[Assessing disability in chronic pain patients.].

Despite its importance for chronic pain diseases, pain-related disability is a poorly defined concept with theoretical deficits. The distinction between impairment, disability, and handicap proposed by the WHO is an important contribution to clarification of the disability construct. With reference to four criteria (underlying disability construct, degree of behaviour generalization, assessment mode, scope) different assessment procedures of pain-related disability are presented and the advantages and disadvantages of each are discussed. A multidimensional approach to pain-related disability is advocated. Diagnostic information yielded by different assessment procedures should be viewed as complementary rather than as exclusive data sources. A German version of a self-report instrument (Pain Disability Index) that assesses disability in chronic pain patients is presented. The results from four data sets concerning different aspects of reliability and validity confirm the good psychometric properties of the instrument. The instrument can be used in chronic pain research as well as in clinical contexts. It is recommended that subjective disability data be complemented by behavioral observation and additional data sources (e.g. assessment of disability by the spouse/partner).