Predictive value of early magnetic resonance imaging measures is differentially affected by the dose of interferon beta-1a given subcutaneously three times a week: an exploratory analysis of the PRISMS study

BACKGROUND: On-treatment magnetic resonance imaging lesions may predict long-term clinical outcomes in patients receiving interferon β-1a. This study aimed to assess the effect of active T2 and T1 gadolinium-enhancing (Gd+) lesions on relapses and 3-month confirmed Expanded Disability Status Scale (EDSS) progression in the PRISMS clinical trial. METHODS: Exploratory analyses assessed whether active T2 and T1 Gd + lesions at Month 6, or active T2 lesions at Month 12, predicted clinical outcomes over 4 years in PRISMS. RESULTS: Mean active T2 lesion number at Month 6 was significantly lower with interferon beta-1a given subcutaneously (IFN β-1a SC) 44 μg and 22 μg 3×/week (tiw) than with placebo (p < 0.0001). The presence of ≥4 versus 0 active T2 lesions predicted disability progression at Years 3–4 in the IFN β-1a SC 22 μg group only (p < 0.05), whereas the presence of ≥2 versus 0–1 active T2 lesions predicted disability progression in the placebo/delayed treatment (DTx) (Years 2–4; p < 0.05) and IFN β-1a SC 22 μg groups (Years 3–4; p < 0.05). Greater active T2 lesion number at 6 months predicted relapses in the placebo/DTx group only (≥4 vs. 0, Years 1–4; ≥2 vs. 0–1, Years 2–4; p < 0.05), and the presence of T1 Gd + lesions at 6 months predicted disability progression in the IFN β-1a SC 44 μg group only (Year 1; p < 0.05). The presence of ≥2 versus 0–1 active T2 lesions at 12 months predicted disability progression over 3 and 4 years in the IFN β-1a SC 44 μg group. CONCLUSION: Active T2 lesions at 6 months predicted clinical outcomes in patients receiving placebo or IFN β-1a SC 22 μg, but not in those receiving IFN β-1a SC 44 μg. Active T2 lesions at 12 months may predict outcomes in those receiving IFN β-1a SC 44 μg and are possibly more suggestive of poor response to therapy than T2 results at 6 months. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12883-018-1066-8) contains supplementary material, which is available to authorized users.