Euthanasia and Persons with Dementia: An Ethical Dilemma

According to the Belgian euthanasia law, people with dementia who want to choose their end of life can only decide for euthanasia, in an early state of dementia, still autonomous, disposing of their full mental capacities. This way, one can loose precious quality lifetime.
Are advance directives possible for persons with dementia?
Ronald Dworkin differentiates between ‘experiential interests’ (actual pleasures) and ‘critical interests’ (values giving life as a whole meaning), and builds up an argumentation in favour of advance directives for dementia.
In contrast, Rebecca Dresser focalizes on the ‘experiential interests’ of a person with dementia, being another person then he was in the past, and as a consequence advance directives are useless.
From Agnieszka Jaworska we learn that persons with dementia have, with proper respectfull care, much longer then their cognitive capacities, disposition of their values.
By taking the ‘ability to value’ (Jaworska) in account as an essential part of an autonomous choice, person’s with dementia who want to choose for euthanasia can do this in a more advanced phase of the disease and gain a longer quality lifetime. Going one step further, as long as the values of the patient are congruent with his advanced directives, then the latter might become acceptable.