What is the initial workout regimen for a patient with dermatomyositis?

Initial Workup for Dermatomyositis

The initial workup for dermatomyositis requires a comprehensive rheumatologic and neurologic history with focused examination of muscle strength, skin findings, blood testing for muscle inflammation markers (CK, aldolase, AST, ALT, LDH), cardiac evaluation with troponin and ECG, autoantibody testing, and inflammatory markers (ESR, CRP). 1

Clinical History and Physical Examination

Key Historical Elements

• Complete rheumatologic and neurologic history focusing on the pattern and progression of muscle weakness, which is more typical than pain in myositis 1
• Skin examination for characteristic dermatomyositis findings including heliotrope rash, Gottron's papules, and other cutaneous manifestations 1
• Assessment of pre-existing conditions that could cause similar symptoms to establish differential diagnosis 1

Physical Examination Components

• Manual muscle testing (MMT) of bilateral muscle groups: neck flexion/extension, shoulder abduction, elbow flexion/extension, wrist flexion/extension, hip flexion/extension, hip abduction/adduction, knee flexion/extension, ankle dorsiflexion, and plantar flexion 1
• Muscle strength grading using the UK Medical Research Council System scale (0-5), where 0 indicates lowest strength and 5 the highest 1
• Complete neurologic examination to evaluate for overlap with neurologic syndromes such as myasthenia gravis 1

Laboratory Workup

Essential Blood Tests

• Muscle enzyme panel: Creatine kinase (CK), aldolase, aspartate aminotransferase (AST), alanine transaminase (ALT), and lactate dehydrogenase (LDH) 1
• Inflammatory markers: Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) 1
• Troponin to evaluate for myocardial involvement 1

Autoantibody Testing

• Myositis-specific autoantibodies: Anti-TIF1γ, anti-NXP2, and other myositis autoantibodies as indicated, particularly if muscle-related manifestations preceded any potential immune checkpoint inhibitor therapy 1
• Myasthenia gravis antibodies: Anti-acetylcholine receptor (anti-AChR) and antistriational antibodies to evaluate possible concomitant myasthenia gravis 1

Additional Testing

• Urinalysis for rhabdomyolysis 1

Cardiac Evaluation

Cardiac assessment is critical given the risk of myocardial involvement in dermatomyositis:

• Electrocardiogram (ECG) 1
• Echocardiogram or cardiac MRI should be considered based on troponin results and clinical suspicion 1

Advanced Diagnostic Studies (When Indicated)

Consider on Individual Basis

• Electromyography (EMG) when diagnosis is uncertain 1
• MRI imaging of affected muscle groups when diagnosis is uncertain or to guide biopsy 1
• Muscle biopsy when diagnosis is uncertain and overlap with neurologic syndromes is suspected 1

Important caveat: Muscle enzyme levels and muscle strength testing may not always accurately reflect disease activity, especially if muscle tissue is affected by chronic atrophy 1

Functional Assessment Tools

Core Set Measures

The International Myositis Assessment and Clinical Studies (IMACS) group has established validated core set measures 1:

• Physician Global Activity on 10-cm Visual Analogue Scale (VAS) 1
• Patient Global Activity on 10-cm VAS 1
• Manual Muscle Testing (MMT) - can use full 26 muscle groups or shortened MMT8 (8 proximal, distal, and axial muscle groups on one side) 1
• Health Assessment Questionnaire (HAQ) - self-survey assessing activities of daily living with score range 0-3.0 (0.1-1.0 = mild disability; 1.01-2.0 = moderate disability; 2.01-3.0 = severe disability) 1
• Extramuscular Global Activity measured by physician on 10-cm VAS 1
• Most abnormal serum muscle enzyme 1

Common Pitfalls to Avoid

• Do not rely solely on muscle enzymes: CK can be normal in active dermatomyositis, particularly when skin disease predominates 1
• Do not overlook cardiac involvement: Myocardial involvement can be life-threatening and requires specific evaluation 1
• Do not confuse with viral myositis: Viral myositis presents with benign, self-limited course, bilateral lower extremity involvement, preserved strength, absence of rash, and normal or only mildly elevated CPK 2
• Do not delay physical therapy: Physical therapy should be instituted early to avoid joint contractures and muscle atrophy from disuse 1