[1] Walter Reed Army Med Ctr, Dept Surg, Washington, DC 20307 USA
[2] Harvard Univ, Sch Med, Beth Israel Deaconess Med Ctr, Dept Anesthesiol & Crit Care,Pain Management Div, Boston, MA USA
[3] Beth Israel Deaconess Med Ctr, Dept Neurol, Boston, MA 02215 USA
[4] Johns Hopkins Univ, Sch Med, Dept Anesthesiol & Crit Care Med, Pain Management Div, Baltimore, MD 21205 USA