The diagnosis is based on

• Medical history of symptoms or proven pathology
  • Lungs
  • Muscles
  • Arthritis (Arthritis)
  • Skin
  • Antibodies
• Pulmonary abnormalities
• Myositis
• Antibodies
• Exclude another reason (Differential diagnosis)

Disease history

• Debut (time) for onset of symptoms: dry cough, dyspnea at physical stress

• Lungs

  • Dry cough
  • Dyspnea at physical stress
  • Quickly progressive symptoms from lungs (increase from week to week)?

• Muscles (Myositis)

  • Pain
  • Weakness
  • Dysphagia (esophagus affection)
  • Proximal (classical) and / or distal affection

Immunomodulatory treatment to date

• Methyl prednisolone (SoluMedrol)
• Prednisone (Maximum and actual dose)
• Cyclophosphamide (Sendoxan; treatment duration and dose), Rituximab (Rixathon, MabThera), Mycophenolate (CellCept), Azathioprine (Azathioprine), methotrexate, others)

Clinical examination

• Lungs

  • Crepitations over lungs by auscultation?

• Skin

  • Mechanic's Hands (Cracked dry skin on hands)
  • Gottron's sign or papules (red-violet color over MCP joints)
  • V-shaped sign (chest and throat) (Red-blue color)
  • Shawl-shaped characters (neck and back) (Red-blue color)
  • Heliotropic rash (eyelid)
  • Raynaud's phenomena (Three-phasic)

• Joint

  • 90-90 deformity in thumb
  • Rheumatoid arthritis like courses occur

• Muscles

  • Muscular atrophy and reduced force (rising from chair / squat without support?)
  • Weaker muscle strength (proximal) in the thighs, arms or neck?
  • Reduced walking function?

Laboratory tests

• Creatine kinase (CK) is usually moderately elevated
• AST and LD (usually elevated)
• Antibodies ( "Myositis-specific)
  • Jo-1, P1-7 or P1-12 (+ some very rare) are usually present
  • ANA (antinuclear antibody) of 50%
  • SSA (Ro 52) is often positive in low titer without at the same time Sjögren's syndrome eller SLE may be present

Supplementary Medical Examination

• Lung function tests (including DLCO)

• Radiological

  • HRCT examinations of lungs
  • X-ray examination may be normal even in case of major lung changes
  • MRI examination (with contrast) of proximal muscles, most of both thighs
    • MRI locates muscle groups with the most manifestations. Localization for biopsy (see below)
  • X-ray or manometry of esophagus (swallowing)

• Laboratory

  • Rutine (Hb, Erythrocyte Sedimentation Rate (ESR), CRP, leukocytes, platelets, liver enzymes, K, Na, Cl, Ca, Creatinine, TSH, T4, creatine kinaseCK)
  • Myositite specific autoantibodies (a-Jo-1 in 80-90%, Pl-7 and Pl-12 and others are less frequent)
  • Anti-SSA (Ro) antibody (as by Sjögren's syndrome og SLE) is not uncommon

• Capillaroscopy 

  • Pathological findings are somewhat less frequent than at Systemic sclerosis

• Muscle Biopsy

  • Will be performed if increased CK, edema on MRI, or positive EMG (electromyography).

Malignancy

• Malignancy investigations should be considered (especially in adult dermatomyositis)
  • Gynecological examination, CT abdominal examination, electrophoresis urine / serum, stool of blood test, colonoscopy, other investigations if clinical suspicion
  • Alternatively: PET / CT

Differential diagnosis

• Differential diagnoses of the antisynthetase syndrome are described here (in Danish)

Myositis (BINDEVEVSSYKDOMMER.no)

Antisynthetase syndrome, BINDEVEVSSYKDOMMER.no

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