What is the evaluation and treatment approach for dermatomyositis (DM)?

Evaluation and Management of Dermatomyositis

Initial Diagnostic Workup

All patients with suspected dermatomyositis require a comprehensive laboratory, imaging, and functional assessment to confirm diagnosis, assess disease severity, and screen for associated malignancy. 1

Essential Laboratory Testing

• Muscle enzymes including creatine phosphokinase (CPK), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and aldolase must be measured, recognizing that these may be normal despite active disease 2, 1
• Myositis-specific autoantibodies (anti-TIF1-γ, anti-NXP2, anti-MDA5, anti-SRP) should be measured when available for prognostic information and to identify disease subsets 2, 1
• Complete blood count, inflammatory markers (ESR, CRP), renal and liver function tests are required 2, 1
• Troponin to evaluate myocardial involvement 2
• Consider myositis-associated antibodies (anti-PmScl, anti-U1-RNP, anti-La, anti-Ro, anti-Sm) in patients with overlap features 2

Muscle Assessment

• Formal muscle strength testing using validated tools such as Manual Muscle Test (MMT8) and Childhood Myositis Assessment Scale (CMAS) at diagnosis and all follow-up visits 2, 1
• MRI with T2-weighted/STIR sequences is the preferred imaging modality for detecting muscle inflammation and monitoring disease activity, and must be interpreted by an expert radiologist 2, 1, 3
• Muscle biopsy should be performed in all cases where presentation is atypical, particularly in the absence of characteristic rash or skin signs, using standardized scoring tools 2
• Electromyography (EMG) should be considered to differentiate myopathy from neuropathy when diagnosis is uncertain, though it does not reliably detect metabolic myopathies 2
• Muscle ultrasonography may show increased echo intensity when performed by an experienced sonographer if MRI or biopsy is not possible 2

Skin Assessment

• Nailfold capillaroscopy should be performed at diagnosis and disease flares, with regular follow-up assessments 2, 1
• Formal Cutaneous Assessment Tool (CAT) should be used for diagnosis and monitoring skin disease activity over time; alternative tools include DAS (skin) or MITAX (skin) 2, 1
• Look for pathognomonic findings: heliotrope rash, Gottron's papules, Gottron's sign, V-sign, shawl sign 4
• Assess for periungual telangiectasias, cuticular overgrowth, "mechanic's hands," palmar papules, poikiloderma, and calcinosis 4

Organ-Specific Evaluations

Cardiac:

• Echocardiography and ECG are required at diagnosis for all patients 2, 1
• Repeated cardiac evaluation is needed for high-risk patients (hypertension, high disease activity 1 year post-diagnosis, long-term high corticosteroid burden, chronic ongoing active disease) 2

Pulmonary:

• Pulmonary function tests including CO diffusion capacity should be performed at diagnosis 2, 1
• If pulmonary function tests indicate interstitial lung disease, obtain chest X-ray and/or high-resolution CT 2

Gastrointestinal:

• Swallow function must be formally assessed in every patient using speech and language therapy evaluation, video fluoroscopy, or barium studies 2, 1

Calcinosis:

• Plain radiographs may be used for evaluation of calcinosis, which should be looked for in all patients 2

Malignancy Screening

• All adult patients with dermatomyositis require screening for associated malignancy at diagnosis, as they have a three to eight times increased risk compared to the general population 4
• Screening should include age-appropriate cancer screening and consideration of CT chest/abdomen/pelvis 5, 4

Treatment Approach

Initial Therapy

High-dose corticosteroids (oral or intravenous) combined with methotrexate is the recommended induction regimen for newly diagnosed dermatomyositis, representing Level 1B evidence with 100% expert consensus. 1

Skin-Specific Management

• Sun protection with routine sunblock on all sun-exposed areas is essential 1, 5
• Topical corticosteroids for localized skin lesions 5
• Antimalarials (hydroxychloroquine) for cutaneous disease 5
• Methotrexate and/or intravenous immunoglobulin for refractory skin disease 5

Multidisciplinary Care

• Physiotherapist and specialist nurse involvement is recommended 1
• Speech and language therapy for dysphagia 2

Monitoring Strategy

• Disease activity should be assessed regularly using standardized tools such as the Disease Activity Score 1
• Disease damage should be assessed at least yearly using the Myositis Damage Index 1
• Muscle enzymes (CK), inflammatory markers (ESR, CRP), and muscle strength should be monitored at each visit 2, 1
• Patient-reported outcome measures such as the Health Assessment Questionnaire and visual analogue scales are helpful for assessing disease activity 1
• Serial MRI can be used to monitor disease activity and treatment response 1, 3

Common Pitfalls

• Do not exclude dermatomyositis based on normal muscle enzymes alone, as they may be normal despite active disease 2, 1
• Do not delay malignancy screening in adult patients, as the association is significant and early detection improves outcomes 4
• Do not overlook cardiac and pulmonary involvement, as these can significantly impact morbidity and mortality 2
• Recognize that clinically amyopathic dermatomyositis (classic cutaneous manifestations for >6 months without muscle weakness or enzyme elevation) still requires full systemic evaluation including pulmonary assessment 4

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