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01-03-2022 | Rheumatology | Highlight | Article

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Mixed results for branched-chain amino acids in polymyositis, dermatomyositis

Author: Laura Cowen

medwireNews: Branched-chain amino acid (BCAA) supplementation has no impact on muscle strength or clinical response in people with polymyositis or dermatomyositis (PM/DM) but may improve dynamic repetitive muscle function, Japanese study data show.

The phase 2/3 BTOUGH trial included 47 treatment-naïve adults with PM/DM who were randomly assigned to receive the BCAA supplement TK-98 (n=24) or placebo (n=23) in addition to conventional treatment for 12 weeks.

Individuals in the intervention group took two packages of TK-98 (4.15 g/pack) orally three times per day, with each package containing L-isoleucine 952 mg, L-leucine 1904 mg, and L-valine 1144 mg (molar ratio 1:2:1.35).

Naoki Kimura (Tokyo Medical and Dental University) and co-investigators report in Rheumatology that, at 12 weeks, the mean change in average manual muscle test (MMT) score was similar between the two groups.

Specifically, the score increased by an average 0.70 points from a baseline of 7.97 in the TK-98 group and by an average 0.69 points from 7.84 points at baseline in the placebo group.

Clinical responses at 12 weeks, evaluated using 2016 American College of Rheumatology/EULAR criteria, were also similar between the groups. All participants achieved a minimal improvement, 82.4% and 83.3% of the TK-98 and placebo groups, respectively, achieved a moderate improvement, while 29.4% and 38.9% achieved a major improvement.

Conversely, the researchers found that individuals who received TK-98 had significantly greater increases in functional index scores for bilateral shoulder flexion at 12 weeks than those who received placebo, at 27.9 versus 12.8 points for the right shoulder, and 27.0 versus 13.4 points for the left shoulder. There was no difference between the groups, however, in functional index scores for head lift or hip flexion.

Of note, 13 patients from the TK-98 group and 12 from the placebo group, who all had an average MMT score below 9.5 points at 12 weeks, were enrolled in an open label extension study for a further 12 weeks. At the end of this period, there was still no difference between the two groups in the change in mean MMT, with both groups showing constant improvement over time.

Kimura and co-authors conclude: “Although the primary endpoint was not achieved and official approval [for the use of TK-98 in this setting] could not be gained, this trial is unique in that the effect of BCAAs has been evaluated for the first time for the treatment of muscle weakness in PM/DM patients.”

They add: “As data from humans are limited, we hope that revised trials will proceed with suitable primary endpoints including the evaluation of muscle endurance and with optimized drug formulations.”

medwireNews is an independent medical news service provided by Springer Healthcare Ltd. © 2022 Springer Healthcare Ltd, part of the Springer Nature Group

Rheumatology 2022; doi:10.1093/rheumatology/keac101