From the Guidelines
The diagnosis of autoimmune myositis should be based on the 2017 European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria, which provide a score with a corresponding probability of having idiopathic inflammatory myopathy (IIM) 1. The EULAR/ACR criteria are data-driven, exhibit high sensitivity and specificity, and use a limited number of accessible, defined clinical and laboratory variables. Key features of the diagnosis include:
- Clinical evaluation for symptoms and signs of myositis, such as muscle weakness and skin rash
- Laboratory testing for muscle enzymes, including creatine kinase (CK), aldolase, AST, ALT, and LDH, which are typically elevated in active disease
- Autoantibody testing, including myositis-specific antibodies (anti-Jo-1, anti-Mi-2, anti-SRP) and myositis-associated antibodies
- Imaging studies, such as MRI, to identify muscle inflammation and guide biopsy sites
- Muscle biopsy, which remains the gold standard for diagnosis, revealing inflammatory infiltrates, muscle fiber degeneration, and regeneration The EULAR/ACR criteria demonstrated sensitivity and specificity of 87% and 82%, respectively, with even higher accuracy when muscle biopsies were included, 93% and 88%, respectively 1. Additional testing should include screening for associated malignancies, particularly in dermatomyositis patients over 40, with age-appropriate cancer screening and consideration of CT chest/abdomen/pelvis, as well as pulmonary function tests and high-resolution CT of the chest to assess for interstitial lung disease 1. Early diagnosis is essential as prompt immunosuppressive therapy can prevent irreversible muscle damage and improve outcomes. It is also important to consider the patient's clinical presentation, medical history, and other diagnostic criteria, such as the presence of myositis-specific autoantibodies, to guide the diagnosis and management of autoimmune myositis.
From the Research
Diagnosis of Autoimmune Myositis
The diagnosis of autoimmune myositis involves a combination of clinical examination, laboratory tests, and imaging studies. Some key points to consider include:
- The use of myositis-specific autoantibodies to help diagnose and classify the condition 2, 3, 4
- The importance of muscle biopsy in making a reliable diagnosis, although it may not be necessary in all cases 5, 3
- The use of magnetic resonance imaging (MRI) of skeletal muscles to aid in diagnosis 5
- The need for a thorough clinical examination and interrogation to identify clinical features and symptoms 3
- The use of electromyographic data and immunological testing to support the diagnosis 3
Classification of Autoimmune Myositis
Autoimmune myositis can be classified into several subtypes, including:
- Dermatomyositis (DM) 2, 5, 3, 4
- Polymyositis (PM) 2, 5, 3, 4
- Inclusion body myositis (IBM) 2, 5, 3
- Immune-mediated necrotizing myopathy (IMNM) 2, 3
- Antisynthetase syndrome (ASS) 2, 3
- Overlapping myositis 3
Diagnostic Tools
Several diagnostic tools are available to aid in the diagnosis of autoimmune myositis, including: