Status of immune mediators in painful neuropathies.

Peripheral neuropathies of identical etiology can be painful or painless. The reason for this difference in clinical presentation is as yet unknown; however, immune mediators, particularly cytokines, may play a role. Cytokines are proteins that are produced by immune and nonimmune cells and are categorized as pro- and anti-inflammatory. The role of cytokines in the induction and maintenance of pain has been well established in animal models. Proinflammatory cytokines are mostly algesic, whereas anti-inflammatory cytokines have analgesic properties. Clinical research also gives evidence for the involvement of cytokines in painful and painless neuropathies. A proinflammatory cytokine profile seems to be associated with pain in peripheral neuropathies of different etiologies and in other painful disorders such as the complex regional pain syndrome. Specifically, an imbalance between pro- and anti-inflammatory cytokines may contribute to pain generation. A better understanding of the underlying pathophysiology may open new opportunities for the treatment of pain.