What is Dermatomyositis?
Dermatomyositis is a rare autoimmune inflammatory myopathy characterized by pathognomonic skin manifestations and proximal muscle weakness, with significant systemic involvement affecting multiple organ systems, particularly the lungs and heart. 1
Core Disease Characteristics
Dermatomyositis is one of the main representatives of idiopathic inflammatory myopathies (IIMs), a heterogeneous group of autoimmune disorders with varying organ manifestations, prognoses, and therapeutic responses. 2 The disease affects both children and adults, with two peaks of incidence: childhood between 5-15 years and adulthood between 40-60 years, showing female preponderance. 3
- The incidence is approximately 9.63 per 1,000 people. 4
- All idiopathic inflammatory myopathies are systemic diseases with significant extramuscular involvement. 1
Pathognomonic Clinical Features
Skin Manifestations
The characteristic cutaneous findings include heliotrope rash (violaceous periorbital edema), Gottron papules (erythematous papules over the extensor surfaces of joints), periungual telangiectasias, and poikiloderma. 1
- Additional skin findings include Shawl sign, mechanic's hands, and livedo reticularis. 4, 5
- Skin disease tends to be chronic, negatively impacts quality of life, and is often more recalcitrant to therapy than muscle involvement. 6
Muscle Involvement
Proximal muscle weakness is the hallmark muscular manifestation, though amyopathic dermatomyositis exists where skin lesions occur without clinically evident muscle weakness. 3
- Elevated muscle enzymes (creatine phosphokinase, aldolase) typically accompany muscle involvement. 4, 5
- Constitutional symptoms including fever, weight loss, and fatigue occur across all inflammatory myopathies. 1
Critical Systemic Complications
Pulmonary Disease
Interstitial lung disease (ILD) is the most common pulmonary manifestation and represents a major cause of morbidity and mortality in dermatomyositis patients. 1
- ILD is present in approximately 8% of patients and can be asymptomatic. 7
- ILD prevalence in idiopathic inflammatory myopathies averages 30%, varying from 6% in juvenile dermatomyositis to 71% in antisynthetase syndrome. 2
- ILD typically presents as nonspecific interstitial pneumonitis. 1
- In 13-38% of patients, ILD can be the first manifestation and precede the diagnosis of autoimmune disease by several years. 2
Cardiac Involvement
Cardiac system involvement includes pericarditis, myocarditis, systolic and diastolic dysfunction, and arrhythmias, and is associated with poorer outcomes and increased mortality. 1, 7
- Overlooking cardiac involvement can be potentially life-threatening. 7
Gastrointestinal Manifestations
Dysphagia is a common complication and represents a poor prognostic factor. 1
- Gastrointestinal vasculopathy can occur, particularly in juvenile dermatomyositis. 1
Calcinosis
Calcinosis cutis is characteristic of juvenile dermatomyositis, occurring less frequently in adults, developing on average 2.9 years after disease onset and causing pain and functional impairment. 1, 7
Pathogenesis and Autoantibodies
Recent studies have highlighted the activation of the innate immune system, including high expression of interferons (IFNs) and IFN-regulated proteins, as an important pathological hallmark of dermatomyositis. 5
- Inappropriate activation of the innate immune system with secondary dysregulation of the adaptive immune response is now considered a central pathogenetic feature. 5
- Myositis-specific autoantibodies predict specific extramuscular organ involvement, particularly pulmonary and cardiac systems, and offer prognostic value. 1
- High-risk autoantibodies include Jo-1 and MDA-5, which are associated with increased ILD risk. 2
Malignancy Association
Dermatomyositis has been associated with malignancy, with elderly patients having particularly high malignancy risk. 1, 8
- Every newly diagnosed patient should undergo screening investigations for malignancy. 3
- Certain autoantibodies are associated with cancer risk. 3
Poor Prognostic Indicators
Poor prognostic indicators that increase morbidity and mortality include advanced age at presentation, presence of dysphagia, cardiac involvement, associated malignancy, and severe interstitial lung disease. 1
Diagnostic Approach
The American College of Rheumatology recommends laboratory testing including muscle enzymes and inflammatory markers for diagnosis. 7
- Pulmonary evaluation with pulmonary function tests is essential for diagnosing interstitial lung disease. 7
- Imaging studies such as high-resolution CT and MRI are helpful in diagnosing and monitoring complications. 7
- Muscle biopsy helps in diagnosis, though findings may be nonspecific, showing myofiber atrophy with perivascular and endomysial T-lymphocytes and histiocytes. 4
Screening Recommendations for High-Risk Patients
Baseline pulmonary function tests and high-resolution CT are recommended in all patients, with yearly pulmonary function tests for high-risk patients (those with Jo-1 or MDA-5 antibodies). 2
- Regular disease activity assessment using validated tools is essential. 7
- Yearly evaluation of damage using standardized measures such as the Myositis Damage Index is recommended. 7
- Cardiac monitoring with repeated cardiac evaluation is necessary for high-risk patients. 7