Among patients diagnosed with Alzheimer's disease (AD), the percentage in the severe stage ranges from 28%  to 33%  to a maximum of 50% . In institutionalized patients, prevalence is higher, with an estimated 75% of patients with severe AD . Cognitive impairment is well defined when it is considered "mild" and "moderate", however, there is a lack of precision and consensus when cognitive impairment is considered "severe", “profound”, or "advanced". The reference manual DSM (Diagnostic and Statistical Manual of Mental Disorders) contains too simple a definition: DSM-IV-TR  describes advanced dementia as a "final period, during which there is personal disorientation and a complete loss of self-care. In more advanced stages of dementia, memory impairment is so severe that the person forgets his occupation, studies, date of birth, family composition, and sometimes even his name. In these stages, subjects may suffer mutism or have a speech pattern characterized by echolalia, and unable to recognize his family or even his own image in the mirror". DSM-V  is shorter, describing patients with AD at an advanced stage as "become mute and bedridden”. The ICD-10  defines the degree of memory loss in this phase as "characterized by the complete inability to retain new information, and only remaining fragments of previously learned information. The subject cannot recognize even close relatives, and there is a decline in all cognitive functions characterized by an absence, or virtual absence, of intelligible thought”. If we had to put cut off points in cognitive assessment scales, we would find that some authors have defined severe AD as a score less than or equal to 95 points in the Dementia Rating Scale . In other studies, it was considered to be severe AD when a Mini-Mental State Examination (MMSE)  under 10  or 12 points  was obtained. On many occasions, the patient's functional status was used as an indicator to classify the stage of dementia. This is because, usually, at this stage the patient requires constant supervision, has lost all Instrumental Activities of Daily Living and most or all of the Basic Activities of Daily Living. This functional situation corresponds to the values of the Global Deterioration Scale  and the Functional Assessment Staging  greater than or equal to 6, and the Clinical Dementia Rating Scale  with level 3 . One of the advantages of functional scales regarding cognitive scales is that the level of education, age, sex, country of origin, and educational level have less influence when applying these scales. So it seems more appropriate to use functional scales to determine the AD as severe, but a number of factors must be taken into account which preclude the exclusive use of functional scales :
They can be affected by other diseases, primarily psychiatric, such as depression or anxiety.
They can be influenced by the overprotection of the caregiver.
They can be influenced by the quality of the relationship between the informant and patient.
It is difficult to accommodate variability in the progression of dementia in different cognitive and behavioral domains.
They do not provide enough information about the cognitive status of the patient to facilitate an adequate intervention plan with the means to improve the problems caused by this deterioration. It has been shown that there is a correlation between global measures of functional status in patients with severe AD, as measured by the Alzheimer's Disease Cooperative Study Activities of Daily Living , and the measured cognitive status with the Severe Impairment Battery  and the MMSE , indicating that the execution of these general indices of cognitive functioning predict functional capacities. Therefore, it is advisable to use both types of scales, functional and cognitive, if we want to assess whether a patient has progressed to the severe stage of the disease.
What criteria or cut off point do you use in your clinical practice to define severe AD?
For the diagnosis of severe AD: Do you think we should use more cognitive or functional scales?
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