Comparisons
Part 4

A comparison of HD to Alzheimer's and Parkinson's diseases

Treatments

Currently there exists no cure for any three of the neurological diseases. As with Huntington’s Disease, treatments for Alzheimer and Parkinson’s can be split into two distinct categories: treatments that target the specific mechanism of the disease, and palliative treatments (eg those that lessen symptoms but do not cure). For HD, mechanisms which are targeted include protein aggregation, inflammation, and free radical damage (See treatments section).

As of this writing (Jan 04), there are five FDA (Federal Drug Administration)-approved drugs that can control symptoms and slow the progression of Alzheimer’s disease. Four of these drugs, Cognex, Aricept, Exelon, and Reminyl belong to a class of drugs known as cholinesterase inhibitors. Each drug acts in a different way to slow the metabolic breakdown of acetylcholine, an important brain chemical involved in nerve cell communication, and to make more available for communication between cells. Those suffering from AD have low levels of acetylcholine, and the medication helps to slow the progression of cognitive impairment and is most effective for patients in the early to middle stages of AD. The fifth drug, Namenda (memantine), is the first drug approved for the treatment of moderate to severe AD. Namenda shields brain cells from overexposure to another brain chemical called glutamate, excess levels of which contribute to the death of brain cells in people with Alzheimer’s. Although all five drugs have all been shown to modestly slow the progression of cognitive symptoms and reduce problematic behaviors in some people, at least half of the people who take these drugs do not respond to them. While the overall treatment effect of these medications is modest, studies show that, when they do work, they can make a significant difference in a person’s quality in life and day-to-day functioning.

Research is now focused upon prevention trials which try to stop the disease process from happening in the first place, and a number of studies are underway to test the effectiveness of various therapies in people without symptoms or who have only slight memory problems. Some of these studies are examining estrogen and various classes of anti-inflammatory and antioxidant chemicals. Research has shown that vitamin E and other antioxidants may slow the progression of AD in some people, although the overall impact is minimal. Research also suggests that ginkgo biloba, an extract made from the leaves of the ginkgo tree, may be of some help in treating AD symptoms. However, here is no evidence that ginkgo will cure or prevent AD. (For more on ginkgo biloba, click here.)

Palliative medications that can control depression, anxiety, agitated behavior (including aggression, hyperactivity and combativeness) and psychotic symptoms can help patients in the middle stages of AD. The medications prescribed for these symptoms are not specifically designated for AD, but they may be considered as part of the treatment plan by the supervising physician. Generally, medications for these symptoms are considered when non-medicated alternatives have failed and/or these symptoms put the AD patients, or others, in danger.

The purpose of all medicines for Parkinson’s disease is to help control tremor, movement, and balance to maintain daily activities. One of the mechanisms targeted by Parkinson’s medications includes the interactions of dopamine, a neurotransmitter (chemical messenger) that affects brain processes by allowing nerve cells to communicate with one another in the brain. Scientists have determined that people with late PD have lost more than 80 percent of dopamine-producing cells in the substantia nigra, an area deep within the brain. Normally, these cells communicate with other brain cells in the nearby striatum via dopamine. Thus, without dopamine, the striatum can’t send out certain messages and the symptoms of Parkinson’s ensue. Levodopa, also called L-dopa, was the earliest treatment discovered for Parkinson’s disease. L-dopa is a method of dopamine replacement therapy; it is turned into dopamine in the brain to supplement the cells that are producing less.

Another group of medications fit into the category of dopamine antagonists, drugs that bind but don’t stimulate dopamine receptors. Antagonists can prevent or reverse the actions of dopamine by keeping dopamine from attaching to receptors; they help improve control of various body movements, which begin to slow or become irregular in early Parkinson’s disease. Dopamine antagonists work by copying the effect of the neurotransmitter dopamine, proving effective in people with Parkinson’s disease who are losing their dopamine-producing cells. By doing this, dopamine antagonists can help people maintain their daily activities. Furthermore, anticholinergic drugs can be used to treat mild symptoms of Parkinson’s disease. Anticholinergic drugs block a neurotransmitter that affects dopamine so that more dopamine is available in the brain. Other pharmacological medications exist to treat Parkinson’s, and they too usually involve the mimicking or replacement of dopamine.

Last Modified: 5-20-04

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