Dementia with Lewy bodies is the second most frequent cause of hospitalization for dementia, after Alzheimer's disease.
Current estimates are that about 60-to-75% of diagnosed dementias are
of the Alzheimer's and mixed (Alzheimer's and vascular dementia) type,
10-to-15% are Lewy Bodies type, with the remaining types being of an
entire spectrum of dementias including frontotemporal lobar degeneration, alcoholic dementia, pure vascular dementia, etc.
Dementia with Lewy Bodies (DLB) exhibits clinical overlap between Alzheimer's disease and Parkinson's disease. Pathologically, it is characterized by development of abnormal proteinaceous (alpha-synuclein) cytoplasmic inclusions, called Lewy bodies,
throughout the brain. These inclusions have similar structural features
to "classical" Lewy Bodies seen subcortically in Parkinson's disease.
Additionally, there is a loss of dopamine-producing neurons (in the substantia nigra) similar to that seen in Parkinson's disease, and a loss of acetylcholine-producing neurons (in the basal nucleus of Meynert and elsewhere) similar to that seen in Alzheimer's disease. Cerebral atrophy (or shrinkage) also occurs as the cerebral cortex
degenerates. Autopsy series have revealed that the pathology of DLB is
often concomitant with the pathology of Alzheimer's disease. That is,
when Lewy Body inclusions are found in the cortex, they often co-occur
with Alzheimer's disease pathology found primarily in the hippocampus, including: neurofibrillary tangles (abnormally phosphorylated tau protein), senile plaques (deposited beta-amyloid protein), and granulovacuolar degeneration.
Within DLB, the loss of cholinergic (acetylcholine-producing)
neurons is thought to account for the degradation of cognitive and
emotional functioning as in Alzheimer's disease, while the loss of
dopaminergic (dopamine-producing) neurons is thought to account for the
degradation of motor control as in Parkinson's disease. Thus, DLB is
similar in some ways to both the dementia resulting from Alzheimer's
disease and Parkinson's disease. In fact, it is often confused in its
early stages with Alzheimer's disease and/or vascular dementia (multi-infarct dementia).
The overlap of neuropathologies and presenting symptoms (cognitive,
emotional, and motor) may make an accurate differential diagnosis
difficult to reach.
Dementia with Lewy Bodies is not a DSM-IV
recognized diagnosis. (Note: DSM-IV was published in 1994.) In 1996, a
consortium of scientists initially proposed and later revised
diagnostic guidelines. Central features of DLB include progressive
cognitive decline, typically with impairments in memory, visual-spatial
abilities, and/or attention. Core features include fluctuating
cognition with variations in attention and alertness, recurrent visual hallucinations
(typically early in the disease), and motor features of parkinsonism.
DLB patients also often experience repeated falls, syncope (fainting),
transient loss of consciousness, and hypersentivity to neuroleptic
medications. Generally, DLB is diagnosed when cognitive symptoms
develop within a year or two of movement disorder/Parkinsonian
symptoms. Recent research suggests that presence of sleep disturbance
may also be useful in differentiating DLB from other forms of dementia.
[edit] Treatment
The treatment of DLB, as with Parkinson's disease, involves striking
a balance between treating the motor and emotive/cognitive symptoms.
Treatment of the movement portion of the disease can typically result
in worsening hallucinations and psychosis, while treatment of the
hallucinations and psychosis can result in worsening movement symptoms.
The use of atypical antipsychotics (especially quetiapine) and cholinesterase inhibitors
(especially rivastagmine) represent the treatments of choice, but these
are all aimed at palliation as there is no cure. The use of memantine
may be recommended, and may represent a means to slow or prevent the
decline of cognitive function, although strong evidence to support or
disprove this is lacking.
Dementia with Lewy bodies (DLB) is also known under a variety of
other names including, Lewy Body dementia (LBD), Diffuse Lewy Body
disease (DLBD), Cortical Lewy Body disease (CLBD), and Senile dementia
of Lewy type. All incorporate the name Lewy, as Dr. Frederick Lewy
(1885-1950) was first to discover the abnormal protein deposits ("Lewy
Body inclusions") in the early 1900s.
Multi-infarct dementia, also known as vascular dementia (VD), is the second most common form of dementia after Alzheimer disease
(AD) in the elderly (persons over 65 years of age). The term refers to
a group of syndromes caused by different mechanisms all resulting in
vascular lesions in the brain. Early detection and accurate diagnosis
are important, as VD is at least partially preventable.
The main subtypes of VD described at the moment are: vascular mild cognitive impairment, multi-infarct dementia, vascular dementia due to a strategic single infarct (affecting the thalamus, the anterior cerebral artery, the parietal lobes or the cingulate gyrus),
vascular dementia due to hemorrhagic lesions, small vessel disease
(which includes vascular dementia due to lacunar lesions and Binswanger
disease), and mixed AD and VD.
Vascular lesions can be the result of diffuse cerebrovascular
disease or focal lesions (or a combination of both, which is what is
observed in the majority of cases). Mixed dementia is diagnosed when
patients have evidence of AD and cerebrovascular disease, either
clinically or based on neuroimaging evidence of ischemic lesions. In
fact VD and AD often coexist, especially in older patients with
dementia.
Frontotemporal dementia (FTD) is one of three clinical syndromes associated with frontotemporal lobar degeneration. FTD selectively affects the frontal lobe of the brain and may extend backward to the temporal lobe.
Symptoms can be classified (roughly) into two groups which underlie
the functions of the frontal lobe: behavioural symptoms (and/or
personality change) and symptoms related to problems with executive
function.
Behavioural symptoms include apathy and aspontaneity or oppositely disinhibition.
Apathetic patients may become socially withdrawn and stay in bed all
day or no longer take care of themselves. Disinhibited patients can
make inappropriate (sometimes sexual) comments or perform inappropriate
acts. Patients with FTD can sometimes get into trouble with the police
because of inappropriate behaviour such as stealing.
Executive function is the cognitive skill of planning and organizing
- patients become unable to perform skills that require complex
planning or sequencing.
Frontotemporal dementia occurs in patients with motor neurone disease (also known in the US as Lou Gehrig's disease or amyotrophic lateral sclerosis)
in a small number of cases. The prognosis for people with MND is worse
when combined with FTD, shortening survival by about a year.[1]
Because FTD often occurs in people who are young (i.e. in their 40's
or 50's) the effects on families can be severe. Patients often still
have children living in the home. Financially, it can be devastating as
the disease strikes at the time of life that are often the top wage
earning years.
Semantic dementia (SD) is a progressive neurodegenerative
disorder characterized by loss of semantic memory in both the verbal
and non-verbal domains. The most common presenting symptoms are in the
verbal domain however (with loss of word meaning) and it is therefore
often characterized (incorrectly) as a primary language disorder (a
so-called progressive fluent aphasia). When the word comprehension
deficits predominate, the patient also fits the criteria for primary progressive aphasia (PPA).
SD is one of the three canonical clinical syndromes associated with frontotemporal lobar degeneration.
SD is a clinically-defined syndrome, but is associated with
predominantly temporal lobe atrophy (left greater than right) and hence
is sometimes called temporal variant FTLD (tvFTLD).
It was first described by Professor Elizabeth Warrington in 1975
(Warrington EK. The selective impairment of semantic memory. Q J Exp
Psychol. 1975 Nov;27(4):635-57) but was not given the name semantic
dementia until 1989 (Snowden JS, Goulding PJ, Neary D. Semantic
dementia: a form of circumscribed cerebral atrophy. Behav Neurol
1989;2:167-182.).
//
[edit] Signs and Symptoms
SD patients often present with the complaint of word-finding
difficulties. On further questioning, patients often appear to have
lost the meaning of certain words (e.g. asking "What is a fish?"). As
the disease progresses, behavioural and personality changes are often
seen similar to those seen in frontotemporal dementia although cases have been described of 'pure' semantic dementia with few late behavioural symptoms.
| 
