Eligibility Criteria

• Participants aged 7 older
• Meets Bohan and Peter criteria, as modified by the International Myositis Assessment and Clinical Studies Group (IMACS), for probable or definite DM or JDM
• Has extensive calcinosis, defined as calcinosis involving at least 2 extremities or the torso
• Has moderate to severe calcinosis, defined as having a calcinosis activity visual analogue scale score of greater than or equal to 3.5 cm out of 10 cm
• Is willing and able to comply with the requirements of the protocol and to undergo all testing
• Can have IV access established to receive study infusions
• Myositis disease activity is stable
• Medications for myositis are stable for at least 6 weeks prior to study entry
• Men and women of reproductive potential must agree to use a reliable form of birth control during the 62-week duration of the study
• Subjects or their legal guardian must sign a written informed consent
  • Stable myositis disease activity will be defined by physician global and patient/parent global VAS that are < 4 cm, as well as creatine kinase (CK), lactate dehydrogenase (LDH), aldolase, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) that are less than or equal to 2X upper limit of normal (ULN).
  • If a patient has a medication for myositis changed in this window for reasons besides their myositis activity and has returned to their baseline medication use prior to enrollment they will still be eligible.