Background/Purpose:

Most patients with polymyositis (PM) and dermatomyositis (DM) develop sustained muscle impairment. The aim of this study was to evaluate the muscle endurance (Functional Index 2, FI-2), muscle strength (MMT-8) and disease activity (selected 6-item core set measures) at 6 and 12 months after PM/DM diagnosis onset (baseline).

Methods:

72 patients, 40 with PM and 32 with DM, diagnosed 2003-2010 who performed the FI-2 and the MMT at baseline were included. They had median age md (Q1-Q3) 55 (41-70) years and md diagnosis duration 0 (0-1) months. 44 were women and 28 were men, 34 patients had md 50 (30-60) mg of prednisone/day, 38 were without medication. Mixed Linear Model with time as fixed variable was used with the Bonferroni after test to compare genders and diagnosis at different time points. Individually patients were identified as responders improving > 20% or worsening > 20% in the FI-2 / MMT at follow-ups compared to baseline. Significance level was set to 0.05.

Results:

The group had md 27 (8-60) % of FI-2 maximal score and md 94 (83-99) % of MMT maximal score at baseline (p<0.000) with no significant change at 6 or 12 months compared to baseline. Men had higher FI-2 scores md 50% (22-84) of maximal score at baseline, 84% (17-88) at 6 months, 61% (27-90) than women md 13% (5-42) at baseline, 19% (6-47) at 6 months and 18% (10-46) at 12 months (p<0.000) and men improved more over time in FI-2 than women (p<0.000). 44% of 41 patients were responders and 22% worsened in FI-2 score at 6 months and 49% of 45 patients were responders and 29% worsened at 12 months. 19 % of 37 patients were responders in MMT score at 6 months and 15% of 33 patients were responders at 12 months, no patient worsened. PM and DM patients improved in VAS physician global disease activity at 6 and 12 months compared to baseline (p<0.034, p<0.002) but patients with PM had significantly higher scores 10 (5-30) mm at 12 months compared to DM md 6 (4-15) mm (p<0.043). The men had significantly reduced global extra-muscular VAS scores at 6 and 12 months compared to baseline (p<0.011, 0.021) and women remained unchanged. Patients with DM had reduced extra-muscular disease activity at 6 and 12 months (p<0.022, p<0.021) while there was no change in PM.

Conclusion:

Male patients seem to improve more over time than women in muscle endurance and improve in extra-muscular disease activity while women do not. Patients with DM seem to have lower disease activity compared to PM and DM patients improve in extra-muscular disease activity while patients with PM do not. Between 44-49 % were responders and 22-29 % worsened in muscle endurance while 15-19% were responders and none worsened in muscle strength.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/outcome-of-muscle-function-and-disease-activity-in-patients-recently-diagnosed-with-polymyositis-and-dermatomyositis-preliminary-results-of-a-1-year-follow-up-registry-study/