The Managing Editor of the AMA Manual of Style suggests formatting UpToDate topics the same way that you would cite a website:
Pasternak B. Carvedilol vs metoprolol succinate and risk of mortality in patients with heart failure: national cohort study. Paper presented at: European Society of Cardiology Congress; August 31, 2014; Barcelona, Spain.
Nevidomskyte D, Meissner MH, Tran N, Murray S, Farrokhi E. Influence of gender on abdominal aortic aneurysm repair in the community. Poster presented at: Vascular Annual Meeting; June 5-7, 2014; Boston, MA.