polymyositis — LLMpedia

polymyositis
Name	Polymyositis
Field	Rheumatology, Neurology, Immunology
Symptoms	Proximal muscle weakness, dysphagia, myalgia
Complications	Interstitial lung disease, cardiac involvement, malignancy associations
Onset	Adulthood
Duration	Chronic
Causes	Autoimmune processes
Diagnosis	Clinical evaluation, elevated CK, EMG, MRI, muscle biopsy
Treatment	Corticosteroids, immunosuppressants, physical therapy

Contents

polymyositis

Introduction

Polymyositis is an inflammatory myopathy characterized by chronic, symmetric proximal muscle weakness affecting axial and limb girdle muscles. Historically described in clinical reports from European centers and continental hospitals, it has been studied in cohorts linked to institutions such as Mayo Clinic, Johns Hopkins Hospital, Massachusetts General Hospital, Charité – Universitätsmedizin Berlin, Royal Free Hospital, Hôpital Pitié-Salpêtrière, Cleveland Clinic, and Guy's Hospital. Research into its immunopathogenesis has involved collaborations with organizations like the National Institutes of Health, Wellcome Trust, European League Against Rheumatism, American College of Rheumatology, World Health Organization, and the European Medicines Agency.

Patients typically present with gradually progressive, symmetric proximal muscle weakness causing difficulty rising from a chair, climbing stairs, or lifting objects, as described in case series from Mount Sinai Hospital, UCSF Medical Center, Penn Medicine, Royal Melbourne Hospital, Hospital for Special Surgery, and Karolinska University Hospital. Extra-muscular manifestations include dysphagia, respiratory compromise, and arthralgia reported in cohorts from Toronto General Hospital, St Bartholomew's Hospital, Toronto Western Hospital, and St Thomas' Hospital, and systemic features have been detailed in registries maintained by National Health Service (England), Centers for Disease Control and Prevention, and European Rare Disease Network. Cardiac conduction abnormalities and myocarditis have been documented in case series from Cedars-Sinai Medical Center, The Alfred Hospital, Sunnybrook Health Sciences Centre, and Royal Prince Alfred Hospital. Cutaneous findings are less prominent than in dermatomyositis but overlap syndromes with skin involvement have been reported by teams at Guy's and St Thomas NHS Foundation Trust, Sheffield Teaching Hospitals, and King's College Hospital.

Polymyositis is considered an autoimmune-mediated myositis with cytotoxic CD8+ T lymphocyte infiltration targeting muscle fibers, a mechanism elaborated in basic science studies at Max Planck Institute for Immunobiology and Epigenetics, Institut Pasteur, Salk Institute, and Francis Crick Institute. Genetic susceptibility loci identified in association studies have involved alleles studied at Broad Institute, Wellcome Sanger Institute, Harvard Medical School, and University of Oxford. Viral triggers and molecular mimicry hypotheses have been evaluated following outbreaks and case clusters investigated by Centers for Disease Control and Prevention, European Centre for Disease Prevention and Control, Public Health England, and Health Canada. Paraneoplastic associations and links to malignancies were examined in oncology collaborations at Memorial Sloan Kettering Cancer Center, MD Anderson Cancer Center, Royal Marsden Hospital, and Institut Curie, with epidemiological analyses from Surveillance, Epidemiology, and End Results Program and National Cancer Institute datasets. Immunologic pathways involving major histocompatibility complex class I upregulation, interferon signatures, cytokines, and complement components have been characterized in laboratories at Dana-Farber Cancer Institute, Vanderbilt University Medical Center, Johns Hopkins University School of Medicine, and Columbia University Irving Medical Center.

Diagnostic evaluation integrates clinical assessment with laboratory and instrumental testing as outlined in guidelines from American College of Rheumatology, European League Against Rheumatism, British Society for Rheumatology, Japanese Society of Neurology, and consensus statements from networks such as International Myositis Assessment and Clinical Studies Group. Serum creatine kinase elevation is commonly reported in datasets from Mayo Clinic, Cleveland Clinic, Karolinska University Hospital, and Oslo University Hospital. Electromyography abnormalities and muscle MRI edema patterns have been described in publications from Massachusetts General Hospital, Hospital for Sick Children (Toronto), Singapore General Hospital, and Seoul National University Hospital. Muscle biopsy demonstrating endomysial inflammation with CD8+ T cells and fiber necrosis remains a gold standard in pathology series from Royal Brompton Hospital, Addenbrooke's Hospital, Mount Sinai, and University College London Hospitals. Autoantibody profiles, including myositis-specific antibodies studied at National Institutes of Health, Laboratoire de Référence René Huguenin, and Institut de Myologie, assist in subclassification and prognosis.

First-line therapy typically comprises high-dose corticosteroids with steroid-sparing immunosuppressants and biologic agents employed in refractory cases, following protocols tested at Mayo Clinic, Cleveland Clinic, Johns Hopkins Hospital, Massachusetts General Hospital, Hospital for Special Surgery, Charité – Universitätsmedizin Berlin, and trial sites coordinated by National Institutes of Health and European Medicines Agency-sponsored studies. Common steroid-sparing agents include azathioprine, methotrexate, mycophenolate mofetil, and calcineurin inhibitors, with usage described in therapeutic series from UCLA Health, Mount Sinai Hospital, St Vincent's Hospital (Sydney), and The Royal Children's Hospital Melbourne. Intravenous immunoglobulin and rituximab have been evaluated in randomized and open-label trials conducted at University of Oxford, Imperial College London, Hospital Clínic de Barcelona, Hospital Universitario La Paz, and Universitätsklinikum Freiburg. Supportive care involving physiotherapy, occupational therapy, respiratory support, and nutritional management is emphasized by multidisciplinary teams at Great Ormond Street Hospital, Sheba Medical Center, Johns Hopkins Children's Center, and Royal Children's Hospital (Melbourne).

Prognosis varies: some patients achieve remission with therapy while others develop chronic disability, as shown in long-term cohorts from Mayo Clinic, Karolinska University Hospital, Seoul National University Hospital, Toronto General Hospital, and Addenbrooke's Hospital. Complications include interstitial lung disease, respiratory failure, cardiac involvement, and increased malignancy risk noted in registries compiled by National Cancer Institute, Swedish National Patient Register, National Health Service (England), and Danish National Patient Registry. Mortality predictors and quality-of-life outcomes have been reported in analyses from European League Against Rheumatism, American College of Rheumatology, World Health Organization, Centers for Disease Control and Prevention, and university medical centers such as Johns Hopkins Hospital, Massachusetts General Hospital, and Mayo Clinic.

Category:Inflammatory myopathies