[Competency: general principles and applicability in dementia].

INTRODUCTION Competency means the capacity to make responsible and balanced decisions. This may be performed in clinical settings (decision-making abilities on treatment or risky diagnostic procedures) and also in daily-life activities (financial matters, nursing home admittance, contracts, etc.). Competency is linked to the ethical principle of autonomy and to a horizontal doctor-patient interaction, far from ancient paternalistic relationships. It is contemplated in the Spanish law as the patient's right to be informed and to make free choices, particularly in cases of dementia. DEVELOPMENT The competency that we assess is the so-called natural or working capacity. It is specific for an action or task. The level of required capacity depends on the decision: higher for critical ones, lower for low-risk decisions. The assessment process requires noting the patient's capacity to understand, analyse, self-refer and apply the information. There are some guides available that may be useful in competency assessments, but nevertheless the final statement must be defined by the physician in charge of the patient and clinical judgement. Capacity is directly related to the level of cognitive deterioration. Nevertheless, specific cognitive tests like MMSE (mini-mental) have a low predictive value. The loss of competency is more associated with the so-called legal standards of incapacity (LS). These encompass a five steps range (LS1-LS5), which may detect the incapacity from the mild levels of dementia. The cortical functions that are the best predictors of incapacity are language and executive dysfunctions. These explain the incapacity in cases of Alzheimer's and Parkinson's disease, and have been studied more. CONCLUSIONS Incapacity is common and it influences the clinical decision-making process. We must be particularly cautious with clinical trials of dementia. It also involves other areas of daily life, particularly financially related ones, where limitations are present from the mild cognitive impairment level. The neurological community has already produced specific and invaluable documents like the one from Sitges, although in our opinion this community has to increase its awareness, and also its involvement as much in the clinical as in the research sides of this field.