Background Polymyosit (PM) and dermatomyosit (DM) are rare systemic inflammatory diseases presenting with impaired muscle function which is usually assessed by the manual muscle test (MMT)-8 muscle groups. Quality of life is also reduced. The use of the disease-specific muscle endurance measure Functional Index-2 (FI-2) has indicated severely impaired muscle endurance in adult PM/DM and a majority of patients might not improve clinically relevant in muscle endurance one year after diagnosis. It is not known how muscle endurance develops over a longer period in these patients.
Objectives To study how muscle strength, muscle endurance and quality of life change over five years after diagnosis, and to investigate possible relationships between muscle impairment and quality of life in patients with adult PM/DM at 5-year follow-up.
Methods Data of muscle strength (MMT-8), muscle endurance (FI-2), and quality of life (SF-36, 0-100, 100 = good health) were retrieved from the Swedish Myositis Register (SweMyoNet) on patients followed at Karolinska University Hospital at one year (n=49) and five years (n=44) after diagnosis of adult PM or DM.
Results On a group level there was no change in muscle endurance (FI-2) at 5 years; median 27 (q1-q3 6-72) % of maximal score compared to 1-year follow-up 29 (17-61). Also, muscle strength (MMT) was unchanged at 5 years; 98 (86-100)% of maximal score compared to 1-year 96 (88-99)%. Six out of 26 patients improved in FI-2 ≥20% (of whom 4 ≥70%) and 11/26 patients worsened ≥20% (of whom 6 ≥50%, of whom 4 ≥70%) at 5 years. 1/28 patients improved in MMT-8 ≥20%, while none worsened. The group (n=33) had significantly more pain (SF-36 Bodily pain), 51 (41-84) at 5 years compared to 1-year, 74 (51-84) (p<0.05) while the remaining domains were unchanged. FI-2 correlated strongly to SF-36 Physical Function (PF) (rs=0.80) and moderately to Role-Physical (RP) (rs=0.50), Social function (SF) (rs=0.52) and Role Emotional (RE) (rs=0.54). The MMT correlated equally strong to PF, with moderate correlations to General Health (rs=0.63), SF (rs=0.58) and RE (rs=0.54).
Conclusions Forty-two % of patients worsened in muscle endurance while 23% had a clinically relevant improvement while most patients remained unchanged in muscle strength between one and five years after start of immunosuppressive treatment. Patients scored worse pain after 5 years compared to one year post treatment-start. The objective assessments FI-2 and MMT correlated strongly to self-reported quality of life (physical function). These data are preliminary due to large number of missing data, but raise concern and the need for systematic follow-up of these variables in larger cohorts of myositis patients.
Disclosure of Interest None declared