What is the workup for muscle pain (myalgia)?

From the Guidelines

The workup for myalgia should include a complete rheumatologic and neurologic history, examination of muscle strength, and blood testing to evaluate muscle inflammation, as recommended by the American Society of Clinical Oncology clinical practice guideline 1. The diagnostic work-up should comprise the following key components:

• A thorough history and physical examination to identify potential causes and consider preexisting conditions that can cause similar symptoms
• Blood testing, including:
  • Creatine kinase (CK) to assess muscle damage
  • Transaminases (AST, ALT), lactate dehydrogenase (LDH), and aldolase to evaluate muscle inflammation
  • Troponin to evaluate myocardial involvement
  • Inflammatory markers (ESR and CRP) to assess for inflammation
• Additional testing, such as electromyography (EMG), imaging (MRI), and/or biopsy, may be considered on an individual basis when diagnosis is uncertain or overlap with neurologic syndromes is suspected 1. It is essential to tailor the workup to the clinical presentation, considering medication review and potential systemic conditions, such as polymyalgia rheumatica, fibromyalgia, and viral infections, based on accompanying symptoms. The American Society of Clinical Oncology clinical practice guideline recommends monitoring CK, ESR, and CRP levels to assess treatment response and disease progression 1.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Diagnostic Approach for Myalgia

The diagnostic approach for myalgia involves a combination of laboratory tests, physical examinations, and medical history.

• Initial screening tests include creatine kinase and erythrocyte sedimentation rate (ESR) 2
• If either of these tests is abnormal, further investigations such as muscle biopsy, electromyography, muscle strength, and exercise testing may be performed 2
• Other laboratory tests that may be useful in diagnosing myalgia include C-reactive protein (CRP) and interleukin-6 levels 3

Specific Conditions that May Cause Myalgia

Several specific conditions may cause myalgia, including:

• Post-infection myositis, which may occur after a viral infection and is characterized by severe myalgia and muscle weakness in the proximal muscles of the lower limbs 3
• Polymyalgia rheumatica (PMR), a common inflammatory disorder characterized by myalgia and stiffness in the proximal hip and shoulder girdle, elevated CRP and ESR, and normal creatine kinase levels 4, 5
• Muscle vasculitis, which may be an underlying pathology in PMR, particularly in refractory cases 4
• Adult-onset Still's disease (AOSD), a condition that may mimic myositis and is characterized by severe myalgia, progressive weakness, and elevated serum ferritin levels 6

Laboratory Tests and Diagnostic Criteria

Laboratory tests and diagnostic criteria for myalgia may vary depending on the underlying condition.

• Elevated CRP and ESR levels are common in many conditions that cause myalgia, including PMR and AOSD 3, 4, 6, 5
• Normal creatine kinase levels are characteristic of PMR, while elevated creatine kinase levels may be seen in other conditions such as post-infection myositis 2, 3, 5
• Muscle biopsy and electromyography may be useful in diagnosing specific muscle abnormalities, such as muscle vasculitis or inflammatory myopathy 2, 3, 4