What are the clinical features of dermatomyositis?

Clinical Features of Dermatomyositis

Dermatomyositis presents with characteristic pathognomonic skin findings combined with symmetric proximal muscle weakness, though skin manifestations may precede muscle involvement by months to years. 1

Cutaneous Manifestations

The skin findings are often the most distinctive features and may appear before muscle symptoms:

• Heliotrope rash: Violaceous periorbital edema with erythema, particularly prominent in anti-Mi-2 positive patients 1, 2
• Gottron's papules: Erythematous to violaceous papules over the extensor surfaces of the metacarpophalangeal and interphalangeal joints 1, 2
• Gottron's sign: Erythematous macules over bony prominences including elbows and knees 2
• V-sign: Erythema over the anterior chest, frequently observed in anti-Mi-2 positive disease 1
• Shawl sign: Erythema distributed over the shoulders and upper back 3
• Periungual changes: Nailfold telangiectasias and splinter hemorrhages, with nailfold capillaroscopy being particularly useful for predicting disease severity 4, 2
• Mechanic's hands: Hyperkeratotic, cracked skin on the palms and fingers, associated with antisynthetase syndrome 1
• Photosensitivity: UV light exposure may trigger disease onset, particularly in anti-Mi-2 positive patients 1

Important caveat: Poikiloderma (mottled hyperpigmentation, hypopigmentation with telangiectasias) can develop and may initially present as erythroderma in rare cases, though this typically responds well to treatment 3

Muscular Manifestations

The muscle involvement follows a characteristic pattern that impacts daily function:

• Symmetric proximal muscle weakness: Difficulty rising from a chair, climbing stairs, lifting objects overhead, and combing hair 1
• Progressive onset: Weakness typically develops over weeks to months 1
• Preserved distal strength: Unlike inclusion body myositis, distal muscles are typically spared 4
• Muscle pain: May accompany weakness but is not always present 2

Extramuscular Manifestations

These systemic features significantly impact morbidity and mortality:

Pulmonary Involvement

• Interstitial lung disease: Common, particularly in patients with antisynthetase syndrome (anti-Jo-1, anti-PL-7, anti-PL-12) and anti-MDA5 antibodies 1
• Aspiration pneumonia: Secondary to dysphagia and cricopharyngeal dysfunction 4

Gastrointestinal Involvement

• Dysphagia: Prominent feature due to cricopharyngeal muscle dysfunction and esophageal dysmotility 4, 1
• Vasculopathy: In juvenile dermatomyositis, can lead to bowel ischemia and infarction 4

Cardiac Involvement

• Arrhythmias: Including asymptomatic sinus tachycardia detected on electrocardiography 4, 1
• Conduction abnormalities: May occur without overt symptoms 1
• Diastolic dysfunction: Visible on echocardiography 4, 1
• Myocarditis: Although not typical, may be found on autopsy studies 4

Critical pitfall: Cardiac manifestations are often asymptomatic, requiring proactive screening with ECG and echocardiography, particularly in anti-SRP positive patients 1

Other Systemic Features

• Raynaud phenomenon: Particularly in antisynthetase syndrome 4, 1
• Inflammatory arthritis: Non-erosive polyarthritis may occur 4
• Calcinosis cutis: More common in juvenile dermatomyositis 4

Laboratory Findings

Objective markers support the clinical diagnosis:

• Elevated muscle enzymes: Creatine kinase (CK), aldolase, LDH, AST, and ALT are typically elevated 1, 5
• Myositis-specific antibodies: Anti-Jo-1 (most common antisynthetase antibody at ~20%), anti-Mi-2 (<10%), anti-TIF1-γ (associated with malignancy in adults), anti-MDA5 (associated with rapidly progressive ILD), anti-SRP (necrotizing myopathy with cardiomyopathy) 1, 5
• Abnormal EMG: Short-duration, low-amplitude, polyphasic motor unit potentials with increased spontaneous activity 1

Diagnostic Criteria

The Bohan and Peter criteria remain widely used, requiring 4 of 5 features for definite diagnosis:

1. Characteristic skin findings
2. Proximal muscle weakness
3. Elevated muscle enzyme levels
4. Myopathic pattern on EMG
5. Evidence of endomysial, mononuclear inflammatory infiltrate on muscle biopsy 4

Clinical Variants

Amyopathic Dermatomyositis

• Classic DM rash without muscle weakness 4
• Normal muscle enzyme levels within 2 years of diagnosis and normal EMG 4
• Interstitial lung disease may still occur 4
• Lower but still present malignancy risk compared to classic DM 4

Critical warning: Do not dismiss patients with classic skin findings but no muscle weakness—they require the same malignancy screening and monitoring for ILD as classic DM 5

Hypomyopathic Dermatomyositis

• No muscle weakness but evidence of subclinical muscle inflammation 4
• Mild CK elevation, EMG abnormalities, or MRI evidence of muscle inflammation 4

Juvenile Dermatomyositis

• Presents in patients <18 years with similar skin and muscle features to adult DM 4
• Higher incidence of calcinosis cutis, vasculopathy, and dysphonia 4
• Nailfold capillaroscopy particularly useful for predicting severity and monitoring disease course 4

Malignancy Association

Adult-onset dermatomyositis carries a 20% risk of associated malignancy, requiring comprehensive cancer screening at diagnosis and during follow-up. 5

• Highest risk: Anti-TIF1-γ (anti-p155/140) positive patients in adults 1, 5
• Timing: Malignancy may precede, coincide with, or follow DM diagnosis 6
• Lower risk: Anti-Mi-2 positive patients and juvenile dermatomyositis 1