BACKGROUND: Relapses are the hallmark of multiple sclerosis (MS). Analyses have shown that the cost of MS increases during periods of relapse. However, results are inconsistent between studies, possibly due to different study designs and the different implications of relapses with respect to patient characteristics.

OBJECTIVES: The aims were to estimate and describe direct and indirect relapse costs and to determine differences in costs with respect to patient characteristics. Furthermore, we describe the pharmacoeconomic impact during the relapse follow-up.

METHODS: Data were extracted from two German, multicenter, observational studies applying a validated resource costs instrument. Relapse costs were calculated as the difference in quarterly costs between propensity score (PS)-matched patients with and without relapses (1:1 ratio). For relapse active patients, we additionally calculated the difference between quarterly costs prior to and during relapse and determined costs in the post-relapse quarter.

RESULTS: Of 1882 patients, 607 (32%) presented at least one relapse. After PS-matching, 597 relapse active and relapse inactive patients were retained. Relapse costs (in 2019 values) ranged between €791 (age 50 + years) and €1910 (disease duration < 5 years). In mildly disabled and recently diagnosed patients, indirect relapse costs (range €1073-€1207) constantly outweighed direct costs (range €591-€703). The increase from prior quarter to relapse quarter was strongest for inpatient stays (+ 366%, €432; p < 0.001), day admissions (+ 228%, €57; p < 0.001), and absenteeism (127%, €463; p < 0.001). In the post-relapse quarter, direct costs and costs of absenteeism remained elevated for patients with relapse-associated worsening.

CONCLUSION: A recent diagnosis and mild disability lead to high relapse costs. The results suggest the necessity to incorporate patient characteristics when assessing relapse costs.