What does autoimmune myositis (inflammatory muscle disease) blood work results indicate?

From the Guidelines

Autoimmune myositis blood work results indicate the presence of myositis-specific autoantibodies, muscle enzymes, and inflammatory markers that help diagnose and classify inflammatory muscle diseases, guiding treatment decisions and monitoring disease activity over time. The blood work typically includes muscle enzymes like creatine kinase (CK) and aldolase, which are elevated when muscle damage occurs 1. Myositis-specific antibodies such as anti-Jo-1, anti-Mi-2, anti-SRP, anti-HMGCR, and anti-TIF1-gamma are also included, as they are associated with different subtypes of myositis and can suggest specific extramuscular organ involvement and prognosis 1. Some key points to consider when interpreting autoimmune myositis blood work results include:

• Myositis-specific autoantibodies can define subgroups of patients with idiopathic inflammatory myositis and suggest specific extramuscular organ involvement, such as the pulmonary and cardiac systems 1
• The presence of certain autoantibodies, such as anti-Jo-1, can be associated with specific clinical features, such as mechanic’s hands, arthritis, and interstitial lung disease (ILD) 1
• Inflammatory markers like erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are measured to assess overall inflammation levels 1
• Complete blood count, comprehensive metabolic panel, and tests for other autoimmune conditions may be included to rule out alternative diagnoses or identify overlapping disorders 1
• Novel biomarkers of disease activity, such as interleukin 6 and type 1 interferon-regulated genes, may serve as indicators of disease activity in adult and juvenile myositis 1 It is essential to note that blood work alone is not sufficient for diagnosis, and clinical symptoms, muscle strength testing, electromyography, and sometimes muscle biopsy are needed for a complete evaluation 1.

From the Research

Autoimmune Myositis Blood Work Results

Autoimmune myositis, also known as inflammatory muscle disease, is characterized by the presence of autoantibodies that play a crucial role in the disease phenotype. The blood work results for autoimmune myositis may indicate the presence of myositis-specific autoantibodies (MSAs) and myositis-associated autoantibodies (MAAs) 2, 3, 4.

• Myositis-specific autoantibodies (MSAs) are found in 25-50% of patients with polymyositis (PM) and dermatomyositis (DM) and are associated with specific clinical features and prognosis 2.
• The presence of anti-signal recognition particle (SRP) antibody is associated with severe myopathy and highly elevated serum creatine kinase levels 5.
• Anti-synthetase antibodies, such as anti-Jo-1, are associated with anti-synthetase syndrome, characterized by myositis, interstitial lung disease, arthritis, and Raynaud's phenomenon 3.
• Other MSAs, such as anti-Mi-2, anti-TIF1γ/α, and anti-MDA5, are associated with specific clinical features and prognosis in DM 3, 4.

Clinical Significance of Autoantibodies

The presence of autoantibodies in autoimmune myositis has significant clinical implications, including:

• Diagnosis: Autoantibodies can help support the diagnosis of myositis and exclude other conditions, such as inclusion body myositis 2.
• Prognosis: Certain autoantibodies, such as anti-SRP, are associated with a poor prognosis and treatment-resistant myopathy 5, 2.
• Treatment: The presence of autoantibodies can guide treatment decisions, such as the use of immunosuppressive therapy 5, 6.

Laboratory Findings

Laboratory findings in autoimmune myositis may include:

• Elevated serum creatine kinase levels, indicating muscle damage 5, 6.
• Presence of myositis-specific autoantibodies, such as anti-SRP, anti-Jo-1, and anti-Mi-2 5, 2, 3.
• Abnormal muscle biopsy findings, such as increased sarcolemmal major histocompatibility complex class I (MHC1) expression and vascular membrane attack complex (C5b-9) deposition 6.