BDNF and depressive symptom measurement: Haas et al. [56] discovered no significant relationship between plasma BDNF level and VAS (r = -0.12, p-value = 0.50), number of tender points (r = -0.02, p-value = 0.89), or Hamilton Depression (HAM-D) score (r = -0.14, p-value = 0.44).