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The Different Kinds of Cognitive Decline

Updated: Nov 14, 2022

Cognitive decline is a very broad category, referring to a decline in one or more cognitive domains. These can include but are not limited to learning and memory, attention and concentration, language, executive function, and processing speed. Cognitive decline can vary from mild to moderate to severe. Some patients with a diagnosis of mild cognitive impairment (MCI) may never progress to develop dementia. However, in some cases, patients can progress to experiencing frank dementia, which is a broad term referring to the loss of one or more cognitive domains severe enough to interfere with daily living.


Alzheimer’s Disease: most people are familiar with Alzheimer’s Dementia as one category, as this is the most common type of dementia, accounting for 60-80% of cases of dementia. Age at onset is typically over 65, however, there are cases of early-onset as well. Most commonly, symptoms begin with a decline in short-term memory and an inability to recall recently learned information. However, other symptoms can occur, including deficits in language, processing speed, and other domains as well. Oftentimes, patients themselves are unaware of a decline, yet deficits are perceived by family members or friends. While there are some less common inherited forms of Alzheimer’s Disease, most cases are not inherited. The disease is known to be associated with a build-up of 2 types of proteins which ultimately lead to death and destruction of nerve cells:

  1. Beta-amyloid: this protein accumulates into plaques in the brain. This is a protein that is present in smaller amounts in healthy brains and actually serves to have some anti-microbial effects. However, in those with Alzheimer’s disease, amyloid excessively accumulates and contributes to pathology.

  2. Tau protein: this is a protein that also accumulates and forms what is referred to as Neurofibrillary Tangles

Vascular Dementia: Considered to be the second most common form of dementia, this accounts for 5-10% of cases. Often thought of as having a step-wise progression, this form of dementia results after repeated insults that deprive blood flow to different regions of the brain. Symptoms of memory loss and cognitive impairment can occur acutely after a large stroke or after an accumulation of smaller strokes affecting very tiny blood vessels in the brain. Depending on the brain regions involved, presentations can vary and may involve memory loss, difficulty with speech, confusion, and disorientation.

Lewy Body Dementia: This is thought to be the third most common type of dementia. A certain protein deposit called alpha-synuclein and referred to as “Lewy bodies” accumulate in regions involved not only in memory but also movement. For this reason, issues with motor control similar to those seen in Parkinson’s disease may develop (such as slower movements, postural instability, tremors, and muscle rigidity). However, motor issues are typically not the first symptom. Cognitive issues are similar to those experienced in Alzheimer’s disease. One of the hallmarks and often one of the first symptoms can be visual hallucinations (seeing people, animals, or objects that are not really there). Fluctuations in attention or “on/off phenomenon” can also be giveaways for Lewy Body Dementia. Periods of alertness will fluctuate with periods of drowsiness and lack of attention. Additionally, rapid eye movement (REM) sleep behavior disorders may be an issue that manifests as acting out your dreams.

Parkinson’s Disease-associated dementia: Dementia can develop in those diagnosed with Parkinson’s Disease, although motor symptoms must always precede any cognitive decline. Parkinson’s Disease is predominantly a movement disorder, affecting 2% of those over the age of 65 and involves a combination of tremors, rigid muscles, postural instability, and slow movements. Lewy bodies also accumulate in Parkinson’s Disease. It is estimated that between 50-80% of patients with Parkinson’s Disease will eventually experience dementia. It is also estimated that the average time of onset of dementia is about 10 years after the diagnosis of Parkinson’s disease. Dementia that ensues is similar clinically to that of Alzheimer’s Dementia and includes changes in memory and concentration, altered judgment, and deficits in visual-spatial domains.

Chronic Traumatic Encephalopathy (CTE): While there is no evidence that a single episode of mild traumatic brain injury (TBI) increases your dementia risk, several studies support that TBI is a significant risk factor for cognitive decline, and also acerates the age at onset of the decline. While TBI is a known risk factor for Alzheimer’s type dementia, there is also a risk for CTE. CTE is actually understood as a chronic neurodegenerative disease, associated with a build-up of a protein called tau. Tau protein starts to become misshapen and sets off a chain reaction in which more tau begins to build up in the brain which ultimately causes neurons to die off. CTE is known to be associated with a triad of symptoms, which include aggression, depression, and dementia. Originally recognized in boxers and referred to as “dementia pugilistica”, we now recognize it as having a higher incidence in several types of athletes as well as military veterans.

Other less common types of dementia: There are a few other less common, specific types of dementia, which are typically recognized by a specially trained neurologist. These include Fronto-temporal dementia, Progressive Supranuclear Palsy, Normal Pressure Hydrocephalus, and Posterior Cortical Atrophy.

Reversible causes of cognitive decline not to be missed: While Alzheimer’s Disease is the most readily recognized form of dementia by most physicians, among those not to be missed are reversible causes of dementia. Red flags include younger than expected age at onset of symptoms, rapid and unexplained decline, and fluctuations in symptoms.

  1. Nutritional causes include several B vitamins, including B12 (most well-known), B1 (thiamine), B6, and B9 (folate).

  2. Metabolic causes include those related to thyroid disorders, metabolic syndrome, and diabetes.

  3. Toxic causes including certain medications, chronic alcohol use, some heavy metals like mercury and lead as well as some environmental toxins such as chronic pesticide exposure.

    1. Medications known to precipitate cognitive decline include narcotics, benzodiazepines, and anticholinergic medications.

  4. Inflammatory causes such as autoimmune encephalitis.

  5. Epileptic causes – transient epileptic amnesia often occurs after seizures. With more frequent seizures, patients can also experience memory impairment even in between seizure episodes.

  6. Structural causes such as from chronic bleeding, a tumor, or a condition known as Normal Pressure Hydrocephalus (NPH).

Make sure to keep an eye out for next week's blog! We'll chat about what signs and symptoms of cognitive decline you can watch for in yourself and your loved ones.


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