Evaluation of symptom heterogeneity in neuropathic pain using assessments of sensory functions.

Classification of neuropathic pain has been based on disease entities, anatomical localization, or histological observations. Over the past decade, there has been an explosion in our understanding of the basic mechanisms of neuropathic pain. The exciting advances in basic science are paralleled by the recognition from clinical investigations that neuropathic pain is not a monolithic entity, but instead presents as a composite of pain and other sensory symptoms. Attempts are under way to supplement the traditional classification with a classification that links pain and sensory symptoms with neurobiological mechanisms. This mechanism- or symptom-based classification takes both negative and positive sensory symptoms into account. By using a battery of several standardized quantitative sensory tests, the characteristic profile of sensory symptoms can be elucidated in each patient. Moreover, in questionnaires the verbal descriptors can depict the quality and intensity of the individual pain. The approach of classifying and subgrouping patients with neuropathic pain on the basis of symptoms or signs opens up new possibilities for stratifying patients in clinical trials. First, in clinical proof-of-concept trials the study population can be enriched prospectively on the basis of entry criteria defined a priori. This enrichment with patients who potentially require a specific treatment should increase the likelihood for positive trial outcomes. Second, in clinical practice it becomes possible to establish an individualized therapy--that is, to identify the particular patients who require a specific treatment option.