From the Guidelines
The diagnostic approach for myositis should involve a comprehensive evaluation combining clinical assessment, laboratory testing, imaging, and often muscle biopsy, with a focus on identifying muscle inflammation and guiding treatment selection, as recommended by the most recent and highest quality study 1. The diagnostic approach for myositis involves several key steps, including:
- Clinical assessment: evaluating muscle weakness patterns, skin changes, and systemic symptoms
- Laboratory testing: measuring creatine kinase (CK), aldolase, AST, ALT, and LDH, as well as inflammatory markers such as ESR and CRP 1
- Imaging: using MRI to identify muscle inflammation and guide biopsy sites, with T1-weighted, T2-weighted, and fat suppression techniques providing useful information 1
- Muscle biopsy: remaining the gold standard for diagnosis, revealing inflammatory infiltrates, fiber degeneration, and regeneration
- Additional testing: including chest imaging to assess for interstitial lung disease, particularly in antisynthetase syndrome, and skin biopsy for dermatomyositis This systematic approach allows for accurate diagnosis, classification of myositis subtype, and guides appropriate treatment selection, with the goal of improving morbidity, mortality, and quality of life outcomes for patients with myositis, as emphasized by recent studies 1. Key diagnostic tools include:
- Electromyography (EMG) to show characteristic myopathic changes with spontaneous fibrillations
- Myositis-specific antibodies (MSAs) like anti-Jo-1, anti-Mi-2, and anti-SRP to classify subtypes and predict disease course
- MRI to identify muscle inflammation and guide biopsy sites, with fasciitis frequently reported on MRI in cases of IR-myositis 1.
From the Research
Diagnostic Approach for Myositis
The diagnostic approach for myositis involves a combination of clinical assessment, laboratory investigations, and muscle biopsy.
- Clinical features are distinct for each subtype of myositis, including dermatomyositis (DM), polymyositis (PM), necrotizing myopathy (NM), and inclusion body myositis (IBM) 2.
- A thorough clinical assessment, including a detailed family history, is essential in evaluating patients with presumed idiopathic inflammatory myopathy 3.
- Laboratory investigations, such as electromyography and creatine kinase measurements, should be undertaken to support the diagnosis 3.
- Muscle biopsy remains essential in achieving an accurate diagnosis and guiding treatment 2, 3.
- The use of magnetic resonance imaging (MRI) of skeletal muscles and detection of myositis-specific autoantibodies have become useful additions to the diagnostic repertoire 2.
- Plasma CK concentrations, total CK and CK-MB serum concentrations, and serum concentrations of aspartate aminotransferase can be used as muscle enzyme markers for diagnosis and progression of myositis 4.
Importance of Accurate Diagnosis
Accurate diagnosis is crucial before commencing immunosuppressive treatment, as the potential toxicity associated with these regimens can be significant 3.
- A precise tissue diagnosis confirming features of an active inflammatory process should be achieved before immunosuppressive treatment is commenced 3.
- Close collaboration between clinicians and muscle pathologists is essential in allowing the most accurate interpretation of myopathologic findings in the clinical context 3.
- A high level of clinical suspicion is needed in the diagnosis of focal myositis, a rare and uncommon cause of cervical mass 5.