Measuring Adherence and Outcomes in the Treatment of Patients With Multiple Sclerosis

Context: Both adherence and outcomes are more difficult to measure in patients with multiple sclerosis (MS) than in patients with diseases such as hypertension, for which most medications are taken orally and surrogate outcomes (eg, blood pressure) are routinely collected. Objectives: To characterize the adherence and outcomes of patients with MS within a large integrated health system and to assess the relationship between adherence and outcomes. Study Design: Retrospective review of adherence and health care utilization outcomes via electronic health records and claims (2004-2013) combined with a prospective survey regarding adherence and functional outcomes (2012-2013). Methods: Retrospectively, medication possession ratios were calculated, and adherence groups were compared regarding health care utilization and costs. Prospectively, patients were recruited to complete questionnaires to measure self-reported adherence (SRA) and MS-specific outcomes, including the Multiple Sclerosis Impact Scale (MSIS), the Kurtzke Expanded Disability Status Scale (EDSS), and the Treatment Satisfaction Questionnaire for Medication (TSQM). Regression was used to statistically test for differences in these outcomes among adherence groups. Results: A total of 681 patients were studied. Most patients (307 of 375 [82%] in the retrospective cohort and 244 of 306 [89%] in the prospective cohort) had greater that 80% adherence to their MS medications. Mean inpatient days per patient for MS-related admissions was highest for high-adherence than for intermediate and low-adherence patients (0.52 vs 0.23 and 0.34, respectively; P<.001), but no other associations between adherence and health care utilization were found. Mean outpatient costs and total costs were lowest for the low-adherence group, suggesting that higher adherence may not guarantee cost savings overall. Patients with intermediate and high self-reported adherence showed significantly better mean scores than patients with low adherence on several MS outcomes, including EDSS (4.1 and 4.2 vs 4.8, P<.05), MSIS physical function (33 and 35 vs 41, P<.05), and TSQM Global Satisfaction (75 and 78 vs 70, P<.05). Conclusions: The findings of this study indicate that patients with MS are mostly adherent to their existing treatments. Patients with greater medication adherence may have increased cost, but their physical outcomes are better. This finding may shed light on other chronic disease entities and how we view the success of treatments.