Myositis mimics: how to recognize them

Idiopathic inflammatory myopathies: state of the art on clinical practice guidelines [corrected]

Idiopathic inflammatory myopathies (IIMs) encompass a heterogeneous group of rare autoimmune diseases characterised by muscle weakness and inflammation, but in antisynthetase syndrome arthritis and interstitial lung disease are more frequent and often inaugurate the disease. Clinical practice guidelines (CPGs) have been proposed for IIMs, but they are sparse and heterogeneous. This work aimed at identifying: i) current available CPGs for IIMs, ii) patients ' and clinicians' unmet needs not covered by CPGs. It has been performed in the framework of the European Reference Network on rare and complex connective tissue and musculoskeletal diseases (ReCONNET), a network of centre of expertise and patients funded by the European Union's Health Programme. Fourteen original CPGs were identified, notably recommending that: i) extra-muscular involvements should be assessed; ii) corticosteroids and methotrexate or azathioprine are first-line therapies of IIMs. ii) IVIG is a treatment of resistant-DM that may be also used in other resistant-IIMs; iii) physical therapy and sun protection (in DM patients) are part of the treatment; v) tumour screening for patients with DM include imaging of chest, abdomen, pelvis and breast (in woman) along with colonoscopy (in patients over 50 years); vi) disease activity and damages should be monitor using standardised and validated tools. Yet, only half of these CPGs were evidence-based. Crucial unmet needs were identified both by patients and clinicians. In particular, there was a lack of large multidisciplinary working group and of patients ' preferences. The following fields were not or inappropriately targeted: diagnosis; management of extra-muscular involvements other than skin; co-morbidities and severe manifestations.

Strategy for suspected myositis

Skeletal muscle inflammation is the feature shared by all forms of myositis. However, the muscle damage ranges in severity from asymptomatic to responsible for severe weakness. In addition, myositis usually occurs as a systemic disease that affects multiple organs. More specifically myositis should be considered in patients with muscular, cutaneous, pulmonary, and articular manifestations. The definitive diagnosis and classification of myositis has benefited considerably in recent years from the identification of characteristic autoantibodies. Nonetheless, a muscle biopsy is often necessary to confirm the diagnosis, and the differential diagnoses may raise challenges that require evaluation at a myositis referral center. The management depends on the type of myositis. Treatments should be provided for both the systemic complications (involving the lungs, heart, gastrointestinal tract, and/or joints) and the comorbidities (cancer and risks factors for cardiovascular disease, thromboembolism, and fractures), which together determine the prognosis. Many drugs are available for treating myositis. Findings from randomized controlled trials will help to use them optimally.

Metabolic myopathies: a practical approach

Metabolic myopathies are a diverse group of rare genetic disorders and their associated muscle symptoms may be subtle. Patients may present with indolent myopathic features, exercise intolerance or recurrent rhabdomyolysis. Diagnostic delays are common and clinicians need a high index of suspicion to recognise and differentiate metabolic myopathies from other conditions that present in a similar fashion. Standard laboratory tests may be normal or non-specific, particularly between symptomatic episodes. Targeted enzyme activity measurement and next-generation genetic sequencing are increasingly used. There are now specific enzyme replacement therapies available, and other metabolic strategies and gene therapies are undergoing clinical trials. Here, we discuss our approach to the adult patient with suspected metabolic myopathy. We outline key features in the history and examination and discuss some mimics of metabolic myopathies. We highlight some disorders of glycogen and fatty acid utilisation that present in adulthood and outline current recommendations on management.

Inflammatory myopathies: A new landscape

Greater accuracy in clinical descriptions combined with advances in muscle histology and immunology have established that inflammatory myopathies (IMs), similarly to inflammatory rheumatic diseases, constitute a highly heterogeneous group of conditions. The topographic distribution, severity, and tempo of onset of the myopathy vary widely, and the histological findings distinguish at least five different profiles, which may reflect different pathophysiological processes. Most IMs are connective tissue diseases that can affect multiple organs, among which the most common targets are the skin, joints, and lungs. The extramuscular manifestations may antedate the muscular involvement and should therefore suggest a diagnosis of IM even in the absence of obvious muscle disease. About 20 different autoantibodies have been identified in patients with IM. Some are mutually exclusive and associated with specific combinations of clinical manifestations. Following the model of antisynthetase syndrome, about 10 syndromes associated with autoantibodies specific of IM have been identified. Thus, polymyositis is now emerging as a rare entity that is often mistaken for more recently described patterns of IM. No consensus exists to date about the classification of IMs. Nevertheless, the clinical manifestations, autoantibody profile, and muscle histology can be used to distinguish patient subgroups with fairly homogeneous patterns of complications, treatment responses, and outcomes. These subgroups are also characterized by specific genetic and environmental factors. The advances made in the nosology of IMs have benefited the diagnosis, personalization of treatment strategies, and understanding of pathophysiological mechanisms. They can be expected to assist in the development of specific treatments.

Polymyositis without Beneficial Response to Steroid Therapy: Should Miyoshi Myopathy be a Differential Diagnosis?

Patient: Male, 16

Final Diagnosis: Miyoshi myopathy

Symptoms: HyperCKemia • myalgia • weakness

Medication: —

Clinical Procedure: —

Specialty: Neurology

[Inflammatory myopathies]

Inflammatory myopathies comprise heterogeneous, often multisystemic autoimmune diseases with muscle involvement as a common feature. The prognosis largely depends on a timely diagnosis and initiation of therapy. Given the complexity of these rare diseases, when an inflammatory myopathy is suspected patients should be referred to an expert center with established algorithms for the diagnostic work-up. The differential diagnostic exclusion of myositis mimics should ideally be carried out in close collaboration with neurologists and neuropathologists. The choice of immunosuppressive treatment should primarily depend on disease severity and organ involvement but age and comorbidities also have to be taken into account.

Selected aspects of the current management of myositis

The idiopathic inflammatory myopathies (IIM) are a rare and heterogeneous group of acquired autoimmune muscle disorders, often referred to as 'myositis'. Clinical assessment, together with muscle biopsy findings and autoantibody status are key factors to consider when making a diagnosis of IIM, and in stratification of the 'IIM spectrum' into disease subgroups. Treatment stratified according to serotype (and in the future, likely also genotype) is increasingly being used to take account of the heterogeneity within the IIM spectrum. Subgroup classification is also important in terms of monitoring for complications, such as malignancy and interstitial lung disease. Disease monitoring should include the use of standardized tools such as the IMACS disease activity outcome measures. Other tools such as muscle MRI can be useful in identifying areas of active muscle inflammation. Treatment outcomes in IIM remain unsatisfactory. The evidence base to guide treatment decisions is remarkably limited. In addition to muscle inflammation, a number of noninflammatory cell-mediated mechanisms may contribute to weakness and disability, and for which no specific treatments are currently available.

Causes of creatine kinase levels greater than 1000 IU/L in patients referred to rheumatology

Patients with severely elevated creatine kinase (CK) concentrations are commonly referred to rheumatologists to evaluate for the presence of an idiopathic inflammatory myopathy (IIM). However, no studies have evaluated the frequency with which IIMs are encountered in this clinical scenario. The Vanderbilt Synthetic Derivative, a de-identified copy of over 2 million patient records, was searched to identify adult patients with a CK greater than 1000 IU/L who had been evaluated by a rheumatologist. Each patient was assigned a diagnosis using a pre-determined algorithm. The records were then reviewed for pertinent demographic data and clinical characteristics. A total of 192 patients were included for analysis. Of these patients, 105 (55 %) were diagnosed with an IIM. The non-IIM causes were drug/toxin exposure (n = 16, 8 %), infection (n = 12, 6 %), trauma (n = 10, 5 %), myocardial injury (n = 5, 3 %), hypothyroidism (n = 4, 2 %), muscular dystrophy (n = 4, 2 %), neuropsychiatric disorder (n = 3, 2 %), metabolic myopathy (n = 2, 1 %), idiopathic CK elevation (n = 11, 6 %), and other diagnoses (n = 20, 10 %). Several characteristics were found to be significantly different between IIM and non-IIM cases. In particular, patients with an IIM were more likely to be female, have a positive ANA, have interstitial lung disease, and have proximal, symmetric weakness. This study found that approximately half of patients referred to our division of rheumatology with a CK greater than 1000 IU/L were diagnosed with an IIM. Given the importance of prompt diagnosis and treatment of these disorders, rapid assessment by the consulting rheumatologist for these patients is recommended.

An overview of muscle diseases presenting in adulthood

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