senile dementia

Dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is a type of dementia characterized by abnormal levels of Lewy bodies, a nervous system protein.

DLB is sometimes described as second only to Alzheimer's disease as a cause of dementia. 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.

Causes

The causes are not yet well understood, but a locus at PARK11 has been described.

Presentation

Dementia with Lewy bodies 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.

History

Dementia with Lewy bodies is not a DSM-IV recognized diagnosis. (Note: DSM-IV was published in 1994.) It is, however, briefly mentioned in the DSM-IV-TR (published in 2000) under Dementia Due to Other General Medical Conditions. 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.

Clinical features

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 hypersensitivity 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.

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 cholinesterase inhibitors represents the treatment of choice. This improves symptoms, but does not cure the disease. 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.

Nomenclature

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. Frederic Lewy (1885-1950) was first to discover the abnormal protein deposits ("Lewy body inclusions") in the early 1900s.

References

External links

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