NGF and Headache: A higher frequency of headache days correlated positively with higher levels of serum NGF (ρ = 0.476; p-value<0.001) and PGE2 (ρ = 0.286; p-value=0.028), while serum VEGF and BDNF levels did not correlate significantly with number of headache days/month in migraine patients (BDNF: ρ = 0.037 and p-value=0.778; VEGF: ρ= -0.025 and p-value=0.850).