Distribution and trajectory of direct and indirect costs of idiopathic inflammatory myopathies.

Objectives: To estimate the annual direct and indirect costs associated with Idiopathic Inflammatory Myopathies (IIM) over time, including the pre-diagnostic period.

Methods: A cohort of incident adult IIM patients (n = 673) was identified from the Swedish National Patient Register from 2010 to 2016 and matched with general population comparators (n = 3343). Follow-up started at IIM diagnosis and corresponding date in the general population. International Classification of Diseases codes (ICD-10) were used for IIM case definition. Costs were calculated using national register data.

Results: The costs related to IIM started to increase 2 years before diagnosis. In the year following diagnosis, the mean annual IIM cost was €21 639 compared to €4816 in the general population. Five years after diagnosis, the mean annual cost in the IIM cohort was €12 796. Outpatient visits, hospitalizations and productivity loss were the components driving the increment in overall annual disease-related expenditures. Indirect costs accounted for a significant portion of IIM long-term societal costs. The highest costs were found in individuals of working age with cancer-associated IIM.

Conclusions: The mean annual costs in IIM were 3 to 5 times higher than in the general population in the 5-year period following diagnosis. These costs started to increase long before diagnosis, were at their peak in the year post-diagnosis and remained elevated thereafter. Indirect costs contributed to a substantial portion of this increment. Early in the IIM disease course, clinicians and allied health professionals should aim to improve function, reduce damage and address barriers to return-to-work to mitigate these costs.