JDM
Biopsy and EMG studies are frequently avoided in diagnosing children with juvenile dermatomyositis. Other diagnostic studies, including MRI, are used more frequently.
A diagnosis of juvenile dermatomyositis should be considered for patients presenting with the following criteria:
- Symmetrical muscle weakness in the shoulders/upper arms or hips/upper legs and trunk
- Characteristic dermatomyositis skin rash:
- Heliotrope rash – a red/purple rash with swelling on the upper eyelid
- Periungual telangiectasias – dilated capillaries at the skin folds around the fingernails, appearing as small red dots
- Gottron’s sign or papules – red/purple hardened or eroding areas of skin on the upper surface of finger joints or over the elbows or knees
- Shawl sign, V-sign, and holster sign – characteristic red, sometimes raised rashes distributed in a “shawl” pattern over the shoulders, arms, and upper back, in a V-shaped pattern over the front of the neck and chest, and over the outside of the hip
- Elevated muscle enzymes (aldolase, creatine kinase, transaminase)
- Myopathic changes on EMG (if done)
- Short, small, low-amplitude polyphasic motor unit potentials
- Fibrillation potentials, even at rest
- Bizarre high-frequency repetitive discharges
- Muscle pain on grasping or spontaneous pain
- Positive for any of the myositis-specific autoantibodies
- Nondestructive arthritis or arthralgias
- Signs of systemic inflammation
- Fever
- Elevated serum C-reactive protein (CRP) level, or
- Accelerated erythrocyte sedimentation rate (ESR)
- Abnormalities on MRI suggestive of inflammatory myositis
- Skin biopsy (if done) demonstrates reduced capillary density, deposits of membrane attack complex on small blood vessels along the dermal-epidermal junction, and within the walls of dermal blood vessels
- Other findings (calcinosis, dysphagia, dysphonia, skin ulcerations)
Further testing
Other blood tests may be used to diagnose or monitor juvenile myositis:
- Antinuclear antibody (ANA)
- Myositis-specific antibodies (MSA), i.e. anti-Jo-1, anti-SRP
- Myositis-associated antibodies (MAA), i.e. anti-PM-Scl
- Flow cytometry
- Neopterin (a marker for immune system activation)
- von Willebrand factor antigen (factor VIII-related antigen)
Other diagnostic tools may include:
- MRI to identify signs of inflammation and edema
- Nailfold capillaroscopy to study possible decreased density of nailfold capillary loops (dropout) or dilation of the capillaries
- Muscle ultrasound
- Manual muscle testing (MMT) and other tests of muscle strength
- Tests for physical function, such as Childhood Health Assessment Questionnaire (CHAQ) and Childhood Myositis Assessment Scale (CMAS)