Furthermore, some data presented in these studies are contradictory; for example, while one study showed no difference in blood lymphocyte populations (i.e., (cytotoxic) CD8+ T-cells, CD4+ T-cells, B-cells, and natural killer (NK) cells) between CRPS patients and healthy controls, another study found that CRPS was associated with a significant reduction in the number of CD8+ T-cells [6, 20]. Here, CD4 is linked to complex regional pain syndrome.