Biogen Idec Inc. and Elan Corporation, plc announced a global Phase 3b study, ASCEND, that is being conducted to evaluate the effectiveness of TYSABRI as a treatment for secondary-progressive multiple sclerosis (SPMS). Patients with RRMS typically experience unpredictable relapses; the time between relapses is characterized by full or partial recovery and a lack of disease progression. SPMS is characterized by a steady progression of nerve damage, symptoms and disability, but the exact reasons for the progression are unknown. The potential for greater disease burden in SPMS typically includes decreased mobility, impaired activities of daily living, loss of independence and reduced quality of life. The ASCEND study is part of the ongoing commitment of both Biogen Idec and Elan to find ways to improve the well-being of patients with multiple sclerosis.