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Dermatomyositis and polymyositis
Background
Overview
Definition
DM/PM are autoimmune myopathies characterized by subacute or chronic inflammation and weakness of proximal muscles with extra muscular manifestations.
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Pathophysiology
Dermatomyositis is mostly caused by humoral immune response whereas polymyositis is caused by T cell-mediated immune response.
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Disease course
Autoimmunity results in polymyositis (PM) and dermatomyositis (DM), which cause clinical manifestations of symmetrical proximal muscle weakness, pain, inflammation, typical rash in DM, fever, non-erosive arthritis, hyperkeratotic lesions along the radial and palmar aspects of fingers. Disease progression may lead to ILD and increased risk of malignancy.
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Prognosis and risk of recurrence
The in-hospital mortality rate of DM/PM is 4.58%.
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Guidelines
Key sources
The following summarized guidelines for the evaluation and management of dermatomyositis and polymyositis are prepared by our editorial team based on guidelines from the American College of Rheumatology (ACR 2023), the European League Against Rheumatism (EULAR 2023), the British Society for Rheumatology (BSR 2022), and the Japan College of Rheumatology (JCR 2019).
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Classification and risk stratification
Diagnostic investigations
Initial evaluation: as per JCR 2019 guidelines, measure anti-aminoacyl-tRNA synthetases (ARS) antibodies - including anti‐Jo‐1 and other specific autoantibodies - in patients with DM/PM, as they are closely associated with clinical subsets, pathogenesis, clinical course and therapeutic responsiveness of patients with myositis.
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Antibody testing
Assessment of disease activity
Evaluation for cardiac involvement
Evaluation for dysphagia
Bone health assessment
Mental health assessment
Screening for chronic infections
Medical management
General principles: as per JCR 2019 guidelines, consider treating malignancy, if present concomitantly with DM/PM, as the first step in management, unless the symptoms of DM/PM require urgent treatment.
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Corticosteroids
Immunosuppressants
Biologics
IVIG
Management of cutaneous manifestations
Management of dysphagia
Management of ILD
Management of cardiac myositis
Management of relapse
Nonpharmacologic interventions
Sun protection: as per BSR 2022 guidelines, consider advising sun avoidance and regular use of high factor broad spectrum sun cream to reduce likelihood of a disease flare affecting skin or muscle.
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Physiotherapy
Specific circumstances
Pediatric patients, evaluation: as per BSR 2022 guidelines, take age-specific considerations into account when using tools measuring muscle strength, function, and QoL.
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Pregnant patients
Pediatric patients (specialist referral)
Pediatric patients (corticosteroids and immunosuppressants)
Pediatric patients (management of cutaneous manifestations)
Pediatric patients (physiotherapy)
Preventative measures
Routine immunizations: as per ACR 2023 guidelines, consider offering high-dose or adjuvanted influenza vaccination, rather than regular-dose influenza vaccination, in ≥ 65 years old patients with rheumatic or musculoskeletal diseases and in 18-65 years old patients with rheumatic or musculoskeletal diseases on immunosuppressive medications.
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Prophylaxis for P. jirovecii pneumonia
Follow-up and surveillance
Surveillance for malignancy: as per BSR 2022 guidelines, take into account the risk of cancer in all patients and consider screening particularly in patients with the following risk factors:
older age at onset
male gender
dysphagia
cutaneous necrosis
resistance to immunosuppressive therapy
rapid disease onset
positive anti-TIF-1-gamma autoantibodies
positive anti-nuclear matrix protein-2 autoantibodies
negative for known myositis-specific autoantibodies.
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