formed by hyperphosphorylated tau proteins, are two well-established pathological hallmarks of ad. amyloid causes inflammation around the senile plaques of the brain, and too much build up of this inflammation leads to changes in the brain that cannot be controlled, leading to the symptoms of alzheimer's. vascular main article: vascular dementia vascular dementia accounts for at least 20% of dementia cases, making it the second most common type. it is caused by disease or injury affecting the blood supply to the brain, typically involving a series of mini-strokes. the symptoms of this dementia depend on where in the brain the strokes occurred and whether the blood vessels affected were large or small. repeated injury can cause progressive dementia over time, while a single injury located in an area critical for cognition such as the hippocampus, or thalamus, can lead to sudden cognitive decline. elements of vascular dementia may be present in all other forms of dementia. brain scans may show evidence of multiple strokes of different sizes in various locations. people with vascular dementia tend to have risk factors for disease of the blood vessels, such as tobacco use, high blood pressure, atrial fibrillation, high cholesterol, diabetes, or other signs of vascular disease such as a previous heart attack or angina. lewy bodies the prodromal symptoms of dementia with lewy bodies (dlb) include mild cognitive impairment, and delirium onset. the symptoms of dlb are more frequent, more severe, and earlier presenting than in the other dementia subtypes. dementia with lewy bodies has the primary symptoms of fluctuating cognition, alertness or attention; rem sleep behavior disorder (rbd); one or more of the main features of parkinsonism, not due to medication or stroke; and repeated visual hallucinations. the visual hallucinations in dlb are generally vivid hallucinations of people or animals and they often occur when someone is about to fall asleep or wake up. other prominent symptoms include problems with planning (executive function) and difficulty with visual-spatial function, and disruption in autonomic bodily functions. abnormal sleep behaviors may begin before cognitive decline is observed and are a core feature of dlb. rbd is diagnosed either by sleep study recording or, when sleep studies cannot be performed, by medical history and validated questionnaires. parkinson's disease parkinson's disease is a lewy body disease that often progresses to parkinson's disease dementia following a period of dementia-free parkinson's disease. frontotemporal main article: frontotemporal dementia frontotemporal dementias (ftds) are characterized by drastic personality changes and language difficulties. in all ftds, the person has a relatively early social withdrawal and early lack of insight. memory problems are not a main feature. there are six main types of ftd. the first has major symptoms in personality and behavior. this is called behavioral variant ftd (bv-ftd) and is the most common. the hallmark feature of bv-ftd is impulsive behavior, and this can be detected in pre-dementia states. in bv-ftd, the person shows a change in personal hygiene, becomes rigid in their thinking, and rarely acknowledges problems; they are socially withdrawn, and often have a drastic increase in appetite. they may become socially inappropriate. for example, they may make inappropriate sexual comments, or may begin using pornography openly. one of the most common signs is apathy, or not caring about anything. apathy, however, is a common symptom in many dementias. two types of ftd feature aphasia (language problems) as the main symptom. one type is called semantic variant primary progressive aphasia (sv-ppa). the main feature of this is the loss of the meaning of words. it may begin with difficulty naming things. the person eventually may lose the meaning of objects as well. for example, a drawing of a bird, dog, and an airplane in someone with ftd may all appear almost the same. in a classic test for this, a patient is shown a picture of a pyramid and below it a picture of both a palm tree and a pine tree. the person is asked to say which one goes best with the pyramid. in sv-ppa the person cannot answer that question. the other type is called non-fluent agrammatic variant primary progressive aphasia (nfa-ppa). this is mainly a problem with producing speech. they have trouble finding the right words, but mostly they have a difficulty coordinating the muscles they need to speak. eventually, someone with nfa-ppa only uses one-syllable words or may become totally mute. a frontotemporal dementia associated with amyotrophic lateral sclerosis (als) known as (ftd-als) includes the symptoms of ftd (behavior, language and movement problems) co-occurring with amyotrophic lateral sclerosis (loss of motor neurons). two ftd-related disorders are progressive supranuclear palsy (also classed as a parkinson-plus syndrome), and corticobasal degeneration. these disorders are tau-associated. huntington's disease huntington's disease is a neurodegenerative disease caused by mutations in a single gene htt, that encodes for huntingtin protein. symptoms include cognitive impairment and this usually declines further into dementia. the first main symptoms of huntington's disease often include: difficulty concentrating memory lapses depression - this can include low mood, lack of interest in things, or just abnormal feelings of hopelessness stumbling and clumsiness that is out of the ordinary mood swings, such as irritability or aggressive behavior to insignificant things hiv main article: hiv-associated neurocognitive disorder hiv-associated dementia results as a late stage from hiv infection, and mostly affects younger people. the essential features of hiv-associated dementia are disabling cognitive impairment accompanied by motor dysfunction, speech problems and behavioral change. cognitive impairment is characterised by mental slowness, trouble with memory and poor concentration. motor symptoms include a loss of fine motor control leading to clumsiness, poor balance and tremors. behavioral changes may include apathy, lethargy and diminished emotional responses and spontaneity. histopathologically, it is identified by the infiltration of monocytes and macrophages into the central nervous system (cns), gliosis, pallor of myelin sheaths, abnormalities of dendritic processes and neuronal loss. creutzfeldt–jakob disease creutzfeldt–jakob disease is a rapidly progressive prion disease that typically causes dementia that worsens over weeks to months. prions are disease-causing pathogens created from abnormal proteins. alcoholism main article: alcohol-related dementia alcohol-related dementia, also called alcohol-related brain damage, occurs as a result of excessive use of alcohol particularly as a substance abuse disorder. different factors can be involved in this development including thiamine deficiency and age vulnerability. a degree of brain damage is seen in more than 70% of those with alcohol use disorder. brain regions affected are similar to those that are affected by aging, and also by alzheimer's disease. regions showing loss of volume include the frontal, temporal, and parietal lobes, as well as the cerebellum, thalamus, and hippocampus. this loss can be more notable, with greater cognitive impairments seen in those aged 65 years and older. mixed dementia more than one type of dementia, known as mixed dementia, may exist together in about 10% of dementia cases. the most common type of mixed dementia is alzheimer's disease and vascular dementia. this particular type of mixed dementia's main onsets are a mixture of old age, high blood pressure, and damage to blood vessels in the brain. diagnosis of mixed dementia can be difficult, as often only one type will predominate. this makes the treatment of people with mixed dementia uncommon, with many people missing out on potentially helpful treatments. mixed dementia can mean that symptoms onset earlier, and worsen more quickly since more parts of the brain will be affected. genetics although it is not very common to inherit dementia from a parent or grandparent, there are genetic linked causes of dementia. these are only a small overall portion of the overall cases of dementia, but it is possible. other chronic inflammatory conditions that may affect the brain and cognition include behçet's disease, multiple sclerosis, sarcoidosis, sjögren's syndrome, lupus, celiac disease, and non-celiac gluten sensitivity. these types of dementias can rapidly progress, but usually have a good response to early treatment. this consists of immunomodulators or steroid administration, or in certain cases, the elimination of the causative agent. a 2019 review found no association between celiac disease and dementia overall but a potential association with vascular dementia. a 2018 review found a link between celiac disease or non-celiac gluten sensitivity and cognitive impairment and that celiac disease may be associated with alzheimer's disease, vascular dementia, and frontotemporal dementia. a strict gluten-free diet started early may protect against dementia associated with gluten-related disorders. cases of easily reversible dementia include hypothyroidism, vitamin b12 deficiency, lyme disease, and neurosyphilis. for lyme disease and neurosyphilis, testing should be done if risk factors are present. because risk factors are often difficult to determine, testing for neurosyphilis and lyme disease, as well as other mentioned factors, may be undertaken as a matter of course where dementia is suspected.: 31–32 many other medical and neurological conditions include dementia only late in the illness. for example, a proportion of patients with parkinson's disease develop dementia, though widely varying figures are quoted for this proportion. when dementia occurs in parkinson's disease, the underlying cause may be dementia with lewy bodies or alzheimer's disease, or both. cognitive impairment also occurs in the parkinson-plus syndromes of progressive supranuclear palsy and corticobasal degeneration (and the same underlying pathology may cause the clinical syndromes of frontotemporal lobar degeneration). although the acute porphyrias may cause episodes of confusion and psychiatric disturbance, dementia is a rare feature of these rare diseases. limbic-predominant age-related tdp-43 encephalopathy (late) is a type of dementia that primarily affects people in their 80s or 90s and in which tdp-43 protein deposits in the limbic portion of the brain. hereditary disorders that can also cause dementia include: some metabolic disorders such as lysosomal storage disorders, leukodystrophies, and spinocerebellar ataxias. diagnosis symptoms are similar across dementia types and it is difficult to diagnose by symptoms alone. diagnosis may be aided by brain scanning techniques. in many cases, the diagnosis requires a brain biopsy to become final, but this is rarely recommended (though it can be performed at autopsy). in those who are getting older, general screening for cognitive impairment using cognitive testing or early diagnosis of dementia has not been shown to improve outcomes. however, screening exams are useful in 65+ persons with memory complaints. normally, symptoms must be present for at least six months to support a diagnosis. cognitive dysfunction of shorter duration is called delirium. delirium can be easily confused with dementia due to similar symptoms. delirium is characterized by a sudden onset, fluctuating course, a short duration (often lasting from hours to weeks), and is primarily related to a somatic (or medical) disturbance. in comparison, dementia has typically a long, slow onset (except in the cases of a stroke or trauma), slow decline of mental functioning, as well as a longer trajectory (from months to years). some mental illnesses, including depression and psychosis, may produce symptoms that must be differentiated from both delirium and dementia. these are differently diagnosed as pseudodementias, and any dementia evaluation needs to include a depression screening such as the neuropsychiatric inventory or the geriatric depression scale. physicians used to think that people with memory complaints had depression and not dementia (because they thought that those with dementia are generally unaware of their memory problems). however, researchers have realized that many older people with memory complaints in fact have mild cognitive impairment the earliest stage of dementia. depression should always remain high on the list of possibilities, however, for an elderly person with memory trouble. changes in thinking, hearing and vision are associated with normal ageing and can cause problems when diagnosing dementia due to the similarities. given the challenging nature of predicting the onset of dementia and making a dementia diagnosis clinical decision making aids underpinned by machine learning and artificial intelligence have the potential to enhance clinical practice. cognitive testing