Botulinum toxin type a for the prophylaxis of chronic daily headache: subgroup analysis of patients not receiving other prophylactic medications: a randomized double-blind, placebo-controlled study - Dodick, DW; Mauskop, A; Elkind, AH; DeGryse, R; Brin, MF; Silberstein, SD; BOTOX CDH Study Group (Headache, 2005)