Juvenile dermatomyositis

Juvenile dermatomyositis (JDM) is the most common inflammatory myopathy in pediatrics. Inflammatory myopathies include a heterogeneous group of diseases characterized by the presence of weakness and inflammatory infiltrate in muscle biopsy.

It is a rare disease, with an incidence of approximately 3-4 cases per million children per year. It is estimated that 16-20% of all dermatomyositis begin in pediatric age, with a peak incidence between 5 and 14 years of age. It is more frequent in girls.

It predominantly affects skin and striated muscle but can affect the gastrointestinal tract, heart and other organs. It may be accompanied by systemic symptoms such as fever, fatigue or weight loss.

Depending on its course, three patterns of disease can be distinguished:

• Monophasic form: occurs in approximately one third of patients. It is characterized by a single episode of illness.
• Chronic form: Occurs in approximately 50% of patients. Symptoms persist or recur with tapering of immunosuppressive therapy.
• Polycyclic form: Episodes of disease alternating with episodes of remission.

The use of corticosteroids has decreased mortality to below 3% although morbidity remains high, estimated to be present in 70-80% of patients.

The goal of treatment is symptom control and prevention of complications. Early staged treatment decreases disease activity and improves long-term prognosis. Delay in diagnosis is associated with a worse prognosis.