ICD-10-CM > M00-M99 > M60-M63 > M60 > M60.1 > M60.12 M60.12 Interstitial myositis, upper arm Non-Billable/Non-Specific Codes M60.121Interstitial myositis, right upper armM60.122Interstitial myositis, left upper armM60.129Interstitial myositis, unspecified upper arm