Neuropathic pain: the clinical syndrome revisited.

Neuropathic pains associated with an injury of the peripheral or central nervous system are among the most difficult to treat. One of the reasons for the therapeutic difficulties in these patients is that the pharmacological treatments are used in a uniform fashion whatever the clinical picture, while these syndromes are in fact highly heterogenous. The patients can express various combinations of painful symptoms--spontaneous (continuous and/or paroxysmal) and evoked (allodynia and/or hyperalgesia). Recent pharmacological studies have shown that current treatments of these pains do not induce global and uniform analgesic effects but rather act preferentially or selectively on some of their components. Such data emphasize the necessity of a thorough evaluation of patients presenting with neuropathic pains, notably by using quantitative sensory testing. Following recent advances in the understanding of the pathophysiological mechanisms underlying these painful syndromes, through experimental studies in animals, a "mechanism-based" classification and treatment of neuropathic pains can be envisaged. The main goal for clinicians is to propose new methods and strategies for identifying pathophysiological mechanisms in patients in order to validate such an approach in the clinical context.