Dementia With Lewy Bodies – An Underrated Diseaseby Sara Adaes, PhD | January 18, 2016
Friedrich Heinrich Lewy was a German neurologist born in 1885 who moved to the United States in 1934 to escape from Nazi Germany. He lived and worked in the US until his death in 1950. In 1912, while studying Parkinson’s disease (at the time known as Paralysis agitans), Lewy discovered abnormal protein deposits in the brain of Parkinson’s patients that somehow disrupted the normal functioning of the brain. These deposits later became known as “Lewy bodies”.
We now know that Lewy bodies are neuronal deposits made up of alpha-synuclein protein aggregates and that they are associated with a number of neurological conditions, collectively called “Lewy body disease”. Parkinson’s disease is one of the conditions characterized by the accumulation of Lewy bodies in neurons.
The motor symptoms of Parkinson’s disease result from the accumulation of Lewy bodies in dopamine-producing neurons in the substantia nigra, a region of the midbrain, causing the depletion of this neurotransmitter. These motor symptoms are collectively known as Parkinsonism.
Parkinsonism is not the same thing as Parkinson’s disease: Parkinsonism refers to a set of clinical symptoms that include tremor, slowness of movement, rigidity, and postural instability; Parkinson’s disease is a neurodegenerative illness that includes these symptoms.
But the deposition of Lewy bodies in the brain can also lead to the onset of dementia. Lewy Body Dementia is an umbrella term that includes clinically diagnosed dementias in which Lewy bodies are found, including Parkinson’s disease dementia.
Indeed, although Parkinson’s disease has been classically regarded as a motor disorder, the cognitive deficits associated with the disease are now being increasingly acknowledged. Dementia usually develops in around 25% of Parkinson’s patients, but the risk increases with duration of disease, reaching 50% after 10 years and up to 80% for patients who survive for more than 10 years.
This “Parkinson’s disease dementia” is defined as dementia starting one year or more after Parkinson’s disease is well-established; it is a consequence of the progression of the disease. But there’s another type of Lewy body dementia called “dementia with Lewy bodies” (notice the subtle difference in terminology). This is a type of dementia that occurs before or alongside Parkinsonism, or within one year of onset of motor symptoms.
So, Parkinson’s disease dementia is a type of Lewy body dementia, but it is not dementia with Lewy bodies – this is a different clinical entity. Basically, they differ in the sequence of onset of dementia vs Parkinsonism.
It’s a bit confusing, I reckon.
Dementia with Lewy bodies and Parkinson’s disease dementia share many features, becoming increasingly similar with disease progression. They can be viewed as a continuum and are most likely two clinical representations of a spectrum of Lewy body disease. These disorders are primarily differentiated based on the time-course of the symptoms and some clinical features, but the main pathological difference lays on the patterns of Lewy body distribution.
In Parkinson’s disease, Lewy bodies interfere mainly with the production of dopamine in the midbrain. In dementia with Lewy bodies, on the other hand, these protein aggregates are found diffusely distributed throughout other areas of the brain, including the cerebral cortex. The neurotransmitter acetylcholine is depleted, affecting perception, thinking and behavior. Its symptoms can include visual hallucinations, movement disorders, dizziness, falls, confusion, reduced attention span, memory loss, sleep difficulties, drowsiness, staring into space, daytime naps, disorganized speech, and depression.
Dementia with Lewy bodies is a hugely underrated neurodegenerative disease. It is actually fairly common, although epidemiological data is highly discordant. But studies that aimed at identifying dementia with Lewy bodies that included a neurological examination showed that 16–24% of dementia patients have dementia with Lewy bodies.
In the clinical practice, dementia with Lewy bodies is highly underdiagnosed mostly because, given its symptoms, it is often misdiagnosed as Alzheimer’s disease, in early stages, and with Parkinson’s disease dementia, when patients develop Parkinsonism.
The treatment of dementia with Lewy bodies is complex. Due to the lack of disease-modifying drugs, treatment is directed towards symptoms. And the fact that it is often misdiagnosed is also an obvious problem. Hopefully, an increased knowledge of this disease will lead to better diagnostic criteria and better healthcare.
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