Inflammatory myopathies: polymyositis (PM), dermatomyositis (DM) and necrotising autoimmune myopathy (NAM)

Version: 3.2
Published: 30 March 2020
Condition for which Ig has an established therapeutic role.

• In adults, biopsy-proven PM, DM or NAM; or in children, diagnostic muscle biopsy or demonstration of the following three characteristics:
  • characteristic rash;
  • elevated muscle enzymes;
  • typical MRI scan abnormalities

• Significant muscle weakness, as measured in an adult by a Medical Research Council (MRC) sum score of 55 points or less; or in a child by the Childhood Myositis Assessment Scale (CMAS) to a value of 44 points or less
• OR
• Significant dysphagia limiting dietary intake with involvement of pharyngeal muscles as demonstrated by video-fluoroscopy unless speech pathology assessment indicates that video fluoroscopy in the particular patient is associated with an unacceptable risk of aspiration

• Unresponsive to corticosteroid treatment
• OR
• Unable to tolerate corticosteroids due to unacceptable side effects or significant toxicity
• OR
• Corticosteroid therapy is contraindicated

• At least two immunosuppressant agents (one of which should be corticosteroids) have been used and are ineffective or have been commenced but not yet become effective
• OR
• Immunosuppressant medication is contraindicated

IVIg should be used for up to four months (induction plus three maintenance cycles) before determining whether the patient has responded. If there is no benefit after this treatment, IVIg therapy should be abandoned.
 
Review by a neurologist, rheumatologist, or  immunologist is required within four months and annually thereafter. Cessation of Ig therapy should be considered at each review once stable or when alternative immunosuppressant agents have been commenced and are effective and the patient is stable.

Documentation of clinical efficacy is necessary for continuation of Ig therapy.

IVIg should be used for up to four months (induction plus three maintenance cycles) before determining whether the patient has responded. If there is no benefit after this treatment, IVIg therapy should be abandoned.
 
Review by a neurologist, rheumatologist, or immunologist is required within four months and annually thereafter. Cessation of Ig therapy should be considered at each review once stable or when alternative immunosuppressant agents have been commenced and are effective and the patient is stable.

Documentation of clinical efficacy is necessary for continuation of Ig therapy.
 
Clinical effectiveness of Ig therapy may be assessed by:
 

On review of the initial authorisation period

• Improvement in muscle weakness compared to the qualifying assessment as measured in adults by an increase in the Medical Research Council (MRC) sum score; or in children by an increase in the Childhood Myositis Assessment Scale (CMAS) score of at least two points
• OR
• Improvement in symptoms of dysphagia compared to the qualifying assessment as assessed by speech pathology, tolerance of food textures and/or reduced episodes of aspiration

On review of a continuing authorisation period

• Stabilisation or continued improvement in muscle weakness and symptoms as measured by the Medical Research Council (MRC) sum score or Childhood Myositis Assessment Scale (CMAS) score greater than or equal to the previous review score
• OR
• Patient with severe disease continues to report post infusion improvement with end-of-cycle deterioration and additional immunosuppressant agents have been commenced
• OR
• Stabilisation of, or continued improvement in symptoms of dysphagia compared to the previous review assessment as measured by speech therapy, improved tolerance of food texture and/or reduced episodes of aspiration

• A trial of Ig weaning towards cessation of Ig therapy is planned for patients who are clinically stable to identify those in remission or a reason provided as to why a trial is not planned

For stable patients on maintenance treatment, review by a specialist is required at least annually. Most patients do not require long term therapy and progressive reduction in dosing should be considered.
 
Cessation of Ig therapy should be considered once alternative immunomodulating agents have been commenced and are effective and the patient is stable.

• Induction Dose (IVIg) - 2 g/kg in 2 to 5 divided doses.
• Maintenance Dose (IVIg) - 0.4–1 g/kg, 4–6 weekly. A maximum total dose of 1g/kg may be given in any four week period. This can be administered in weekly divided doses, provided the total maximum is not exceeded.