What is the diagnostic workup for dermatomyositis (inflammatory myopathy)?

From the Guidelines

A dermatomyositis workup involves a comprehensive evaluation including a thorough history and physical examination, laboratory tests such as muscle enzymes and autoantibody testing, and imaging studies like MRI to diagnose this inflammatory muscle disease characterized by skin rash and muscle weakness. The workup begins with a thorough history and physical examination, focusing on muscle strength assessment and identification of characteristic skin findings like Gottron's papules and heliotrope rash, as recommended by the most recent guidelines 1. Key components of the workup include:

• Laboratory tests to evaluate muscle inflammation, such as CK, aldolase, AST, ALT, and LDH, as well as inflammatory markers like ESR and CRP 1.
• Autoantibody testing to evaluate possible concomitant myasthenia gravis and other specific autoantibodies associated with dermatomyositis, such as anti-TIF1-γ, anti-NXP2, and other myositis autoantibodies 1.
• Electromyography (EMG) to identify myopathic changes, and muscle biopsy to provide definitive diagnosis by showing perifascicular atrophy and inflammatory infiltrates, considered on an individual basis when diagnosis is uncertain 1.
• Imaging studies like MRI to detect muscle inflammation and guide biopsy sites, and to evaluate for cardiac involvement with tests such as troponin, ECG, and echocardiogram or cardiac MRI 1. Given the association of dermatomyositis with underlying malignancy in adults, age-appropriate cancer screening is essential, including chest/abdomen/pelvis CT scans, mammography, colonoscopy, and gynecological examination, as part of a comprehensive approach to ensure accurate diagnosis and identify potential complications or associated conditions requiring treatment 1.

From the Research

Dermatomyositis Workup

A dermatomyositis workup typically involves a combination of clinical evaluation, laboratory tests, and imaging studies to diagnose and manage the condition. The key components of a dermatomyositis workup include:

• Clinical evaluation: A thorough medical history and physical examination to assess muscle weakness, skin lesions, and other systemic symptoms 2, 3, 4
• Laboratory tests:
  • Elevated creatine kinase (CK) levels: A common marker of muscle damage 2, 5
  • Elevated aldolase levels: May be present in some cases of dermatomyositis, even with normal CK levels 5
  • Electromyography (EMG): To assess muscle function and detect abnormalities 2
  • Muscle biopsy: To confirm the diagnosis and assess the extent of muscle damage 2
• Imaging studies:
  • Pulmonary function tests: To evaluate for interstitial lung disease, which is present in approximately 30% of patients with dermatomyositis 2, 6
  • Other imaging studies (e.g., chest X-ray, CT scan): To evaluate for malignancy or other systemic involvement 2, 6

Diagnostic Criteria

The diagnosis of dermatomyositis is based on a combination of clinical, laboratory, and histopathological findings. The presence of myositis-specific antibodies (MSAs) can also be helpful in diagnosing and managing the condition 3, 4, 6. The diagnostic criteria for dermatomyositis include:

• Symmetrical proximal muscle weakness
• Characteristic skin lesions (e.g., heliotrope rash, Gottron's papules)
• Elevated CK or aldolase levels
• Abnormal EMG or muscle biopsy findings
• Presence of MSAs (e.g., anti-Mi2, anti-MDA5, anti-NXP2) 4

Malignancy and Interstitial Lung Disease Screening

Patients with dermatomyositis are at increased risk of developing malignancy and interstitial lung disease. Therefore, screening for these conditions is an essential part of the workup 2, 6. The screening tests may include:

• Malignancy screening: Age-appropriate cancer screening tests (e.g., mammography, colonoscopy) 2, 6
• Interstitial lung disease screening: Pulmonary function tests, chest X-ray, or CT scan 2, 6