Sietske N. Heyn is a medical writer with a PhD in neuroscience. Dr. Heyn's education includes a BS with honors from the University of Oregon, and a doctoral degree in neuroscience from the University of California at Davis. After completing postdoctoral training at the University of California, San Francisco, and many years of working as a medical writer at the Stanford University Center for Down Syndrome Research, Dr. Heyn now runs her own medical writing business.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Parkinson's disease is the second most common neurodegenerative disorder and
the most common movement disorder. It is characterized by progressive loss of
muscle control, which leads to trembling of the limbs and head while at rest,
stiffness, slowness, and impaired balance. As symptoms worsen, it may become
difficult to walk, talk, and complete simple tasks.
The progression of Parkinson's disease and the degree of impairment vary from
individual to individual. Many people with Parkinson's disease live long
productive lives, whereas others become disabled much more quickly. Premature
death is usually due to complications such as falling-related injuries or
pneumonia.
In the United States, about 1 million people are affected by Parkinson's
disease and worldwide about 5 million. Most individuals who develop Parkinson's
disease are 60 years of age or older. Parkinson's disease occurs in
approximately 1% of individuals aged 60 years and in about 4% of those aged 80
years. Since overall life expectancy is rising, the number of individuals with
Parkinson's disease will increase in the future. Adult-onset Parkinson's disease
is most common, but early-onset Parkinson's disease (onset between 21-40 years),
and juvenile-onset Parkinson's disease (onset before age 21) also exist.
Descriptions of Parkinson's disease date back as far as 5000 BC. Around that
time, an ancient Indian civilization called the disorder Kampavata and treated
it with the seeds of a plant containing therapeutic levels of what is today
known as levodopa. Parkinson's disease was named after the British doctor James
Parkinson, who in 1817 first described the disorder in great detail as "shaking
palsy."
What causes Parkinson's disease?
A substance called dopamine acts as a messenger between two brain areas - the
substantia nigra and the corpus striatum - to produce smooth, controlled
movements. Most of the movement-related symptoms of Parkinson's disease are
caused by a lack of dopamine due to the loss of dopamine-producing cells in the
substantia nigra. When the amount of dopamine is too low, communication between
the substantia nigra and corpus striatum becomes ineffective, and movement
becomes impaired; the greater the loss of dopamine, the worse the
movement-related symptoms. Other cells in the brain also degenerate to some
degree and may contribute to non-movement related symptoms of Parkinson's
disease.
Although it is well known that lack of dopamine causes the motor symptoms of
Parkinson's disease, it is not clear why the dopamine-producing brain cells
deteriorate. Genetic and pathological studies have revealed that various
dysfunctional cellular processes, inflammation, and stress can all contribute to
cell damage. In addition, abnormal clumps called Lewy bodies, which contain the
protein alpha-synuclein, are found in many brain cells of individuals with
Parkinson's disease. The function of these clumps in regards to Parkinson's
disease is not understood. In general, scientists suspect that dopamine loss is
due to a combination of genetic and environmental factors.
The primary symptoms of Parkinson's disease are all related to voluntary and
involuntary motor function and usually start on one side of the body. Symptoms
are mild at first and will progress over time. Some individuals are more
affected than others. Characteristic motor symptoms include
the following:
Tremors: Trembling in fingers, hands, arms, feet, legs, jaw, or head.
Rigidity: Stiffness of the limbs and trunk, which may increase
during movement. Rigidity may produce muscle aches and pain.
Bradykinesia: Slowness of voluntary movement.
Postural instability: Impaired or lost reflexes can make it
difficult to adjust posture to maintain balance.
Parkinsonian gait: Individuals with more progressive Parkinson's
disease develop a distinctive shuffling walk with a stooped position and a
diminished or absent arm swing.
Secondary symptoms of Parkinson's disease
Some of the secondary symptoms include:
anxiety, insecurity, and stress,
confusion,
memory loss, and
dementia (more common in elderly individuals),
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