Further observations on forearm flexor weakness in inclusion body myositis

Amyotrophic lateral sclerosis mimics

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motor neuron disorder characterized by progressive degeneration of cortical, bulbar, and spinal motor neurons. When a patient presents with a progressive upper and/or lower motor syndrome, clinicians must pay particular attention to any atypical features in the history and/or clinical examination suggesting an alternate diagnosis, as up to 10% percent of patients initially diagnosed with ALS have a mimic of ALS. ALS is a clinical diagnosis and requires the exclusion of other disorders that may have similar presentations but a more favorable prognosis or an effective therapy. Because there is currently no specific diagnostic biomarker that is sensitive or specific for ALS, understanding the spectrum of clinical presentations of ALS and its mimics is paramount. While true mimics of ALS are rare, the clinician must correctly identify these disorders to avoid the misdiagnosis of ALS and to initiate effective treatment where available.

Myopathies with finger flexor weakness: Not only inclusion-body myositis

Muscle disorders are characterized by differential involvement of various muscle groups. Among these, weakness predominantly affecting finger flexors is an uncommon pattern, most frequently found in sporadic inclusion-body myositis. This finding is particularly significant when the full range of histopathological findings of inclusion-body myositis is not found on muscle biopsy. Prominent finger flexor weakness, however, is also observed in other myopathies. It occurs commonly in myotonic dystrophy types 1 and 2. In addition, individual reports and small case series have documented finger flexor weakness in sarcoid and amyloid myopathy, and in inherited myopathies caused by ACTA1, CRYAB, DMD, DYSF, FLNC, GAA, GNE, HNRNPDL, LAMA2, MYH7, and VCP mutations. Therefore, the finding of finger flexor weakness requires consideration of clinical, myopathological, genetic, electrodiagnostic, and sometimes muscle imaging findings to establish a diagnosis.

Inclusion body myositis: clinical features and pathogenesis

Inclusion body myositis (IBM) is often viewed as an enigmatic disease with uncertain pathogenic mechanisms and confusion around diagnosis, classification and prospects for treatment. Its clinical features (finger flexor and quadriceps weakness) and pathological features (invasion of myofibres by cytotoxic T cells) are unique among muscle diseases. Although IBM T cell autoimmunity has long been recognized, enormous attention has been focused for decades on several biomarkers of myofibre protein aggregates, which are present in <1% of myofibres in patients with IBM. This focus has given rise, together with the relative treatment refractoriness of IBM, to a competing view that IBM is not an autoimmune disease. Findings from the past decade that implicate autoimmunity in IBM include the identification of a circulating autoantibody (anti-cN1A); the absence of any statistically significant genetic risk factor other than the common autoimmune disease 8.1 MHC haplotype in whole-genome sequencing studies; the presence of a marked cytotoxic T cell signature in gene expression studies; and the identification in muscle and blood of large populations of clonal highly differentiated cytotoxic CD8⁺ T cells that are resistant to many immunotherapies. Mounting evidence that IBM is an autoimmune T cell-mediated disease provides hope that future therapies directed towards depleting these cells could be effective.

[Usefulness of rehabilitation in inflammatory myopathies]

Rehabilitation, for a long time not recommended, seems today to hold a prominent place within the therapeutic arsenal of inflammatory myopathies. The difficulty of its evaluation, apart from the low prevalence of these diseases, lies in a triple heterogeneity: first that distinguishing the different forms of inflammatory myopathies and the phase where they are active; second, that concerning the endpoint considered to assess the efficiency of the intervention; lastly, the diversity of the rehabilitation programs that can be undertaken. Between 1993 and 2016, about 30 studies estimating the rehabilitation of inflammatory myopathies have been published, among which five randomized controlled trials, four controlled trials, 15 open studies, and seven case reports. All these studies evidence the safety of rehabilitation and some show a significant improvement of the criteria estimating the activity of the disease, its functional impact or the impairment of quality of life and the limitation in daily life activities triggered by the disease. The rehabilitation, whether aerobic, anaerobic or mixed, must today systematically be associated with the pharmaceutic treatment proposed to patients affected by inflammatory myopathies. Other studies are necessary to optimize the rehabilitation methods, to understand their effects and action, and to quantify their impact and provide more trustworthy evidence.

Pathogenesis and therapy of inclusion body myositis

PURPOSE OF REVIEW

Inclusion body myositis (IBM) is a poorly understood progressive muscle disease of middle and later life. Its dual pathologies of autoimmunity and unexplained myofiber degeneration and loss have been enigmatic since its earliest descriptions over 40 years ago. No reliable effective therapy currently exists for IBM. This review provides an update of current issues in the pathogenesis and therapy of IBM.

RECENT FINDINGS

Recent studies have further defined the clinical features of IBM, including natural history, pattern of muscle involvement, and role of MRI imaging. Further potential immune mediators have been identified. An autoantibody directed against a muscle antigen appears to have high specificity for IBM among muscle diseases. Further evidence for myonuclear degeneration has been reported.

SUMMARY

IBM remains a poorly understood muscle disease, although understanding of the pathophysiological mechanisms continues to expand and is supporting new therapeutic approaches.

Inclusion body myositis

PURPOSE OF REVIEW

Sporadic inclusion body myositis (sIBM) is a poorly understood immune and degenerative disease of skeletal muscle. Here, current opinion of the nature of this disease is summarized.

RECENT FINDINGS

Recent findings for sIBM include further characterization of muscle involvement through magnetic resonance imaging, the role of muscle as a host for immune cells, progress in the role of extranuclear TDP-43 in causing cellular injury, and the discovery of a new sIBM autoantibody.

SUMMARY

sIBM understanding continues to advance, with progress regarding the mechanism of this disease.

Inclusion body myositis: current pathogenetic concepts and diagnostic and therapeutic approaches

Inclusion body myositis is the most common acquired muscle disease in older individuals, and its prevalence varies among countries and ethnic groups. The aetiology and pathogenesis of sporadic inclusion body myositis are still poorly understood; however genetic factors, ageing, and environmental triggers might all have a role. Unlike other inflammatory myopathies, sporadic inclusion body myositis causes slowly progressing muscular weakness and atrophy, it has a distinctive pattern of muscle involvement, and is unresponsive to conventional forms of immunotherapy. This review covers the clinical presentation, diagnosis, treatment, and the latest information on genetic susceptibility and pathogenesis of sporadic inclusion body myositis.

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.

The role of exercise in the rehabilitation of idiopathic inflammatory myopathies

PURPOSE OF REVIEW

The objective of this review is to provide an update on exercise and clinical assessment in the idiopathic inflammatory myopathies.

RECENT FINDINGS

Polymyositis, dermatomyositis and inclusion body myositis are rare conditions with muscle weakness as a common prominent feature. Earlier, these patients were discouraged from active exercise due to a fear of increased muscle inflammation with recommendations to rest, perform range of motion exercises and in some cases, isometric exercises. However, beginning in the 1990s, studies reported reduced disability in patients with chronic polymyositis/dermatomyositis following resistive mild/moderate to intensive muscular training and aerobic endurance training, without signs of increased muscle inflammation. Patients with active, recent onset disease seem to benefit from mild/moderate muscular exercise without signs of increased muscle inflammation. There is no evidence of increased muscle inflammation following exercise in inclusion body myositis. However the beneficial effects are unclear as one study report increased muscle strength, while the other could not achieve impairment reduction.

SUMMARY

Studies evaluating active exercise in IIM support the notion of safety and benefits. However, large multi-center studies are needed to fully establish the safety and benefits of different types of exercise. Data indicate that active exercise, adapted to disease activity and disability should be included in the rehabilitation of patients in all stages of IIM. The newly developed and validated outcome measures for patients with polymyositis and dermatomyositis help assess the effects of interventions on disease activity and disability in clinical trials and in clinical practice. However, there are no sensitive and valid outcome measure for patients with inclusion body myositis.

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.

Inclusion body myositis

Sporadic inclusion body myositis is a severely disabling muscle disease that mainly affects elderly individuals. The typical distribution of muscle weakness, poor response to immunosuppressive treatment, pathological accumulation of various proteins in vacuolated muscle fibres, inflammatory reaction and mitochondrial changes have all been subjects of recent research that has led to better understanding of the pathogenic events that leads to muscle degeneration and weakness.