Juvenile dermatomyositis (JDM) has a broad range of severity and is a serious disease requiring specialist assessment and management. JDM can present at any age, with characteristic skin involvement (malar rash, heliotrope rash over the eyelids, photosensitivity, vasculitis, nail fold capillary changes), and proximal muscle weakness which can present acutely or indolently with difficulty on stairs or fatigue on walking. Presentation may also include systemic symptoms such as malaise, fever, weight loss or anorexia. Arthritis, joint contractures and myalgia, dysphagia, dysphonia, dyspnoea, calcinosis and skin ulceration and oedema may also be present. Calcinosis (painful or painless lumps or sheets under the skin) are a feature of late diagnosis or poorly controlled disease. Chronic skin disease can result in Gottron's papules over the knuckles, elbows or knees. Patients may have involvement of bulbar muscles and chest wall which may result in risk of aspiration pneumonia.
The photograph below shows characteristic heliotrope rash over the eyelid
The photograph below shows characteristic malar rash (can be photosensitive)
The photograph below shows subcutaneous calcinosis in JDM
The photograph below shows typical Gottron's papules over the knuckles in JDM
The photograph below shows severe joint contracture and muscle wasting from chronic JDM that has not been treated optimally.
The radiograph below shows severe calcinosis around the knee in chronic JDM
Interstitial lung disease and gut vasculitis can occur with potential for severe morbidity and mortality. Many patients (1/3) will develop associated arthritis in the course of their disease. Unlike adult onset DM, JDM does not tend to be associated with malignancy: routine screening for malignancy in children with JDM is not necessary.
The diagnosis of JDM relies on clinical assessment and investigations (including elevated serum muscle enzymes, imaging and tests to exclude other differential diagnoses). However it is important to consider inherited myopathies which can also cause elevated muscle enzymes; there may not be a family history and any unusual features warrant further investigation which may include muscle biopsy. Notably, most children with JDM do not require electromyography or a muscle biopsy except where the presentation is atypical. Magnetic resonance imaging (MRI) of the muscles helps to identify muscle involvement and monitor disease activity; MRI is now regarded as diagnostic. Muscle biopsy may show inflammation, fibre necrosis and small vessel vasculitis but is not always required for diagnosis. Electromyogram (now rarely performed) shows myopathy / denervation.
The management of JDM is multidisciplinary. Treatment of JDM requires high dose corticosteroids, often given intravenously, frequently accompanied by methotrexate, although other medications such as intravenous immunoglobulin, cyclophosphamide or anti-cytokine (biologics) agents are used in severe or refractory disease. Any suspicion of bulbar of chest wall muscle involvement (weakness of speech or cough, difficulty in eating or swallowing or shortness of breath) warrant urgent specialist intervention. Speech and language therapist assessment is important as well as physiotherapy and specialist nurse input to optimise outcome and support patients and families. This is covered further in pmm-nursing.
Please watch the videos showing a 4 year old girl with JDM
Video 1 - proximal weakness before treatment ; Video 2 - improving proximal muscle strength on treatment (she is also cushingoid) ; Video 3 - further improvement and cushingoid features ; Video 4 - further improvement and no longer cushingoid (in remission)