Alzheimer’s Disease

Disease Progression

  • In Alzheimer’s disease (AD), the brain areas first affected - the hippocampus, entorhinal cortex and portions of the frontal lobe - perform the function of recording and retrieving recently learned information or recently experienced events. It is known that the changes in the brain due to AD start as early as 30 years prior to the first symptoms of memory loss appear. This 30-year period is called the asymptomatic stage of AD, and is followed by the stage called mild cognitive impairment (MCI), which lasts approximately seven years.

    During the MCI of AD, the primary symptoms are difficulty recalling recently learned knowledge or recent events and difficulty doing complex tasks that require sustained concentration and use of newly learned information. Recent knowledge or events that have occurred within the last two weeks are the most difficult to recall because the hippocampus stores newly learned information for this period of time, then “erases” the recording. Memories that are more than a few weeks old are retrieved from the cortex and do not require the hippocampus, which is why persons in the MCI stage of AD can recall events that occurred a long time ago without difficulty but may ask the same question within a few minutes.

    After this seven-year period of MCI, the dementia stage of AD begins, which lasts approximately seven more years, such that the symptomatic stages of AD last approximately 14 years. During the dementia stage of AD, well-learned activities of life are affected, including managing finances, driving, shopping, cooking, running a household, and performing well-learned hobbies. After these abilities are affected, more rudimentary abilities become impaired, including dressing, bathing, using the toilet and controlling bowel and bladder. The final stages of AD involve the loss of language, followed by loss of ability to walk, sit up straight, smile and then hold one's head up.

    The dementia stage AD is further divided into mild, moderate and severe stages. Unfortunately, “mild dementia” does not necessarily mean “mild.”

    Although the clinical course of AD is 14 years, most patients are first diagnosed after 9 to 11 years of symptoms, at which point they are mild to moderately demented [reference]. In routine medical practices, 1 out of 4 persons over 65 years old has MCI or mild dementia [reference], but among those affected, only 10% have been detected and diagnosed [reference]. This means that casual observation does not detect cognitively impaired and demented patients 90% of the time. Early detection can only be achieved by incorporating a sensitive memory or cognitive assessment into the routine clinical care for persons over 65 years old or even younger if the person has higher risks for AD.