[1] New England Ctr Headache, Stamford, CT USA
[2] Thomas Jefferson Univ, Jefferson Headache Ctr, Philadelphia, PA 19107 USA
[3] Nashville Neurosci Grp, Nashville, TN USA
[4] Merck & Co Inc, Dept Clin Neurosci, Blue Bell, PA USA
[5] Merck & Co Inc, Dept Clin Neurosci, Brussels, Belgium