Inclusion Criteria:  Ages 40 years and older Fulfills ENMC 2011 criteria of clinically definite or probable sporadic Inclusion body myositis (sIBM) Disease onset is within the past 10 years of the time of Baseline visit Able to participate and comply with study related procedures Able to provide written consent  Exclusion Criteria:  Current or very recent use (within last 6 months of the Baseline visit) of immunomodulation or immunosuppression therapy. Current or very recent use (within last 90 days of the Baseline visit) of an investigational medication or therapy. Co-existing significant medical or surgical conditions that, in the opinion of the investigator, will influence study participation or alter natural history.