Background/Purpose: Poly- and dermatomyositis (PM/DM) are idiopathic inflammatory muscle diseases characterized by reduced muscle function. Oral glucocorticoids and DMARD’s are the usual treatment options and physical exercise plays an important role in the treatment as well. Despite an often beneficial effect of treatment, most patients are left with sustained muscle impairment and reduced quality of life. It is not known how muscle impairment differ between patients with newly onset PM/DM and patients with established PM/DM. The aim of this study is to investigate muscle function as to maximal isometric strength (MVIC) and isometric muscular endurance (ME) in patients with newly onset, active and established PM/DM. A further aim is to investigate possible correlations between muscle function and health related quality of life (HRQoL).

Methods: All patients diagnosed with PM or DM (n=5, all female) during 170901 and 180401 at Karolinska University hospital in Solna who met the inclusion criteria were asked to participate. Patients with established PM/DM (n=6, all female) where identified through patient register at the same clinic, selected to match recent onset disease group as to age and gender. A dynamometer from Biodex was used to assess MVIC and ME starting with three warm-up 4-sec contractions followed by three similar maximal contractions, all with a 3-minute rest in-between. Thereafter six sets of twelve submaximal repetitions, starting on 20 % of MVIC and increasing by 10 %/set, finishing on 70 % of MVIC. Each set ended with a new maximal contraction registered as percentage of initial MVIC. The participants reported HRQoL using SF–36. Statistical significance was set to p<0.05, Mann-Whitney U-test was used to compare groups and Spearman’s rho for correlations.

Results: Median age for patients with recent onset PM/DM was 36 (min–max 19–64) years and for established disease 61 (42–66) years. Diagnosis duration was 4 (1–6) months and 126 (85–433) for the two groups, respectively. Patients with recent onset disease had a median MVIC of 73 (53–127) Nm and patients with established disease had 58 (41–82) Nm (p=0.22). ME were 83 (63–94) % and 91 (85–98) % for patients with recent onset disease and established PM/DM, respectively (p=0.08). The correlations between ME and General Health was (r_s=0.54, CI=-0.08–0.87) with correlations to Physical Function, Physical Role Function, and Social Function varying between (r_s=0.40, CI=-0.26–0.81) and (r_s=0.48, CI=-0.17–0.84). Correlations between MVIC and Vitality, Physical Role function, Emotional Function and Social Function varied between (r_s=-0.49, CI=-0.84–0.16) and (r_s=-0.34, CI=-0.78–0.33). Correlations to remaining domains were lower.

Conclusion: No significant differences were found between the groups regarding MVIC and ME. However, there was a trend towards reduced ME in patients with recent onset PM/DM compared to established disease. Correlations between muscle function and HRQoL were moderate at best. Further research is needed with more patients to reach statistical power and improved matching of patients and controls.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/muscle-function-and-health-related-quality-of-life-in-patients-with-polymyositis-and-dermatomyositis/