Fluctuating Cognition and Extra-Pyramidal Signs
Posing questions to an AD and LBD Researcher
Response to Question #1: It's a good question, and one to which I admittedly don't know the whole answer. But, it's kind of like asking why a schizophrenic is not psychotic ALL the time. Or, why an ADHD child is sometime able to control his behavior and at other times is not? Or, why headaches come and then go? These conditions (and LBD), represent disease where the brain episodically does not function normally. I believe that the pathology (damage that is permanent, in our case lewy body inclusions) makes the brain more VULNERABLE to periods of dysfunction. It's similar to how chronic high blood pressure makes one more vulnerable to episodic heart dysfunction (i.e., heart attacks). I believe the pathology (that's always there) makes one vulnerable to episodic failures (waxing and waning of symptoms).
It could very well be some of the things you mentioned. The pathogenesis of the LBD is still not well understood. For that matter, the pathogenesis of AD is also now well understood. We know that certain neuropathologies (lewy bodies, plaques, tangles) located in certain regions of the brain are correlated with certain clinical disease (AD, LBD, PD) that the person showed signs of while living. The mechanism for how the pathology brings about the illness (or perhaps, how the illness brings about the pathology) is not known. For example, in the earliest strains of transgenetic mice (mice genetically manipulated to have AD), it was "easy" to produce a mouse that would go on to develop plaques throughout the brain. The problem was, that the memory impairment (highly correlated with plaques in humans), did not surface in these mice. However, both the pathology and the memory impairment can now be created in recent strains of mice (those mouse guys are getting better at it!). The point is that there is JUST THIS HIGH CORRELATION between neuropathology and disease in humans, but the direction of causality is not known (because we DON'T know the mechanism). Does the disease cause the plaques, or do the plaques cause the disease?
Response to Question #2: The myelin sheath is definitely "hardened" in long-time cigarette smokers, and they are at higher risk for developing dementia... However, I believe that smokers' higher risk comes about due to the damage done to their cardiovascular systems in general... not specifically related to the condition of the sheath. I could, of course, be wrong.
Response to Question #3: LBD involves a lot more than attentional problems. Supplement and special foods have not been proven to help LBD through double-blind placebo controlled trials (as far as I know), with the exception of Vitamin E and some fish oils. 800 IU daily is the right dose of Vitamin E. Levels higher than that have found no dose-related effect (greater benefit).
I jumped the gun a little bit on fish oils. I work closely with a Harvard-trained neurologist, who is of the opinion that one way to reduce the risk for developing dementia is by eating the right foods (i.e., leafy green vegetables). He recommends at least two portions of fish a week, as part of one's diet. There is an ongoing study involving a fish oil pill (The Laxdale Drug Study) in treating the dementia associated with Huntington's disease. We're hopeful that positive findings in that study will also generalize to other dementias such as LBD. So, it may be some time yet before we figure out what fish and fish-oils contribute to helping dementia.
Response to Question #4: It is a problem with the neuronal fibers of the extra-pyramidal system. It is not necessarily problems with the muscle fibers them-selves. Although, over time, muscle fibers will atrophy (waste away) with non-use. I'm not aware of any conclusive research that states that neck rigidity occurs before limb rigidity. However, in my experience, limb rigidity usually occurs first or simultaneously with neck rigidity. Then again, limb rigidity is easier to detect than neck rigidity. In any event, these rigidity problems are associated with dysfunction of the extra-pyramidal system. Two groups of symptoms have been identified: hyperkinetic-dystonic and hypokinetic-rigidity. Both Parkinson's Disease and LBD are classified as hypokinetic-rigidity. Hence, limb and neck rigidity along with tremor, gait disturbances, and other movement or posture problems are classified under the broad term of extra-pyramidal signs (EPS).
Your comments or additional questions are welcome.
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