicating tissue repair. After 60 days, MMP-9 levels increased, MMP-2 approached normal levels, while TIMP-1 and TIMP-2 serum levels were below day 8 levels, indicating relapsing tissue damage. Comparing the MMP/TIMP results with the clinical courses, IVIG treatment tended to change MMP/TIMP levels in a way that paralleled clinical improvement and relapse. In sum, during a distinct time period, IVIG therapy seems to be able to modulate MMP-mediated tissue repair.

Platelet-endothelial cell adhesion molecule-1 and CD146: soluble levels and in situ expression of cellular adhesion molecules implicated in the cohesion of endothelial cells in idiopathic inflammatory myopathies

OBJECTIVE

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of diseases characterized by chronic inflammation of muscles. We investigated the role of cellular adhesion molecules implicated in the cohesion of endothelial cells in IIM.

METHODS

In 22 patients with IIM we investigated plasma concentrations of soluble junctional adhesion molecules [platelet-endothelial cell adhesion molecule (sPECAM-1) and sCD146] and cellular adhesion molecules [sP-selectin, sE-selectin, intercellular adhesion molecule (sICAM-1), and vascular cell adhesion molecule (sVCAM-1)] implicated in leukocyte/endothelial cell interactions. Results were compared to a control group. Muscle biopsy samples from 8 out of 22 IIM patients were studied by immunohistochemistry for tissue expression of these molecules and compared to normal muscle samples. PECAM-1 and CD146 expression was also studied using immunoblots from muscle biopsies from 5 patients and 2 controls.

RESULTS

We observed distinct patterns of soluble levels and in situ expression between dermatomyositis (DM), polymyositis (PM), and sporadic inclusion body myositis (s-IBM). PM samples showed significantly increased levels of sCD146, sPECAM-1, and s-ICAM1 and increased expression of CD146, CD31, and ICAM-1 in endothelial cells, whereas CD146 and ICAM-1 were also recorded in some muscle fibers. In DM, sE-selectin, sP-selectin, and sPECAM-1 were significantly increased, with abnormal expression of ICAM-1 in endothelial cells and perifascicular muscle fibers. In the small group of s-IBM samples, results were similar to PM, but the only significant increase was the level of sPECAM-1. Immunoblots confirmed increased expression of PECAM-1 and CD146 in all IIM muscles in comparison to controls, with the highest expression in PM and IBM samples.

CONCLUSION

We observed abnormal increases of soluble levels of adhesion molecules implicated in endothelial cell junctions in PM (sCD146, sPECAM-1) and to a lesser extent in DM and s-IBM (sPECAM-1). We conclude that the distinctly different profiles between PM/s-IBM and DM reflect differences in the pathophysiological background of these diseases.

Raised troponin T in inclusion body myositis is common and serum levels are persistent over time

Cardiac Troponin T (cTnT), creatine kinase (CK) and creatine kinase isoenzyme MB (CKMB) were measured in 42 consecutive patients with sporadic inclusion body myositis (s-IBM). 26 patients (62%) had a cTnT level >0.05 microg/L, the cut off used in the diagnosis of myocardial infarction. The cTnT levels correlated somewhat more closely to CKMB (rho=0.83, p<0.0001) than to CK (rho=0.60, p<0.0001). Patients on immunosuppressive treatment had lower cTnT levels than untreated, while there were no significant differences according to age, disease duration or gender. Repeated samples in 26 patients showed that the cTnT levels were essentially unchanged over time up to 17 months. None of the patients had signs of myocardial damage or renal failure at time of sampling. It may be of value to analyse cTnT at some occasion(s) in s-IBM patients.

Needle electromyographic findings in 98 patients with myositis

BACKGROUND/AIMS

Little is known about the distribution of electromyographic (EMG) abnormalities in myositis even though this is relevant in daily practice.

METHODS

A retrospective semiquantitative analysis of needle EMG findings was performed in a group of 98 patients with myositis. The frequency, type, and distribution of abnormalities were studied. The influence of the use of corticosteroids and the stage of the disease were evaluated.

RESULTS

In most patients, a myopathic pattern with spontaneous activity was found, although several clinically relevant exceptions were noted. Long-duration motor unit potentials were found in all three diagnostic groups and were not associated with disease duration. In the lower extremity a distal to proximal gradient was present, adding to the diagnostic confusion with neurogenic diseases, and spontaneous activity was absent in a relatively large group although none of the patients in the acute stage of the disease had a normal EMG. The use of corticosteroids reduced the number of abnormal findings in dermatomyositis and polymyositis, but not in inclusion body myositis.

CONCLUSION

A myopathic pattern with spontaneous activity was most frequently found, although several clinically relevant exceptions were noted. These results illustrate the spectrum of EMG findings in myositis, and may aid the clinician in the interpretation of the EMG in these patients.

Plasma cells in muscle in inclusion body myositis and polymyositis

BACKGROUND

Previous immunohistochemical studies of muscle from patients with inclusion body myositis and polymyositis found many more T cells than B cells, suggesting a role for intramuscular cell-mediated immune mechanisms rather than humoral mechanisms.

METHODS

Microarray studies were performed on muscle biopsy specimens from 40 patients with inclusion body myositis (IBM; n = 23), polymyositis (PM; n = 6), and without neuromuscular disease (n = 11). Reverse transcription PCR of selected immunoglobulin gene transcripts was performed on two patient samples. Qualitative immunohistochemical studies for B-cell lineage cell surface markers were performed on 28 muscle specimens and quantitative studies performed on a subset of 19 untreated patients with IBM or PM. CD138+ cells were isolated from muscle using laser capture microdissection, and immunoglobulin transcripts were PCR amplified to determine the presence or absence of immunoglobulin gene rearrangements unique to the B-cell lineage.

RESULTS

Immunoglobulin gene transcripts accounted for 59% in IBM and 33% in PM of the most stringently defined highest differentially expressed muscle transcripts compared with normal. Plasma cells, terminally differentiated B cells expressing CD138 but not CD19 or CD20, are present in IBM and PM muscle in numbers several times higher than B cells.

CONCLUSIONS

There are differentiated B cells in the form of CD138+ plasma cells within the muscle of patients with inclusion body myositis and polymyositis. The principle of linked recognition of B-cell activation predicts several strategies for autoantigen discovery that could not otherwise be pursued through the study of the infiltrating T-cell population alone.

Diagnosis, pathogenesis and treatment of inclusion body myositis

PURPOSE OF REVIEW

We provide an update of progress gained from research into sporadic inclusion body myositis (s-IBM).

RECENT FINDINGS

Most research on s-IBM has focused on the inflammatory reaction or the accumulation of pathological proteins in vacuolated muscle fibres. The inflammatory reaction is characterized by clonal expansions of lymphocytes, predominantly CD8 cytotoxic T cells, which invade and destroy muscle fibres. That costimulatory molecules have been identified demonstrates that muscle fibres can act as antigen presenting cells, and the expression of various chemokines in muscle indicates their importance in the immunopathogenesis of s-IBM. The region of interest for a susceptibility gene in the major histocompatibility complex has been narrowed, and for the first time it has been demonstrated that a chronic viral infection can trigger the inflammatory process leading to s-IBM. The nature of the accumulated material associated with the vacuoles has been extensively investigated over the past few years. Amyloid-beta and phosphorylated tau protein in intracellular inclusions are a characteristic finding in s-IBM, which may lead to calcium dyshomeostasis and endoplasmic reticulum stress. The proteasomal system is upregulated, including immunoproteasomes. 'Molecular misreading' leading to ubiquitin mRNA mutations and accumulation of pathological ubiquitin in muscle fibres may be associated with proteasomal dysfunction. There is still no efficient treatment for s-IBM, but the effects of new, more specific immunotherapies have begun to be explored.

SUMMARY

Recent findings indicate that both inflammatory reaction and abnormal protein accumulation are important for the pathogenesis in s-IBM. The link between them continues to await elucidation.

Neprilysin participates in skeletal muscle regeneration and is accumulated in abnormal muscle fibres of inclusion body myositis

Neprilysin (NEP, EP24.11), a metallopeptidase originally shown to modulate signalling events by degrading small regulatory peptides, is also an amyloid-beta- (Abeta) degrading enzyme. We investigated a possible role of NEP in inclusion body myositis (IBM) and other acquired and hereditary muscle disorders and found that in all myopathies NEP expression was directly associated with the degree of muscle fibre regeneration. In IBM muscle, NEP protein was also strongly accumulated in Abeta-bearing abnormal fibres. In vitro, during the experimental differentiation of myoblasts, NEP protein expression was regulated at the post-transcriptional level with a rapid increase in the early stage of myoblast differentiation followed by a gradual reduction thereafter, coincident with the progression of the myogenic programme. Treatment of differentiating muscle cells with the NEP inhibitor dl-3-mercapto-2-benzylpropanoylglycine resulted in impaired differentiation that was mainly associated with an abnormal regulation of Akt activation. Therefore, NEP may play an important role during muscle cell differentiation, possibly through the regulation, either directly or indirectly, of the insulin-like growth factor I-driven myogenic programme. In IBM muscle increased NEP may be instrumental in (i) reducing the Abeta accumulation in vulnerable fibres and (ii) promoting a repair/regenerative attempt of muscle fibres possibly through the modulation of insulin-like growth factor I-dependent pathways.

Clinical and muscle magnetic resonance imaging study of an Italian family with autosomal dominant inclusion body myopathy not linked to known genetic loci

The objective was to report a clinical, pathological and muscle magnetic resonance (MR) study of an Italian family with an autosomal dominant inclusion body myopathy (AD-IBM). Eight subjects (age range 20-56 years; 5 females and 3 males) belonging to four generations were studied. Onset of disturbances (distal weakness at lower limbs) ranged from 20 to 28 years. CK levels were increased to five times. Only in an early stage oedema of involved muscles has been demonstrated by muscle MR. Quadriceps femoris was characteristically spared; in the last phases a mild involvement of the vasti became evident with persistent sparing of the rectus femori. Rimmed vacuoles and hyperphosphorylated tau filaments were evident at muscle biopsy. Linkage analysis excluded the association of the disease to chromosome loci 14q11, 17p13.1, 2p13, 19p13. The study suggests that quadriceps sparing is a characteristic feature also of AD-IBM. This finding could represent a muscle-image hallmark helpful in diagnosis of autosomal dominant muscular disorders.

Inclusion body myopathy and Paget disease is linked to a novel mutation in the VCP gene

Mutations in the valosin-containing protein (VCP) on chromosome 9p13-p12 were recently found to be associated with hereditary inclusion body myopathy, Paget disease of the bone, and frontotemporal dementia (IBMPFD). We identified a novel missense mutation in the VCP gene (R159H; 688G>A) segregating with this disease in an Austrian family of four affected siblings, who exhibited progressive proximal myopathy and Paget disease of the bone but without clinical signs of dementia.

Inflammatory disorders of muscle: progress in polymyositis, dermatomyositis and inclusion body myositis

PURPOSE OF REVIEW

To provide an update on the major advances in inflammatory myopathies.

RECENT FINDINGS

Polymyositis is an uncommon disorder that can be misdiagnosed when the old, and never validated, criteria of Bohan and Peter are used. New diagnostic criteria were recently introduced, in which the MHC/CD8 complex is considered a specific immunopathological marker because it distinguishes the antigen-driven inflammatory cells that characterize polymyositis and sporadic inclusion-body myositis from the non-specific, secondary inflammation seen in other disorders, such as dystrophies. In sporadic inclusion-body myositis the inflammatory cells invade non-vacuolated fibers, whereas the vacuolated fibers are not invaded by T cells, implying two independent processes, a primary immune process with antigen-driven T cells identical to polymyositis, and a degenerative process in which beta-amyloid and amyloid-related proteins participate in vacuolar degeneration. In polymyositis and sporadic inclusion-body myositis, antigen-specific and clonally expanded autoinvasive T cells persist for years, even in different muscles, as reconfirmed by proof-of-principle techniques involving CDR3 spectratyping combined with laser microdissected single-cell polymerase chain reaction of the T-cell receptor genes. The formation of immunological synapse between autoinvasive T cells and muscle fibers was recently strengthened by the upregulation of co-stimulatory molecules ICOS/ICOS-L and PD-L1. A new, distinct myopathy characterized by T-cell-triggered macrophage hyperactivation has now been recognized in patients with dermatomyositis-like disease.

SUMMARY

Despite recent progress, the antigen(s) responsible for T-cell activation in polymyositis and sporadic inclusion-body myositis and the cause of vacuolar degeneration in sporadic inclusion-body myositis remain unclear. Newer, more aggressive immunotherapies may be encouraging, but control trials are needed to prove efficacy.

Preservation of in vitro muscle fiber function in dermatomyositis and inclusion body myositis: a single fiber study

Five patients with untreated dermatomyositis, five with inclusion body myositis, and 16 healthy elderly volunteer subjects (controls) underwent open (dermatomyositis and inclusion body myositis) or percutaneous (controls) muscle biopsy. Biopsied muscles included deltoid, biceps and vastus lateralis. Chemically skinned single muscle fibers were activated with Ca(+2); the slack test was performed to determine maximal unloaded shortening velocity (Vo). Parameters measured include single fiber cross sectional area, maximal force, specific force and Vo. 429 Type I and 94 Type IIA fibers were studied. Cross sectional area and maximal force were greater in inclusion body myositis than dermatomyositis or control for Type I and IIA fibers. Specific force of Type I fibers was similar in inclusion body myositis and dermatomyositis but greater than in controls. Vo was greater in Type I, but not IIA, fibers in dermatomyositis compared with inclusion body myositis and controls. The force and velocity generating capacity of single muscle fibers is preserved in patients with dermatomyositis and inclusion body myositis suggesting that dysfunction of the contractile proteins does not contribute to clinical muscle weakness.

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.