[Concept of resistant depression].

Resistant depressions can be defined as those depressions in which the spontaneous course is not influenced by therapeutic measures. Resistance to treatment is not an exceptional phenomenon, as it occurs in 15 to 30% of cases; the imprecision of this evaluation is essentially due to the losse definition of resistant depression and the various ways in which it is interpreted. For example, the concept of a "therapeutic measure" varies between the epidemiological approach, according to which it implies any form of therapy designed to treat the depression, and the clinical psychiatric approach, which reserves this term for the administration of rational antidepressant treatment over a sufficient period of time. The concept of "lack of influence" (or failure) of a therapeutic measure is also open to discussion: in the absence of absolute criteria for the characterisation of the patient's state of health, the definition of resistant depression can vary considerably. The study of factors of resistance to treatments allows therapeutic factors to be distinguished from clinical factors. In practice, inadequate treatment is the principal cause of "resistance". This inadequacy can be due to a number of reasons: poor choice of treatment, inappropriate dosage, insufficient duration of treatment, rejection of certain tried treatments (electroshock, MAOI), etc. Some cases of depression are found to be more frequently resistant, whichever treatment is administered.(ABSTRACT TRUNCATED AT 250 WORDS)