Background Patients with adult polymyositis (PM), dermatomyositis (DM) and inclusion body myopathies (IBM) have reduced quality of life. Fatigue is an often disabling symptom in other inflammatory rheumatic conditions such as rheumatoid arthritis, however the contribution of fatigue on quality of life in patients with myositis is largely unknown.
Objectives To evaluate fatigue severity in PM, DM and IBM and to compare with population-based reference values, to evaluate a possible difference in fatigue between the myositis entities and gender, to evaluate correlations between fatigue and muscle function, disease activity and other aspects of quality of life and to study how fatigue develops over time.
Methods All patients registered in the Swedish Myositis register at the Karolinska University Hospital, n=80 (PM, n=46, DM, n=27, IBM, n=7) (55 women/ 25 men) who had completed the SF-36 survey during 2013 during a yearly check-up were included in this study. They had a median age of 62 (q1-q3 54-70.5) years, a median diagnosis duration of 8 (4.5-15.5) years and a median disease activity of 6 (0-15) mm (VAS physician's global assessment). Data on fatigue (SF-36 Vitality, 0-100 where 100 equals no fatigue), and muscle endurance (Functional Index 2, FI-2) were also collected. All patients who had completed the SF-36 survey at both 2009 and 2013 (n=41) were included to study how fatigue changes over time.
Results Patients had worse fatigue on the SF-36 Vitality, (median 50 (30-70)/mean 50±26) compared to population-based reference values (mean 67±20) (p<0.001). There was no difference in fatigue between patients with PM, DM and IBM (medians 48 (30-70), 50 (35-80) and 45 (35-50), respectively or between men, 50 (30-80) and women 50 (35-70). Correlations between the SF-36 Vitality and the other SF-36 domains varied between rs=0.54-0.75 with highest correlations to Mental health (rs=0.75) and Social function (rs=0.66). Correlations between the SF-36 Vitality and the FI-2, the HAQ and the physician VAS varied between rs=0.46-0.48 with lower correlations to prednisolone dose, diagnosis duration and age (rs=0.35, 0.01, <0.01, respectively). There was no significant change in fatigue over five years, median 50 (35-72.5) compared to 45 (20-60).
Conclusions Patients with PM, DM and IBM have significantly worse fatigue than the reference population, with no difference between sub-diagnosis and gender. Fatigue correlated best to mental health and social function. Fatigue scores were unchanged over five years. Fatigue seems to have an impact on quality of life and function in adult myositis and needs to be addressed in clinical care and should be a subject for future research.
Disclosure of Interest None declared