OBJECTIVE: To assess the long-term safety and tolerability and to monitor 
benefits of extended use of bimagrumab in individuals with sporadic inclusion 
body myositis (sIBM) who completed a single-dose core study.
METHODS: In this multicenter, open-label extension study, 10 adults received 
bimagrumab 10 mg/kg IV every 4 weeks up to 2 years (104 weeks). Safety (primary 
endpoint) was assessed by recording adverse events (AEs). Clinical benefits were 
assessed by changes from baseline in thigh muscle volume (TMV), lean body mass 
(LBM), 6-minute walk distance (6MWD), handgrip, and quadriceps strength.
RESULTS: Participants had a mean age of 70.1 (SD 10.4) years. All participants 
(n = 10) discontinued the treatment due to early termination of the study (n = 
7) or AEs (n = 3; myocardial infarction, esophageal carcinoma, and dementia, 
none of which were treatment related). The most common AEs were muscle spasms 
and falls (both 9 of 10, 90%), followed by diarrhea (6 of 10, 60%) and acne and 
skin eruption (both 5 of 10, 50%). At weeks 8 and 16, mean TMV increased from 
baseline by 4.1% (SD 4.3%) and 4.5% (SD 6.3%). Mean LBM increased from baseline 
and was sustained at 6.9% (SD 3.9%) at week 76. Means of 6MWD showed a 
progressive decline from baseline to week 76, during which there was a modest 
numerical increase in handgrip strength and no significant changes in quadriceps 
strength.
CONCLUSIONS: Long-term treatment up to 2 years with bimagrumab had a good safety 
profile and was well tolerated in individuals with sIBM. An increase in muscle 
mass was noted on a group level; however, there was no evidence of clinical 
improvement.
CLINICALTRIALSGOV IDENTIFIER: NCT02250443.
CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that for 
patients with sIBM, long-term bimagrumab treatment was safe and well tolerated 
and did not lead to functional improvement.