Methodological issues raised by clinical trials on dysthymia: assessment instruments and response criteria.

Dysthymia clinical trials raise several methodological issues. The validity of the concept remains a matter of concern, as does the need for specific instruments, the difficulties in assessment of change and long-term assessments. Diagnostic criteria for inclusion should be used in a polydiagnostic approach. This paper summarises the main assessment tools and diagnostic criteria used in clinical trials on dysthymia. Severity criterion for inclusion could be a Hamilton Depression Rating Scale score (HAMD-17) between 13 and 17. The main response criteria should be a decrease of at least 50% of the total score on this scale and a final score under a predetermined limit. However, other response criteria may be useful: depression self-ratings, global assessments, general psychopathology assessments, personality and defense mechanisms, quality of life, psychosocial and functional impairment, diagnostic criteria (presence or absence) and side-effect assessment.