Inclusion body myositis: an underdiagnosed condition?

The Epidemiology of Neuromuscular Diseases

Neuromuscular disorders as a group are linked by anatomy with significant differences in pathogenetic mechanisms, clinical expression, and time course of disease. Each neuromuscular disease is relatively uncommon, yet causes a significant burden of disease socioeconomically. Epidemiologic studies in different global regions have demonstrated certain neuromuscular diseases have increased incidence and prevalence rates over time. Understanding differences in global epidemiologic trends will aid clinical research and policies focused on prevention of disease. There is a critical need to understand the global impact of neuromuscular diseases using metrics currently established for communicable and noncommunicable diseases.

Lower extremity peak force and gait kinematics in individuals with inclusion body myositis

OBJECTIVE

To determine the relationship between peak isometric muscle force and temporal characteristics of gait in individuals with sporadic inclusion body myositis (s-IBM).

METHODS

An observational study of 42 individuals with s-IBM (12 women; mean ± SD age 61.8 ± 7.3 years and mean ± SD disease duration 8.9 ± 4.3 years) was conducted at a federal hospital. Peak isometric force measurements for lower extremity (LE) muscle groups were obtained using quantitative muscle testing. Temporal characteristics of gait during habitual and fast walking conditions were measured using a portable gait analysis system.

RESULTS

All observed muscle force values were significantly lower than predicted values (P ≤ 0.001). During habitual walking, the subjects' gait speed and cadence were ≤83% of normative literature values. During fast walking, total gait cycle time was 133% of normal, while gait speed and cadence were 58% and 78% of normative literature values, respectively. Scaled LE peak muscle forces showed significant moderate correlations with temporal gait variables. Weaker subjects had greater limitations in gait speed and cadence compared with stronger subjects (P < 0.05). Peak isometric force of the knee flexors and ankle plantar flexors was significantly correlated with most temporal features of habitual gait.

CONCLUSION

Muscle weakness associated with s-IBM disease activity may contribute to diminished gait kinematics. Temporal features of gait were not substantially influenced by knee extensor weakness alone, considering the knee flexors and ankle plantar flexors played a compensatory role in maintaining the walking ability of individuals with s-IBM.

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.

Sporadic-inclusion body myositis (s-IBM) is not so prevalent in Istanbul/Turkey: a muscle biopsy based survey

In a muscle biopsy based study, only 9 out of 5450 biopsy samples, received from all parts of greater Istanbul area, had typical clinical and most suggestive light microscopic sporadic-inclusion body myositis (s-IBM) findings. Two other patients with and ten further patients without characteristic light microscopic findings had referring diagnosis of s-IBM. As the general and the age-adjusted populations of Istanbul in 2010 were 13.255.685 and 2.347.300 respectively, the calculated corresponding 'estimated prevalences' of most suggestive s-IBM in the Istanbul area were 0.679 X 10(-6) and 3.834 X 10(-6). Since Istanbul receives heavy migration from all regions of Turkey and ours is the only muscle pathology laboratory in Istanbul, projection of these figures to the Turkish population was considered to be reasonable and an estimate of the prevalence of s-IBM in Turkey was obtained. The calculated 'estimated prevalence' of s-IBM in Turkey is lower than the previously reported rates from other countries. The wide variation in the prevalence rates of s-IBM may reflect different genetic, immunogenetic or environmental factors in different populations.

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.

Stance control orthosis trial in patients with inclusion body myositis

BACKGROUND

Inclusion Body Myositis (IBM) is an inflammatory myopathy that commonly affects quadriceps strength, resulting in knee buckling and falls. Therefore, patients with IBM should be ideal candidates for stance control orthoses (SCOs).

OBJECTIVES

Evaluate the effectiveness of SCO use in patients with IBM who have functional deficits due to quadriceps weakness.

STUDY DESIGN

Cohort study.

METHODS

Nine subjects with IBM were provided a stance control orthosis and followed for six months of home use. All patients had objective testing of their strength and gait and completed a questionnaire at baseline and six months. Gait analysis was performed both with and without the orthosis.

RESULTS

Velocity and cadence were lower and step width was higher when using the orthosis. Kinematic measures were largely unchanged with orthosis use. Subjects with less knee extensor weakness had a better outcome than weaker participants. Those who spent more time wearing the orthosis also had a more positive outcome. The participants felt that the SCO was helpful in safeguarding against falls and providing stability.

CONCLUSIONS

SCO use will benefit patients with IBM, but care should be taken to choose the SCO option that best suits their individual clinical presentation.

CLINICAL RELEVANCE

This is the first study to examine SCO use in the IBM population. Patients with IBM have quadriceps weakness and will potentially benefit from SCO use. This study suggests that successful SCO management of patients with IBM depends on severity of weakness.

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.

A weak balance: the contribution of muscle weakness to postural instability and falls

Muscle strength is a potentially important factor contributing to postural control. In this article, we consider the influence of muscle weakness on postural instability and falling. We searched the literature for research evaluating muscle weakness as a risk factor for falls in community-dwelling elderly individuals, for evidence that strength training reduces falls, and for pathophysiological evidence from patients with neuromuscular disease that supports the link between muscle weakness and falls. In virtually all studies that included strength testing, muscle weakness was a consistent risk factor for falls in the elderly. Studies that evaluated the merits of muscle strength training often showed a reduction in fall rates, particularly when strength training was a component of a multifactorial intervention, although it was unclear whether strength training alone led to a fall reduction. Surprisingly few studies addressed the pathophysiological relationship between muscle strength and balance control. We conclude that muscle weakness is an important risk factor for falls that is potentially amenable to therapeutic intervention, and that future studies should further clarify the role of muscle weakness in balance control and the pathophysiology of falls.

[Immunocytochemical analysis of the inflammatory infiltrate in inclusion body myositis and other neuromuscular disorders with rimmed vacuoles]

Among 1400 muscle biopsies, we found 16 cases with rimmed vacuoles whose diagnosis were sporadic inclusion body myositis (IBM) (4 cases), juvenile spinal muscular atrophy (6 cases), distal myopathies (3 cases), limb-girdle muscular dystrophy (2 cases), and peripheral neuropathy (1 case). Monoclonal antibodies reactive for T lymphocytes and subsets, B lymphocytes, macrophages, natural killer cells, immunoglobulins, and complement were used to analyze the inflammatory infiltrate. The analysis was quantitative and according to the site of accumulation (interstitial, endomysial, and perivascular). The immunocytochemical analysis showed CD8+ lymphocytes in the interstitial in most cases, occasionally inside of muscle fibers, and rarely in the perivascular region. The IBM cases had an increased number of CD8+ lymphocytes comparing with the other diseases. CD8+/CD4+ ratio was increased in IBM compared with the other diseases. Macrophages were frequent in IBM, distal myopathy, and one case of limb-girdle muscular dystrophy. Natural killer cells were frequent at interstitial.

Inclusion body myositis: investigation of the mumps virus hypothesis by polymerase chain reaction

Inclusion body myositis (IBM) is a distinctive form of chronic inflammatory myopathy characterized pathologically by the finding of rimmed vacuoles and 15-18nm microtubular filamentous inclusions in muscle fiber nuclei and cytoplasm. The observation that these filaments resembled nucleocapsids of the paramyxovirus group and showed immunoreactivity with mumps virus (MV) antibodies has led to a long-standing postulate that IBM may be a "slow" mumps infection. We searched for the presence of MV RNA in 34 muscle biopsies (17 frozen and 17 paraffin-embedded) from 18 patients with IBM and 43 control biopsies (mainly from patients with other forms of inflammatory myopathy) using a polymerase chain reaction (PCR). The MV PCR was shown to be sensitive and specific for MV strains (including J-L) and the integrity of muscle RNA extracts was confirmed by PCR detection of constitutive Ableson tyrosine kinase mRNA. MV RNA was not found in any biopsy from the IBM group nor any of the control cases. Our results therefore do not support the mumps hypothesis for IBM.

Apolipoprotein E epsilon 4 in inclusion body myositis

The genetic predisposition to inclusion body myositis (IBM) is probably multifactorial. The deposition of the beta-amyloid protein is a characteristic histological feature of both IBM and Alzheimer's disease (AD). The epsilon 4 allele of apolipoprotein E (APO E) has been strongly associated with familial and late-onset AD. We therefore compared the APO E allele frequencies in a group of 14 patients with IBM with those in a group of patients with other inflammatory muscle diseases and in the general population. The frequency of the epsilon 4 allele in IBM was increased (0.29) compared with that in patients with other inflammatory muscle diseases (0.15) and the general population (0.13) (p < 0.05). These data suggest that APO E genotype may be one of the factors involved in determining the predisposition to the development of IBM.

HLA associations with inclusion body myositis

Inclusion body myositis (IBM) is defined clinically by a characteristic pattern of progressive proximal and distal limb muscle weakness and resistance to steroid therapy, and histologically by the presence of distinctive rimmed vacuoles and filamentous inclusions as well as a mononuclear infiltrate in which CD8+ T cells are predominant. Muscle damage is believed to be mediated by autoimmune mechanisms, but very little information is available on the immunogenic features of IBM. MHC class I and DR antigens were typed on 13 caucasoid patients with IBM using standard serological techniques or by allele-specific oligonucleotide typing. Complement components C4 and properdin factor B (Bf) were typed by immunofixation after electrophoresis. Restriction fragment length polymorphisms (RFLP) in the class III region were analysed using cDNA probes for C4 and 21-hydroxylase (CYP21) after Taq 1 digestion. IBM was associated with DR3 (92%), DR52 (100%) and HLA B8 (75%). The phenotype data were examined for likely haplotypes by considering together the alleles at the class I, DR and complement loci along with the C4 and CYP21 RFLP. Ten of the DR3+ subjects had a 6.4-kb C4-hybridizing fragment characteristic of a deletion of C4A and CYP21-A. These patients probably carried all, or at least the class II and III regions, of the extended haplotype marked by B8/C4A*Q0/C4B1/BfS/DR3/DR52, which has been associated with several autoimmune diseases and is present in 11% of the healthy caucasoid population. Of the remaining subjects, two had evidence of the extended haplotype marked by B18/C4A3/C4BW*0/BfF1/DR3, which is present in less than 5% of the healthy population and has been associated with insulin-dependent diabetes mellitus. These data provide support for an autoimmune etiology for, and genetic predisposition to, IBM.