Signs of Dermatomyositis
Dermatomyositis presents with characteristic cutaneous findings combined with symmetric proximal muscle weakness, though skin manifestations may appear alone or precede muscle involvement by months to years. 1
Pathognomonic Cutaneous Signs
The following skin findings are diagnostic of dermatomyositis:
- Heliotrope rash: Violaceous periorbital edema with erythema 1
- Gottron papules: Erythematous to violaceous papules over the dorsal metacarpophalangeal and interphalangeal joints 1, 2
- Gottron sign: Erythematous macules over bony prominences (elbows, knees) 2
Characteristic Cutaneous Manifestations
Additional skin findings strongly associated with dermatomyositis include:
- Periungual telangiectasias with cuticular overgrowth 1, 2
- Poikiloderma: Atrophic skin changes with hyperpigmentation, hypopigmentation, and telangiectasias 1
- Photosensitive erythematous rash involving face, neck, torso, and extensor surfaces of extremities 1
- V-sign and shawl sign: Erythema over anterior chest/neck and upper back/shoulders 2
- "Mechanic's hands": Hyperkeratotic, cracked skin on palmar and lateral aspects of fingers 2
Musculoskeletal Signs
The muscle involvement follows a characteristic pattern:
- Symmetric proximal muscle weakness developing over weeks to months 1
- Difficulty with tasks requiring proximal strength (climbing stairs, rising from chairs, lifting arms overhead) 1
- Elevated muscle enzyme levels (creatine kinase, aldolase, AST, ALT, LDH) 1
- Muscle tenderness may be present but is not universal 1
Extramuscular Manifestations
Systemic involvement significantly impacts morbidity and mortality:
Pulmonary
- Interstitial lung disease (most common pulmonary manifestation, presenting as nonspecific interstitial pneumonitis) 1, 3
- Aspiration pneumonia secondary to pharyngeal muscle weakness 1
Gastrointestinal
Cardiac
- Asymptomatic arrhythmias (sinus tachycardia) detected on electrocardiography 1
- Diastolic dysfunction on echocardiography 1
- Myocarditis (found on autopsy studies, associated with increased mortality) 1, 3
Constitutional
Diagnostic Criteria (Bohan and Peter)
A definite diagnosis requires 4 of 5 criteria:
- Characteristic skin findings 1
- Proximal muscle weakness 1
- Elevated muscle enzyme levels 1
- Myopathic pattern on EMG (polyphasic motor unit action potentials of short duration and low amplitude, increased insertional activity with fibrillation potentials) 1
- Endomysial mononuclear inflammatory infiltrate on muscle biopsy 1
Special Variants
Amyopathic Dermatomyositis
- Classic rash without muscle weakness 1
- Normal muscle enzyme levels within 2 years of diagnosis 1
- Normal EMG findings 1
- Interstitial lung disease may still occur 1
Hypomyopathic Dermatomyositis
- Classic rash without clinical muscle weakness 1
- Evidence of subclinical muscle inflammation (mild CK elevation, EMG abnormalities, MRI changes) 1
Juvenile Dermatomyositis
- Occurs in patients <18 years of age 1
- Calcinosis cutis is characteristic (less common in adults) 1, 3
- Cutaneous vasculitis and ulcerations more frequent than in adults 1
- Gastrointestinal vasculopathy with potential bowel ischemia/infarction 1
- Nailfold capillaroscopy useful for predicting disease severity 1
Critical Clinical Pitfalls
Screen all newly diagnosed patients for malignancy, as dermatomyositis carries a 3-8 times increased cancer risk compared to the general population 2. This risk is particularly elevated in elderly patients 3.
Cardiac involvement and dysphagia are poor prognostic factors that significantly increase morbidity and mortality 3. Even asymptomatic cardiac manifestations warrant monitoring, as severe complications may not be clinically apparent initially 1.
Myositis-specific autoantibodies predict extramuscular organ involvement (particularly pulmonary and cardiac systems) and offer prognostic value 1, 3. Testing should be performed at diagnosis to guide monitoring strategies.