Types of Dementia

The World Health Organization (WHO) defines mental health as a "state of well-being in which the individual realizes his or her own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to his or her community".

Dementia is one of the prevalent mental illnesses, which is more common in the elderly. Characterized by a decline in the functioning of the brain, it is an illness that results in the loss of mental functions like thinking, memory, reasoning, and overall cognitive abilities. Some of the common symptoms include loss of memory, changes in personality, mood, and behavior.

Types of Dementia
Based on the portion of the brain affected, dementia is categorized into two main types: cortical and sub-cortical.

These are a result of a disorder in the cerebral cortex. The Alzheimer's disease is one of the common types. The cerebral cortex is a structure within the brain, which plays an important role in memory, perceptual awareness, language, thought, consciousness, and attention.

It comprises three important parts, which are sensory, motor, and association areas. The sensory areas receive and process information from the senses, while the association areas function to produce a meaningful perceptual experience, process languages and thoughts, and help us to interact effectively.

The motor areas, on the other hand, help to execute and select voluntary movements.

Alzheimer's Disease:  Also known as Senile Dementia of the Alzheimer Type (SDAT), this is an incurable, degenerative disorder. Alois Alzheimer, a German psychiatrist, was the first one to describe it. During Alzheimer's disease, the brain of the affected person shows characteristically abnormal behavior.

The brain cells produce reduced amounts of neurotransmitters, which are chemicals required for communication between nerves. The most common symptom is serious memory problem, which can affect everyday activities. Early diagnosis is crucial for effective treatment.

Dementia with Lewy Bodies (DLB): This is characterized by the presence of Lewy bodies, which are abnormal aggregates of protein, developed inside nerve cells. Although the causes of this type of dementia are not well understood, a locus at a gene called PARK11 is supposed to be associated with the disease. .

Several symptoms and pathology of DLB are similar to Alzheimer's and Parkinson's diseases. The diagnosis often involves detection of Lewy bodies, loss of dopamine-producing neurons, and a loss of acetylcholine-producing neurons.

People suffering from DLB exhibit fluctuating cognition, with variation in attention and alertness, accompanied by hallucinations, syncope, transient loss of consciousness, and hypersensitivity to neuroleptic medication

Vascular Dementia: Also known as multi-infarct dementia, this is a degenerative cerebrovascular disease, marked by a decline in the brain functions. Often, it is caused by a series of small strokes that damage the cerebral cortex, and hamper understanding of language, instructions, and the memory.

Some of the early symptoms also include mild weakness in the limbs, slurred speech, dizziness, and impairment in short-term memory.

More prominent symptoms include prominent loss in memory, loss of control over bladder and bowel movements, difficulty in following instructions, lack of verbal fluency, slowing of the processing ability, and hampered abstract thinking.

Frontotemporal Lobar Degeneration (FTLD): This refers to the group of disorders associated with atrophy in the frontal lobe and the temporal lobe of the brain. It is the fourth most common type of dementia. Clinically, there are three subtypes of FTLD: frontotemporal dementia, semantic dementia, and progressive nonfluent aphasia.

Frontotemporal dementia (FTD) is caused by degeneration of the frontal lobe of the brain, and may extend to the temporal lobe. Semantic dementia (SD) is a progressive neurodegenerative disorder, marked by loss of semantic memory. Progressive nonfluent aphasia is marked by progressive difficulties in speech.

Alcohol Induced Persisting Dementia: Also known as Alcohol Dementia, this disorder is associated with excessive continuous consumption of alcohol. The common types of disorders in this category include the Korsakoff's syndrome, Wernicke's encephalopathy, or the Wernicke-Korsakoff syndrome, which is a combined manifestation of the first two.

Prominent symptoms of the Korsakoff syndrome include anterograde amnesia, retrograde amnesia, confabulation, lack of insight, and apathy, which are caused by thiamine deficiency. The onset of Wernicke's encephalopathy is usually abrupt, and is marked by gait ataxia, confusion, short-term memory loss, confabulation, and several eye movement disorders.

The Wernicke-Karsakoff syndrome exhibits combined symptoms of both the disorders. Some of the common signs include memory loss, difficulty performing familiar tasks, impaired judgment, problems with language, and changes in personality.

Unlike other forms of dementia, which are common only in elderly people, anyone (regardless of age), who is a regular heavy drinker, is at risk for succumbing to alcohol-related dementia.

Creutzfeldt-Jakob Disease: Creutzfeldt-Jakob disease (CJD) is a fatal degenerative neurological disorder. Known to be related to the mad cow disease, the symptoms of CJD are similar to those of Alzheimer's disease, the only difference being that the former progresses much faster.

There are three types or variants: sporadic, hereditary, and acquired. Sporadic form is the most common, in which disease appears without exhibition of any risk factors. The hereditary case is that in which a person has a family history of CJD, and tests positive for the genetic mutation associated with it.

The acquired CJD is transmitted by exposure of brain or nervous system tissue. Initial symptoms include speech impairment, blurred vision, insomnia, personality changes, anxiety, memory loss, impaired thinking, and impaired muscle coordination as well.

The symptoms aggravate as the disease progresses, and in many cases, the patient may lapse into coma. The disease becomes fatal, the most common causes of death being heart failure, respiratory failure, pneumonia, or other infections.

Dementia Pugilistica: Harrison S. Martland was the first to describe dementia pugilistica in the year 1928. Also known as chronic traumatic encephalopathy (STE), Boxer's Dementia, or the Punch-drunk syndrome, this is a neurological disorder, which is common in boxers and wrestlers, owing to the repeated concussions during the matches.

The most common symptoms include declining mental abilities, memory loss, tremors, lack of coordination, speech problems, and pathological paranoia. The patient's brain tends to lose neurons, and the pyramidal tract in the brain becomes dysfunctional.

Common causes that lead to this disorder are loss of neurons, hydrocephalus, collection of proteinacious and senile plaques, diffuse axonal injury, attenuation of corpus callosum, neurofibrillary tangles, and damages to the cerebellum.

Moyamoya Syndrome: The angiographic image for a person suffering from this disease looks like a puff of smoke, which is how Moyamoya loosely translates from Japanese, and hence the name of the disorder.

This syndrome is a progressive neurological disorder, affecting the blood vessels in the brain. It is characterized by the narrowing and/or closing of the carotid artery. Inadequate blood supply leads to decrease in the oxygen supply to the brain, and remains to be the prominent cause.

The disorder can either be congenital or acquired. Patients suffering from Down syndrome, neurofibromatosis, or sickle cell disease, are vulnerable to Moyamoya syndrome. Diagnosis is usually done with the help of computed tomography (CT), magnetic resonance imaging (MRI), or an angiogram.

Benson's Syndrome: Also known as the Posterior Cortical Atrophy, this syndrome is the visual variant of the Alzheimer's disease, and was first described by Franck Benson in 1988. It causes shrinkage of the cortex (the posterior part of the brain).

The early symptoms usually start appearing after the age of fifty. Some of them include blurred vision, problems with depth perception, and difficulty in reading. As it progresses, the condition aggravates, and the person might show mis-recognition of familiar faces and objects, or even suffer from hallucinations.

These are a result of dysfunction in the parts of the brain, beneath the cortex. The symptoms and signs differ largely from the cortical dementia disorders.

Huntington's Disease: This is named after the American Physician George Huntington, who first described this disease in the year 1872. It is a genetic neurological disorder, which affects the nerve cells in the brain, and results in uncontrolled and uncoordinated body movements (called chorea), emotional disturbance, and decline in cognitive abilities.

It is a trinucleotide repeat disorder, which means that it is caused owing to the length of a repeated sequence of a gene, exceeding the normal gene. The normal gene is called the Huntington gene, and is referred to as HTT, while the mutant gene is referred to as mHtt.

The symptoms for this disease include chorea, slurred speech, and other psychological symptoms of dementia.

Dementia Due to Metabolic Abnormalities: In addition to several other reasons, there are a few metabolic abnormalities which can lead to dementia.

• Decreased thyroid function, medically termed as hypothyroidism, results in depression that is similar to dementia.

• Hypoglycemia, a medical condition in which there is a lack of adequate sugar in the bloodstream, can cause confusion or personality changes.
• Pernicious anemia, caused by failure to absorb vitamin B-12, also can cause cognitive changes, and lead to dementia.

• The beriberi disease, marked by deficiency of Vitamin B1 or Thiamine, can also cause dementia.
• Folate deficiency can also be a cause.

Dementia Due to Parkinson's Disease: Also known as Primary Parkinsonism or Idiopathic Parkinson's Disease, this is a chronic and progressive neurodegenerative disorder, affecting the central nervous system (CNS).

It further results in impairment of the patient's motor skills as well as other functions which are controlled by the CNS. It is characterized by muscle rigidity, bradykinesia, tremor, and in some cases, akinesia, which means loss of physical movement.

All the symptoms are a result of the degeneration of brain cells that produce dopamine, particularly those located in the locus coeruleus and the substantia nigra.

Dementia Due to Subdural Hematoma: Subdural Hematoma is a form of brain injury, in which blood gathers between the outer protective covering of the brain (dura) and the middle layer of the meninges (arachnoid).

The bleeding separates the dura and the arachnoid layers, and may cause a rise in the intracranial pressure (ICP), which can cause compression and damage to the delicate brain tissues.

Signs and symptoms include history of recent head injury, loss of consciousness, amnesia, nausea, vomiting, numbness, dizziness, disorientation, blurred vision, ataxia, personality changes, slurred speech, seizures, and constant or fluctuating pain.

AIDS Dementia Complex: This is a neurological disorder that is associated with HIV infection and AIDS. It is a metabolic encephalopathy, induced by HIV infection, and caused by the immune activation of brain macrophages and microglia.

It is characterized by impaired cognitive abilities, motor dysfunction, behavioral changes, and speech problems. The cognitive disabilities usually include mental slowness, poor concentration, and mild loss of memory.

The motor symptoms include clumsiness, poor balance, and tremors. The behavioral changes include lethargy, diminished emotional response, and apathy. Dementia is diagnosed in the AIDS Dementia complex usually when the cognitive impairment in the patient is severe enough to hamper the routine day-to-day functions.

The severity of the symptoms increases as the disease progresses. The normal, sub clinical, and mild stages lead to moderate and severe cases, and reach the severe stage in which the intellectual and social comprehension and responses are at a rudimentary level. The person becomes paraparetic or paraplegic with urinary and/or fecal incontinence.

PseudoDementia: It is a severe form of depression, resulting from a progressive brain disorder, in which cognitive symptoms mimic those of dementia. It is usually seen in older people, and the symptoms are similar to dementia, but the cause is a pre-existing psychiatric illness, and not a degenerative one.

The history of disturbance in this disorder is a short and abrupt onset unlike in dementia, where it is more dangerous. Clinically, people with pseudodementia can be differentiated from those with dementia when their memory is tested.

People with pseudodementia will often answer that they don't know the answer to a question, but their attention and concentration are intact, and they appear upset or distressed. On the other hand, people suffering from Dementia will often give wrong answers, have poor concentration, and will appear indifferent.

Hence, this classification shall help your understanding of this complex, neurological condition. You should now be able to better understand the behavior of patients as well.