Although the exact time frame varies, preclinical Alzheimer's can last for more than 20 years. Mild to moderate Alzheimer's can range from two to 10 years, while the severe stage typically lasts for no more than five years, according to the Alzheimer's Association.
Preclinical Alzheimer's disease is the earliest stage and does not involve any noticeable symptoms, reports Mayo Clinic. This stage involves subtle changes to the brain and used to be impossible to detect. However, there is a test that can show the presence of amyloid beta, which may be an early sign of the disease.
Mild and moderate Alzheimer's disease typically involves mild cognitive impairment, notes the Alzheimer's Association. In the earliest stages, the person may still be able to live independently with minimal help. However, he may struggle with more complicated tasks, such as balancing checkbooks or paying bills. He may also struggle to stay organized or remember people's names. The moderate stage involves a progression of these symptoms, often to the point where the patient needs a caregiver.
As of 2015, there are some medications which may be able to slow the progression of Alzheimer's disease in early stages, reports Healthline. However, these medications may only be treating the symptoms and may not add any actual time to the person's life. These can prolong the person's ability to live independently and have a higher quality of life during the earlier stages of the disease.