Participants in this study will be randomly assigned to receive SAM-e, escitalopram, or placebo for 12 weeks. Some participants may choose to extend treatment for an additional 12 weeks (for a total of 24 weeks on study medication). Participants will have study visits at entry and Weeks 2, 4, 8, and 12. Study visits will include neurological evaluation, psychiatric evaluation, blood tests, and quality of life questionnaires. A telephone interview will be conducted at Week 10.