Table 2

Recommendations regarding diagnosis

LSAgreement (%)
(a) General recommendations
In the absence of cutaneous signs and/or failure to respond as expected to therapy, alternative diagnoses should be considered including metabolic or mitochondrial myopathies and dystrophies.4D100
In every patient in whom a diagnosis of JDM is considered, the following list of investigations should be considered:
  1. Muscle enzymes—including creatinine phosphokinase (CPK), LDH, AST (SGOT), ALT (SGPT), adolase (if available)

  2. Full blood count and blood film

  3. ESR (or plasma viscosity) and CRP

  4. Myositis-specific and myositis-associated antibodies

  5. Renal function and liver function tests

  6. Infection screen (for differential diagnosis)

  7. Investigations for alternative systemic causes of myopathy including endocrine disorders (especially thyroid function), electrolyte disturbances, vitamin D deficiency

  8. Further tests for metabolic/mitochondrial myopathies (especially in the absence of rash/atypical presentation)

  9. Urine dipstick (with further evaluation if positive for protein)

  10. Nailfold capillaroscopy

  11. Echocardiogram and ECG

  12. Pulmonary function tests (chest X-ray and HRCT if concern)

  13. MRI of muscles (+quantitative ultrasound)

  14. EMG (particularly if suspicion of neuropathy/disorder of neuromuscular junction)

  15. Muscle biopsy (especially in the absence of rash/atypical presentation)

  16. MRI brain if neurological involvement suspected

  17. Abdominal ultrasound scan

(b) Specific recommendations
Assessment of muscle involvement
 Both muscle strength and function should be tested at diagnosis and follow up by formal validated measures, such as the MMT8 and the CMAS.2a-3B–C100
 MRI can be used to aid diagnosis of JDM.2BB100
 MRI can be used to help monitor disease activity.2BB100
 When used, MRI should be carried out by defined protocols that enhance detection of muscle inflammation, such as T2 weighted/STIR sequences.3C100
 MRI should be interpreted by an expert radiologist.4D100
 A muscle biopsy should be done in all cases where the presentation of JDM is atypical; in particular in the absence of rash/skin signs.4D100
 If a muscle biopsy is performed for diagnosis of JDM, a standardised JDM biopsy score tool should be used to quantify severity of histological abnormalities.2BB100
 Expert histopathological opinion is required to define features of inflammation in JDM muscle biopsy.4D100
 When doing a muscle biopsy, there is insufficient evidence to recommend a needle biopsy as opposed to an open biopsy in children.3C100
 In cases where MRI or muscle biopsy is not possible, increased muscle echo intensity on muscle ultrasonography (when performed by an experienced sonographer) may be indicative of myositis.2BC82
 Swallow function should be formally assessed in every patient. The assessment may include a speech and language therapy assessment, video fluoroscopy/barium studies.3C100
 EMG or nerve conduction velocity should be considered to differentiate myopathy from neuropathy when diagnosis of JDM is uncertain.4D100
 EMG does not detect metabolic myopathies reliably and further workup is required if this diagnosis is suspected.3D100
Assessment of skin involvement
 Assessment of nailfold capillaries should be used to aid diagnosis of JDM.2B100
 At time of diagnosis or disease flare, standardised nailfold capillaroscopy assessment is recommended. During follow-up, assessment of nailfold capillaries should be performed regularly.3C100
 A formal CAT should be used to aid diagnosis of JDM.4D100
 A formal CAT should be used to monitor skin disease activity over time.2BB100
 Skin tools may include the DAS (skin), MITAX (skin) or CAT.4D100
Assessment of lung involvement
 All patients with JDM should have an assessment of lung involvement at time of diagnosis.3C100
 Assessment should include pulmonary function tests, including CO diffusion. If pulmonary function tests are indicative of interstitial lung disease, further investigations (CXR/ HRCT) are needed.4D100
Assessment of cardiac involvement.
 All patients with JDM should have echocardiography and ECG at diagnosis.4D94
 Patients at particular risk of cardiac dysfunction should have repeated cardiac evaluation. Risk factors include hypertension, high disease activity 1 year post diagnosis, long-term high corticosteroid burden or chronic ongoing active disease.2BB100
Assessment of calcinosis
 Calcinosis should be looked for in all patients with JDM.4D94
 Plain radiographs may be used for the evaluation of calcinosis.3C100
Autoantibodies and biomarkers
 We recommend use of muscle enzymes (CPK, LDH, AST) for diagnosis and disease monitoring in JDM, although it must be recognised muscle enzymes may be normal despite active disease.4D100
 Measurement of von Willebrand factor does not provide any additional information for diagnosis of JDM.3C100
 There is no significant diagnostic benefit gained from measurement of antinuclear antibody in JDM.4D100
 Measurement of myositis-specific autoantibodies (such as anti-TIF 1-γ (p155), anti-NXP2/(p140/MJ), anti-MDA5 and anti-SRP) should be considered, when available.2A-3B–C100
 In patients with overlap features, measurement of myositis-associated-antibodies such as anti-PmScl, anti-U1-RNP, anti-La (‘SSB’), anti-Ro (‘SSA’) and anti-Sm may be helpful to clarify the diagnosis.4D100
 Further validation studies are recommended to define the use of more sensitive biomarkers in JDM.4D100
  • Agreement indicates percentage of experts that agreed on the recommendation during the final voting round of the consensus meeting.

  • 1A, meta-analysis of randomised controlled trial; 1B, randomised controlled study; 2A, controlled study without randomisation; 2B, quasi-experimental study; 3, descriptive study; 4 expert opinion; A, based on level 1 evidence; B, based on level 2 or extrapolated from level 1; ALT, alanine aminotransferase; AST, aspartate aminotransferase; C, based on level 3 or extrapolated from level 1 or 2; CAT, Cutaneous Assessment Tool; CMAS, Childhood Myositis Assessment Scale; CO, carbon monoxide; CRP, C-reactive protein; CXR, chest X-ray; D, based on level 4 or extrapolated from level 3 or 4 expert opinion; EMG, electromyogram; ESR, erythrocyte sedimentation rate; HRCT, high-resolution computed tomography; L, level of evidence; LDH, lactate dehydrogenase; MITAX, myositis intention to treat activity index; MMT, Manual Muscle Test; RNP, anti-ribonuclear protein; S, strength of recommendation; SGOT, Serum Glutamic-Oxaloacetic Transaminase; SGPT, Serum Glutamic-Pyruvic Transaminase; SRP, signal recognition particle; SSA, Ro antibodies; SSB, Sjögren's syndrome type B antibodies; STIR, Short-TI Inversion Recovery.