TNF and complex regional pain syndrome: Pro-inflammatory cytokines, including interleukin -1β, interleukin-6 and tumor necrosis factor-alpha, play an important role in the relationship of diabetes mellitus and CRPS I. Skin biopsy results show that the expression of pro-inflammatory cytokines was significantly higher in the upper extremities of CRPS-affected patients than in those of the unaffected patients [36, 37].