What is Dementia
Dementia is defined as a set of brain disorders that result in general cognitive decline. Dementia affects cognitive functions like memory, speech, judgment, reasoning, and visual perception. People suffering from dementia cannot live their life properly. They are dependent on others to perform even the most basic tasks. Dementia is the most common cause of disability among the older population of the world. The general symptoms of dementia can vary depending upon the cause of dementia. Life expectancy has increased in developed countries, and it continues to increase in underdeveloped countries due to better health measures such as vaccinations, availability of antibiotics, a healthy diet, and a clean environment. This increase in life expectancy has exposed the world population to age-related illnesses.
Forms of Dementia
Dementia is the most devastating of these age-related illnesses. It deprives people of their independence and makes the final stages of their life miserable. As the population ages, dementia will continue to have a greater impact on socioeconomic conditions. In this article, we have elaborated on the epidemiology, socioeconomic impacts, symptoms, and pathophysiology of major types of dementia.
Alzheimer’s Disease Alzheimer’s Disease (AD) is the major form of dementia. The pathological processes responsible for AD begin decades before the onset of symptoms. The symptoms of AD include the most typical symptoms usually associated with dementia. These symptoms include a decline in short-term memory, judgment, and decision-making ability. So far, the best explanation of molecular processes leading to AD is given by the amyloid cascade hypothesis. Beta-amyloid (Aβ) produced from amyloid precursor protein (APP) accumulates within the neurons. Tau protein is also involved in AD. AD is considered a secondary tauopathy. The combined toxic effect of Aβ and hyperphosphorylated tau damages neurons and synapses in the brain. Currently, there is no disease-modifying treatment for AD; however, the symptoms can be managed individually using different drugs. Cholinesterase inhibitors are typically used for symptomatic management of AD and function to decrease the breakdown of acetylcholine. As a consequence, the relative increase in acetylcholine results in increased communication between nerve cells, which in turn, may temporarily improve or stabilize the symptoms of dementia.
Vascular dementia (VD) occurs due to diminished blood supply to the brain. Stroke is the most common cause of this impaired blood supply to the brain. Symptoms of VD can vary depending on which part of the brain is receiving less than normal blood. Usually, frontal and temporal lobes are affected; therefore, the most common symptoms of VD are a decline in reasoning and decision-making abilities. The risk factors of VD include general risk factors of cardiovascular diseases.
Lewy Body Dementia
Lewy body dementia (LBD) is an umbrella term that includes dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD). DLB is characterized by the presence of Lewy bodies in the limbic system, brain stem, and neocortical parts of the brain. Lewy bodies are composed of many proteins. α-Synuclein is the major protein in Lewy bodies. α-Synuclein is a small protein of only 140 amino acids. Visual hallucinations are strong in DLB and parkinsonian symptoms appear later in the disease. There is no disease-modifying treatment of DLB. The symptoms can be managed through appropriate drugs.
Parkinson’s Disease Dementia
Parkinson’s Disease Dementia (PDD) is characterized by the presence of early motor symptoms. Dementia symptoms appear later in the disease. α-Synuclein is also the major protein involved in the pathophysiology of PDD. Other proteins such as ubiquitin are also involved. Braak's hypothesis gives the best explanation of the origin and spread of PDD pathology. α-Synuclein pathology first originates in the peripheral nervous system and olfactory bulb and then propagates to substantia nigra.
Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by the degradation of the frontal and temporal lobes. A variety of proteins are involved in the pathophysiology of FTD. These proteins include Tau and TAR DNA-binding protein 43 (TDP-43). In the clinical setting, two major variants of FTD have been identified. These are Behavioral Frontotemporal (bvFTD) and Primary Progressive Aphasia (PPA). Emotional instability, inhibition, obsessive and compulsive behaviors, lack of motivation, change in eating habits, and lack of empathy are the major symptoms of FTD.
Mixed dementia is the coexistence of different types of pathology in an individual. The coexisting pathologies often potentiate each other. AD and VD are most common in mixed dementia. Mixed dementia patients show symptoms of both AD and VD. These overlapping symptoms pose a challenge in identifying the correct diagnosis. Treatment of mixed dementia involves the management of contributing dementias separately.
Written By: Numair Arshad & Lawrence D. Jones, Ph.D.