Mild Cognitive Impairment Due to Alzheimer's Disease: Understanding The Stages

Advances in biomarkers, both traditional and digital, have shifted the way we view Alzheimer’s disease. There is increased recognition that Alzheimer’s disease should be viewed as a multifaceted process that moves along a continuum. Throughout this continuum, the presence and manifestation of Alzheimer’s disease vary depending on the stage of the disease.

In this article, we provide a high-level overview of the stages in the Alzheimer's disease continuum, with a focus on Mild Cognitive Impairment (MCI) due to Alzheimer’s disease.

The Alzheimer's Disease Continuum: Understanding the Stages

The Alzheimer's disease continuum consists of five stages: 

1. Preclinical Alzheimer’s disease
2. Mild Cognitive Impairment due to Alzheimer’s disease
3. Mild dementia due to Alzheimer's disease
4. Moderate dementia due to Alzheimer's disease
5. Severe dementia due to Alzheimer's disease

Preclinical Alzheimer’s Disease

Alzheimer's disease and the consequent changes in the brain begin long before symptoms arise. Preclinical Alzheimer’s disease is the first phase of the Alzheimer’s disease continuum and is a newly defined stage commonly referred to as the “silent” stage of Alzheimer’s disease because no clinical symptoms are present. In the majority of cases, individuals with preclinical Alzheimer’s disease will not notice any symptoms, nor will their friends and family. The preclinical stage can last years, possibly even decades. 

Preclinical Alzheimer's disease begins when the first neuropathologic brain lesions show up in the brain and ends when the first recognizable clinical symptoms begin. The first lesions to appear in the brain are beta-amyloid plaques, a distinct pathology of Alzheimer's. Beta-amyloid proteins begin to collect in the brains of those with Alzheimer's disease as early as 20 years before symptom onset.

Mild Cognitive Impairment Due to Alzheimer’s Disease

Mild Cognitive Impairment causes changes in cognitive function significant enough to be noticed by friends or family, but not significant enough to affect daily functioning. Mild Cognitive Impairment can be caused by a variety of conditions, including neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease and other conditions such as depression, thyroid problems, liver or kidney problems, and sleep disorders, among others.

Mild Cognitive Impairment is typically classified based on which cognitive abilities are affected:

• Amnestic Mild Cognitive Impairment (aMCI): In patients with aMCI, memory impairment is significant while other cognitive functions remain intact. aMCI is associated with a higher risk of conversion to Alzheimer’s disease.
• Nonamnestic Mild Cognitive Impairment (naMCI): In patients with naMCI, memory remains intact while one or more other cognitive domains are impaired significantly.

The standard criteria for Mild Cognitive Impairment are as follows:

• A concern about changes in cognitive abilities
• Impairment in one or more cognitive domains (more than expected given the patient’s age and education level)
• The preservation of independence in functional abilities
• No significant impairment in social or occupational functioning (not demented)

To know with certainty that Mild Cognitive Impairment is caused by or is due to Alzheimer’s disease, Alzheimer’s pathology must also be present in addition to meeting the above criteria.

Mild Cognitive Impairment due to Alzheimer’s disease, often referred to as the prodromal stage of Alzheimer’s disease, is the second stage in the continuum. Individuals with Mild Cognitive Impairment due to Alzheimer’s disease have minor changes to their memory, thinking, and other cognitive abilities. This decline in cognitive abilities is typically not severe enough to interfere with patients’ Activities of Daily Living (ADLs) or daily functioning, meaning the changes are not significant enough to affect work, family, or personal relationships.

Symptoms of Mild Cognitive Impairment due to Alzheimer’s disease include:

• Losing or misplacing things often.
• Forgetting important events, such as social engagements and appointments.
• Losing your train of thought or having difficulty coming up with the right word.
• Difficulty with decision-making or planning.
• Changes in judgment and impulse control.
• Changes in mood (e.g., anxiety, depression, apathy, and irritability).

Mild Dementia due to Alzheimer’s Disease

Individuals with mild dementia due to Alzheimer’s may still be able to live and complete ADLs independently, but have experience symptoms such as:

• Short-term memory loss.
• Difficulty planning or performing familiar tasks.
• Changes in speech (e.g., difficulty recalling words or finding the right word to use, pausing while speaking, struggling to finish a sentence, and having difficulty organizing or expressing thoughts).
• Changes in mood or personality. 
• Poor orientation (e.g., forgetting your location or how you ended up there and getting lost in familiar places).
• Changes in visual perception (e.g., having difficulty judging distances and experiencing challenges while driving).
• Money management issues.

Moderate Dementia Due to Alzheimer’s Disease

Typically, there are similar symptoms in this stage to the previous stage, but the symptoms become more pronounced. In addition to cognitive changes, they may also experience function changes, such as issues with fine motor coordination and changes in gait. Individuals with moderate dementia due to Alzheimer’s disease may have difficulty completing normal ADLs, such as eating, bathing, and dressing, and may require assisted living. 

Severe Dementia Due to Alzheimer’s Disease

Individuals with severe dementia due to Alzheimer’s disease will require assistance with most normal activities. In this stage, symptoms typically include:

• Difficulties with communicating coherently.
• Inability to independently complete activities such as eating, bathing, dressing, and toileting. 
• Being unaware of recent experiences or your surroundings.
• Loss of physical abilities (e.g., walking, sitting, and eating).
• Loss of bladder or bowel control.
• Stiffness and rigidity in the muscles.