Overview
Definition:
Juvenile dermatomyositis (JDM) is a rare, idiopathic inflammatory myopathy characterized by inflammation of the muscles (myositis) and skin (dermatomyositis), primarily affecting children
It is considered an autoimmune disease where the body's immune system mistakenly attacks its own tissues.
Epidemiology:
JDM is the most common idiopathic inflammatory myopathy of childhood
Its incidence is estimated at 2-4 cases per million children per year
It affects females more commonly than males, with a female-to-male ratio of approximately 2:1
Onset typically occurs between ages 5 and 14 years.
Clinical Significance:
JDM poses significant challenges in diagnosis and management due to its variable presentation and potential for long-term sequelae, including muscle damage, contractures, calcinosis, and growth retardation
Early diagnosis and aggressive treatment are crucial to prevent irreversible disability and improve quality of life for affected children
Understanding its pathogenesis and therapeutic strategies is vital for pediatricians and pediatric rheumatologists.
Clinical Presentation
Symptoms:
Insidious onset of proximal muscle weakness
Difficulty climbing stairs, rising from a chair, or lifting arms
Facial muscle weakness leading to dysphagia or dysarthria
Fatigue and lethargy
Low-grade fever
Abdominal pain
Arthralgias
Raynaud's phenomenon may be present
Children may complain of "growing pains" or reluctance to play.
Signs:
Heliotrope rash: violaceous discoloration of the eyelids, often with edema
Gottron's papules/pustules: erythematous to violaceous papules or plaques over the extensor surfaces of the knuckles, elbows, and knees
Gottron's sign: erythema over the dorsal aspects of the joints
Shawl sign: erythematous rash over the shoulders and upper chest
V sign: rash over the anterior chest
Periungual erythema and telangiectasias
Scalp scaling
Muscle tenderness and weakness on examination
Palpable subcutaneous nodules (calcinosis) may develop later.
Diagnostic Criteria:
The Bohan and Peter criteria for dermatomyositis are often adapted for JDM
Diagnosis typically requires the presence of: characteristic skin rash AND evidence of muscle involvement (progressive, symmetric proximal muscle weakness, elevated muscle enzymes, characteristic EMG findings, inflammatory myopathy on muscle biopsy)
Additional support comes from positive autoantibodies, especially anti-Jo-1, anti-Mi-2, and anti-TIF1-gamma.
Diagnostic Approach
History Taking:
Detailed history of the onset and progression of muscle weakness, focusing on daily activities
Inquire about difficulty with motor milestones in younger children
Assess for associated symptoms like fever, joint pain, abdominal pain, or dysphagia
Ask about any skin changes
Family history of autoimmune diseases
Medication history.
Physical Examination:
Careful examination of the skin for heliotrope rash, Gottron's papules, and other characteristic rashes
Assess muscle strength systematically using grading scales (e.g., MRC scale) focusing on proximal muscle groups
Examine for joint swelling or tenderness
Assess for any signs of cardiopulmonary involvement
Palpate for subcutaneous nodules
Evaluate for any signs of dysphagia or dysarthria.
Investigations:
Laboratory tests: Complete blood count (CBC) with differential, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) to assess inflammation
Muscle enzymes: creatine kinase (CK), aldolase, lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT)
CK is the most specific marker of muscle damage
Autoantibodies: Anti-nuclear antibody (ANA) is positive in most JDM patients
Specific myositis-associated antibodies like anti-Mi-2, anti-Jo-1 (histidyl-tRNA synthetase), anti-PL-7, anti-PL-12, anti-EJ, anti-OJ, anti-SRP, and anti-TIF1-gamma are important for diagnosis and prognosis
Electromyography (EMG): can reveal myopathic changes (short, small-amplitude, polyphasic motor unit potentials) and irritative myopathy
Muscle biopsy: considered the gold standard, showing perifascicular atrophy, perifascicular inflammation, muscle fiber necrosis, and regeneration
However, it is invasive and may not be representative if inflammation is patchy
MRI: can identify active muscle inflammation and edema, guiding biopsy location if needed
Echocardiography: to rule out pericardial effusion
Pulmonary function tests (PFTs): if pulmonary involvement is suspected.
Differential Diagnosis:
Other inflammatory myopathies (adult dermatomyositis, polymyositis), other connective tissue diseases (lupus, scleroderma), muscular dystrophies, metabolic myopathies, infections (viral myositis), endocrine myopathies, and juvenile idiopathic arthritis (JIA) with myalgia
Distinguishing JDM often relies on the presence of the characteristic cutaneous manifestations.
Management
Initial Management:
Prompt initiation of immunosuppressive therapy is crucial to control inflammation and prevent long-term damage
Corticosteroids are the cornerstone of treatment
Monitoring of muscle strength, inflammatory markers, and organ systems is essential.
Medical Management:
Corticosteroids: Oral prednisone is the first-line treatment, typically initiated at 1-2 mg/kg/day (maximum 60 mg/day) in divided doses or as a single morning dose
Intravenous methylprednisolone pulses (e.g., 30 mg/kg once a month for 6 months) may be used for severe disease
Steroid-sparing agents are introduced to allow for gradual steroid tapering and to improve long-term outcomes
These include methotrexate (MTX), which is often the second-line agent (10-20 mg/m²/week), or intravenous immunoglobulin (IVIG), particularly in patients with severe muscle weakness, dysphagia, or significant skin involvement
Other agents like azathioprine, mycophenolate mofetil, tacrolimus, or rituximab may be used in refractory cases.
Surgical Management:
Surgical management is generally not indicated for the primary inflammatory process
However, surgical intervention may be required for complications like contractures, carpal tunnel syndrome, or removal of problematic calcinosis deposits, although removal of calcinosis is often avoided due to risk of infection and recurrence.
Supportive Care:
Physical and occupational therapy: Essential for maintaining muscle strength, range of motion, and functional independence
They help prevent contractures and improve motor skills
Nutritional support: Adequate caloric and protein intake is important for muscle repair and growth
Sun protection: Due to photosensitivity associated with JDM rashes, rigorous sun protection with high SPF sunscreen and protective clothing is vital
Calcium and Vitamin D supplementation may be beneficial, especially during long-term steroid therapy to prevent osteoporosis
Monitoring for and managing calcinosis, which can impair joint function and mobility
Regular ophthalmological and audiological evaluations.
Complications
Early Complications:
Severe muscle weakness leading to inability to ambulate or perform daily activities
Dysphagia and aspiration pneumonia
Respiratory muscle weakness
Vasculitis affecting gastrointestinal tract (rare)
Acute kidney injury.
Late Complications:
Calcinosis: deposition of calcium in subcutaneous tissues, muscles, and tendons, causing pain, restricted movement, and skin ulcerations
Muscle atrophy and fibrosis
Joint contractures
Osteoporosis from long-term corticosteroid use
Growth retardation
Skin hyperpigmentation or hypopigmentation
Residual muscle weakness.
Prevention Strategies:
Aggressive and timely immunosuppressive therapy to prevent muscle damage
Physical and occupational therapy to maintain function and prevent contractures
Judicious use of corticosteroids and consideration of steroid-sparing agents to minimize long-term side effects
Adequate calcium and vitamin D supplementation
Strict sun protection to prevent exacerbation of skin lesions
Monitoring for calcinosis and prompt management if symptomatic.
Prognosis
Factors Affecting Prognosis:
Early diagnosis and treatment
Response to initial therapy
Presence of specific autoantibodies (e.g., anti-Mi-2 antibodies are often associated with a better prognosis)
Severity of muscle and skin involvement
Development of calcinosis
Extramuscular manifestations.
Outcomes:
With appropriate treatment, the prognosis for JDM is generally good, with most children achieving remission or significant improvement
Approximately 70-80% of patients achieve clinical remission within 2-5 years
However, some children may experience chronic or relapsing disease, and long-term sequelae like calcinosis and residual muscle weakness can persist
Untreated or poorly controlled JDM can lead to significant disability.
Follow Up:
Long-term follow-up is essential, typically with a pediatric rheumatologist, to monitor for disease activity, treatment efficacy, and potential long-term complications
This includes regular clinical assessments of muscle strength, skin status, and organ systems, as well as monitoring of laboratory parameters (muscle enzymes, inflammatory markers)
Gradual tapering of immunosuppressive medications can be attempted once sustained remission is achieved, but relapses can occur, necessitating reinitiation or adjustment of therapy.
Key Points
Exam Focus:
JDM is characterized by symmetric proximal muscle weakness and pathognomonic skin rashes (heliotrope rash, Gottron's papules)
Key investigations include elevated muscle enzymes (CK), positive ANA, and specific myositis autoantibodies (anti-Mi-2, anti-Jo-1)
First-line treatment is high-dose corticosteroids, with methotrexate as a common steroid-sparing agent
Calcinosis is a significant long-term complication.
Clinical Pearls:
Always consider JDM in a child presenting with new onset weakness and a characteristic rash
Differentiate from other causes of childhood weakness and rash
Aggressive treatment is crucial to prevent irreversible muscle damage and disability
Monitor for drug toxicity and long-term complications like calcinosis and osteoporosis
Multidisciplinary care involving rheumatology, physical therapy, and dermatology is vital.
Common Mistakes:
Delaying diagnosis by attributing weakness to "growing pains" or behavioral issues
Underestimating the severity of muscle weakness or potential for respiratory compromise
Insufficient immunosuppressive therapy or premature tapering of steroids
Neglecting sun protection leading to worsening of skin lesions
Underestimating the impact of calcinosis on function and mobility.