Last week’s blog discussed how Parkinson’s disease and two types of dementia are all members of the Lewy body family. This week expands on that with a more scientific view. Also, new research has suggested another member of the family, REM Sleep Behavior Disorder.
Damaged alpha-synuclein proteins clump together to form the microscopic round deposits called Lewy bodies. Unlike Alzheimer’s damaged proteins, found only in the cerebral cortex, Lewy bodies can be found in many areas of the brain. Besides dementia, these damaged proteins can cause motor problems, autonomic nervous system (ANS) dysfunctions, perceptual problems, mood disturbances and more, depending on where they are in the body.
At present, identifying the presence of Lewy bodies other than by their symptoms is difficult but that is changing. Brain scans are getting more accurate and researchers are actually finding Lewy bodies in other, more easily accessed areas of the body, like the gastro-intestinal (GI) tract.
Alzheimer’s damaged proteins are thug-like, attacking and killing whatever neurons (brain cells) they touch. Lewy bodies are more selective, choosing only those neurons that contain certain neurotransmitters—chemicals that the cells need to function properly. They extract the chemicals, leaving the cells weakened and eventually dead. The targeted neurotransmitters vary, depending on the area of the brain.
Parkinson’s Disease. In the mid-brain, Lewy bodies extract the chemical dopamine, instrumental in fine motor control. This results in the motor symptoms of Parkinson’s disease. Although PD starts out as a movement disorder, other symptoms appear the disease progresses. One of the most distressing is dementia. (See our 6/15/12 and 10/12/12 blogs.)
Lewy Body Dementia. While this term was once synonymous with Dementia with Lewy Bodies, it is now an umbrella term that defines both types of dementia caused by Lewy bodies: dementia with Lewy bodies (DLB) and Parkinson’s disease with dementia (PDD).
Dementia with Lewy Bodies (DLB). Dementia is defined as a loss of cognitive skills such as memory, thinking, or impulse control, severe enough to interfere with functional ability or activities of daily living. Such losses occur when Lewy bodies in the cerebral cortex target the chemical, acetylcholine. When no PD is involved, the resulting disorder is called Dementia with Lewy Bodies.
Parkinson’s Disease with Lewy Bodies (PDD). When someone with PD develops dementia, it means that the Lewy bodies have traveled from the midbrain to the cortex. Both dopamine and acetylcholine are targeted, which causes both motor and dementia symptoms.
People with PD (PwPD) are a ready-made group of people at risk for dementia. Therefore most of the subjects in the growing pool of research about early- and pre-Lewy body dementia are PwPD. However, it is important to remember that LBD doesn’t have to start with Parkinson’s. It can skip the PD and go right to dementia—and then of course, it’s called Dementia with Lewy bodies. Even so, since two types are so similar, almost everything researchers learn about PDD and its precursors, we can also apply to DLB, that is, to LBD in general.
REM Sleep Behavior Disorder (RBD). Caregivers sometimes call RBD “Active Dreams” because the chemical switch that prevents movement during normal dreams is damaged. While RBD has been known to appear in childhood, it is more common after 50. A PwRBD can be very active, thrashing their limbs around, talking and even walking in their sleep. (See our 11/2/12 blog.)
Although RBD can occur alone, it is very common with PD and both types of Lewy body dementia. When researchers autopsied brains from people who died with RBD, they found Lewy bodies even when no other LB disorder was present. Thus we include it here as a Lewy body disorder, usually the first one to appear.
Next week’s blog will be about disorders related to LBD and some lookalikes.