General Information
It is a multisystemic disease characterized by inflammation of striated muscles (proximal skeletal muscles, heart, respiratory muscles and esophagus) and skin.
epidemiology
• It is the most common cause of pediatric inflammatory myopathy.
• Average age of onset; 4-10 years old.
• Girl/boy: 2/1
• Associated with HLA B8, DRB1 and DQA1.
Clinic:
• Rash is the first finding in half of the cases.
• The characteristic skin lesion is a heliotropic rash (blue-purple color on the eyelids). There is also a typical scarf or shawl rash and facial erythema around the chest and neck.
• Classic Gottron's papules are bright pink or pale, thick or atrophic plaques mostly seen in the proximal and distal interphalangeal joints.
• A thick, erythematous and peeling rash on the palms and soles (mechanic's hand) was associated with anti-Jo-1 antibodies.
• The first place where vasculitis occurs is the nail bed. With nail base capillaroscopy, pitting at the nail base and periungual telangiectasias can be demonstrated even with the naked eye.
• Muscle weakness symmetrically involves the proximal muscles (neck flexors, shoulder junction and hip flexors). They have difficulty getting out of bed, climbing stairs, and combing hair. Gowers sign is detected.
• Esophageal muscles (dysphagia, difficulty swallowing and aspiration, gastroesophageal reflux) and respiratory muscles (respiratory failure) may be involved.
• Lipodystrophy and calcinosis (30-40%) are seen in long-term and poorly treated disease. While lipodystrophy causes loss of fat tissue in the face and upper body; calcinosis occurs in subcutaneous tissue and muscle.
• Abdominal pain and occult blood in the stool are signs of gastrointestinal vasculitis. May cause perforation.
• Rarely, pericarditis, myocarditis and arrhythmias may be encountered.
Diagnostic Criteria:
Diagnosis is made when three of the following are positive in addition to the cutaneous manifestations of heliotropic rash (characteristic) or Gottron's papules.
1. Symmetrical proximal muscle weakness {Gowers' syndrome (+))
2. Elevated muscle enzymes (CPK, LDH, AST, Aldolase)
3. Abnormal EMG (myopathy and denervation)
4. Inflammation on muscle biopsy, vasculitis or necrosis .
1. The most common finding is muscle weakness.
2. The most common enzyme elevation at the time of diagnosis is ALT (high even when CPK is normal)
3. Pm/Scl may be positive in patients with pulmonary interstitial fibrosis and cardiac involvement in long-term disease.
4. Myositis-specific antibodies such as anti Jo-1, anti Mi-2, anti-p155/140, anti-NXP2 are associated with complications.
5. Lipodystrophy develops in 10-40% of cases; It is associated with insulin resistance, acanthosis nigrigans, dyslipidemia, hypertension and menstrual irregularity.
Laboratory Findings:
• Muscle enzymes increased (CPK, LDH, AST, aldolase)
• ANA (+) is seen in >80% of cases, but other antibodies (Anti-Ro-La, Anti-Sm and Antids DNA) are negative.
• The sedimentation rate is usually normal.
• Rheumatoid factor (RF) is negative.
• Anti Jo antibodies are {+) {An important indicator for Lung involvement in JDM is antibodies against t-RNA synthetase).
Treatment:
• All children should be protected from sunlight and UV protection cream should be used.
• Adequate vitamin D and calcium supplementation should be given (to prevent steroid-induced osteopenia).
• Steroid (first choice)
• Methotrexate or hydroxychloroquine (used to reduce steroid use)
• In resistant cases, cyclosporine, cyclophosphamide, mycophenolate mofetil and IVIG can be used.
Three points are very important in dermatomyositis
I. The association of dermatomyositis with malignancies in adults is investigated, but this association is rare in children.
2. Subcutaneous calcifications and calcinosis are more common in JDM than in adults.
3. Aspiration pneumonia, which may occur as a result of proximal myopathy and dysphagia, is the most important major complication in these patients.