BDNF and complex regional pain syndrome: BDNF serum levels were higher in CRPS subjects and remained unchanged after L4-DRGSTIM (HC: 31,424,18 ± 9326,80 pg/ml versus pre-DRGSTIM: 39,425.40 ± 10,234.85 pg/ml versus post-DRGSTIM: 38,699.21 ± 8054.56 pg/ml).