1. A B Anti-SRP-Myopathy Non-severe Severe*
± IV steroids g/d, 3-5 d
oral steroids 1 mg/kg/d
IV steroids g/d, 3-5 d
oral steroids 1 mg/kg/d
At the same time or within 1 month, start 2nd or 3rd agent
Oral/sc Methotrexate° (0.3 mg/kg/w, max 15 & 25 mg/w
in child & adult, respectively)
Rituximab£,§ 750 mg/m2 (max 1g) D1 + D7-D15
eventually
IVIG 2 g/kg/m, 3-6 times
Initial treatment
If no adequate response within 6m: reconsider Rituximab
(if not started) and keep giving other treatments.
Anti-HMGCR-Myopathy B
Non-severe
Severe*
± IV steroids g/d, 3-5 d
oral steroids 1 mg/kg/d
IV steroids g/d, 3-5 d
oral steroids 1 mg/kg/d
At the same time or within 1 month, start 2nd or 3rd agent
Oral/sc Methotrexate° (0.3 mg/kg/w, max 15 & 25 mg/w
in child & adult, respectively)
IVIG 2 g/kg/m, 3-6 times (possibly alone in case of steroids
contraindication or intolerance)
eventually
Rituximab£ 750 mg/m2 (max 1g) D1 + D7-D15
Initial treatment
If no adequate response within 6m: reconsider Rituximab
(if not started) and keep giving other treatments.

2. Anti-SRP & anti-HMGCR-Myopathy
Taper oral steroids to the lowest dose as tolareted or as soon as possible (regarding the maximum benefit)
Continue Methotrexate at least 2 years of well-controlled disease (slowly tapered later: 2.5 mg/w each month)
Continue Rituximab every 6 months, at least 2 years of well-controlled disease
If started IVIG are stopped or tapered, as tolerated.Nota bene: many HMGCR+patients may required IVIG
Maintenance
treatment
Figure X: Consensus for the initial treatment of IMNM
A. Anti-SRP-myopathy. B. Anti-HMGCR myopathy
IV: intavenous, IVIG: intravenous immunoglobulins, d: day, m: month, sc: sub-cutaneous,*: walking difficulties and/or dysphagia, °: Azathioprine or Mycophenolate mofetil in case of Methotrexate intolerance, £: rigourous data from the literature are however missing, §: along with Methotrexate, especially in severe cases