Epidemiology
Roughly 4 million Americans currently have Alzheimer’s disease, and this number is projected to increase to 16-19 million by 2050 (National Institute on Aging and U.S. Census Bureau).
In a large-scale, prospective cohort study by Laurin et al, high levels of physical activity in > 65-year-old women were associated with reduced risks of 42%, 50%, and 37% for cognitive impairment, Alzheimer’s disease, and dementia of any type, respectively. A significant dose-response relationship showed decreasing risk with increasing levels of physical activity. Men did not show this effect in the same study, and the investigators speculated that the number of male subjects could have been too small. Laurin et al hypothesized that the neuroprotection might have been attained by sustaining cerebral blood flow; by limiting increases in resting blood pressures, lowering lipid levels, inhibiting platelet agreeability, and enhancing cerebral metabolic demands; by improving cerebral nutrient supply and angiogenesis; or by a combination of the above. These hypotheses have yet to be proven.
Sedentary lifestyle may be a risk factor in neurodegenerative diseases because it is associated with higher risk of stroke and is more pronounced in the elderly. Studies have found that physical activity either delays loss of, or has no effect on, cognitive function in elderly subjects. However, no studies have reported an accelerated loss of cognitive function with physical activity.
Lindsay et al2 have suggested that regular physical activity could represent a novel and safe preventive strategy against Alzheimer’s disease and many other conditions, and it should be examined further. Interestingly, among patients with COPD, acute exercise was associated with improved performance on the verbal fluency test, a measure of verbal processing.
Intermediate Mechanisms
Several animal studies indicate a beneficial effect of exercise on the central nervous system (CNS), and are described briefly here.
- Aged sedentary rats had 11% fewer Purkinje cells and 9% smaller Purkinje cell soma volumes than aged rats who exercised. Indeed, aged rats that exercised had the same number of Purkinje cells as young rats, thereby suggesting that the degree of age-associated degenerative changes in parts of the CNS are dependent on earlier lifestyle and health habits, and may be prevented or delayed by physical exercise.
- Physical activity in rats produced 2- to 12-fold enhancements in spatial learning performance on both the Morris and place learning-set probe trials, respectively.
- Physical activity also attenuated motor deficits and impeded age-related neuronal loss.
- Physical activity increased the discharge frequency of pyramidal cells and interneurons as long as the animal ran continuously on the wheel. Furthermore, the discharge frequency of pyramidal cells and interneurons increased with increasing running velocity, even though the frequency of hippocampal theta waves remained constant.
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January 25th, 2011 :: Filed under
Parkinson's
Until recently, most people thought of Parkinson’s disease as something that afflicted only older people. Many were surprised when one of the younger generation, Michael J. Fox, announced that he had to drop out of the popular television series Spin City due to persistent Parkinson’s symptoms. Former U.S. attorney general Janet Reno further alerted the U.S. populace that Parkinson’s could no longer be ignored when her tremors became so persistent that she could no longer keep them a secret. Although these two examples have high visibility, these individuals are not alone. Last year, over 1.5 million Americans were believed to have Parkinson’s disease, a chronic, slowly progressive neurological condition that typically affects those over the age of 50. Rates of Parkinson’s have quadrupled in the past 30 years and may increase even more dramatically as growing numbers of baby boomers reach and pass age 60. The hallmark of Parkinson’s disease, and the symptom most commonly associated with it, is a tremor, or form of “shaking palsy.” These tremors can become so severe that the simplest task, such as eating with a fork or brushing one’s teeth, can become difficult. These additional symptoms may also occur:
• Tremor of the hand when in a relaxed position or when under stress
• Rigidity or stiffness in the muscles
• Slowness in movement and a delay in initiating movements
• Poor balance
• Difficulty in walking, shuffling steps, and inability to take next steps
• Slurred speech, slowness in thought, and small, cramped handwriting
Although there are many theories that exist concerning the causes of this disease, the most common appear to be these:
• Familial predisposition (about 15-20 percent of those who have Parkinson’s have a close relative with it)
• Accelerated aging
• Exposure to environmental toxins such as pesticides
Parkinson’s is progressive and incurable; however, new drug therapies, including levodopa, dopamine antagonists, and MAO inhibitors, work to keep the symptoms under control, in most cases for months and years. Surgical options have also provided promising results, such as brain tissue transplants and the use of fetal tissue or genetically engineered cell transplant. Both of these alternatives offer hope for the future.
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January 18th, 2011 :: Filed under
Parkinson's
Confirmatory Testing
Confirmatory testing is usually done through Western blot testing. These tests are very specific, making false- positive results extremely unlikely.
A positive ELISA followed by a positive Western blot confirms the diagnosis of chronic HIV infection. Upon reporting these results to patients, physicians commonly encounter denial. It may be reasonable in limited circumstances to offer repeat testing to a patient who believes his or her test to be falsely positive, but the provider should pursue other testing (e.g., CD4 count, hepatitis testing, complete blood cell count) assuming that the repeat test finding will also be positive.
Western blot tests should not be used for screening, as their sensitivity is unacceptably low. Circumstances in which an ELISA may not be optimal for screening should prompt consultation with a specialist, not the use of Western blot testing as an alternative.
Cell Subset Analysis
T cell subset analysis should never be used to diagnose HIV infection.
Most providers are familiar with the decline in CD4 cells that is the hallmark of chronic HIV infection. However, the CD4 cell count can fluctuate in normal populations and can be very low in HIV-negative patients who are acutely ill or treated with corticosteroids. Therefore, although leucopenia and lowCD4 cell count are common in patients with chronic HIV infection and may prompt consideration for HIV testing, these measures should never be used as adjunctive HIV tests.
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January 11th, 2011 :: Filed under
HIV