A more pessimistic life orientation is associated with experimental inducibility of a neuropathy-like pain pattern in healthy individuals
The clinical pattern of neuropathic pain, diagnosed using the quantitative sensory testing (QST) battery (German Research Network on Neuropathic Pain), could be partly mimicked in healthy volunteers after topical capsaicin application. However, similar to clinical neuropathic pain that develops in only a subgroup of patients who have a neurologic lesion, this attempt to mimick a neuropathic pain pattern succeeded only in a small fraction (18%) of healthy individuals. In the present assessment, we pursued the hypothesis that the inducible subgroup differed from the other healthy participants with respect to their psychological phenotype. Therefore, in an observational study, participants were assessed using a comprehensive set of psychological variables comprising general psychological and pain-related cognitive-emotional mechanisms. The sum scores of the questionnaires were significantly linearly correlated with each other. Principal component analysis indicated that a major source of variance (46%) could be attributed to dispositional optimism examined via the Life Orientation Test (LOT). The LOT score significantly differed between the groups of participants, either those in whom a neuropathy-like pattern of pain assessed via QST could be partly (50-60% of the 11 QST parameters) induced (n = 20) or not (n = 90; P = .0375). It emerged again as the main selection criterion in a classification and regression tree predicting a participant's group assignment (inducible neuropathy-like QST pattern versus noninducible neuropathy-like QST pattern) at a cross-validated accuracy of 95.5 ± 2.1%. Thus, the few participants in a random sample of healthy volunteers who, after topical capsaicin application, partly resemble (to a degree of about 60%) the clinical pattern of neuropathic pain in the QST test battery, are preselectable on the basis of psychological factors, with a particular emphasis on pessimistic life attitudes. Perspective In a small fraction of 18% of healthy volunteers, topical capsaicin application resulted in a neuropathy-like pattern in 50 to 60% of the components of a clinical test battery. These individuals displayed a more pessimistic life attitude as assessed by means of the LOT.