Parkinson's disease (PD) is a disorder of the central nervous system, involving
primarily a degeneration of certain nerve cells in deep parts of the brain called
the basal ganglia, and in particular a loss of nerve cells (or neurons) in a part
of the brainstem called the substania nigra. These cells make the neurochemical messenger dopamine, which is partly responsible for starting a
circuit of messages that coordinate normal movement. In the absence (or with substantial reduction, more than 80% of the normal level) of dopamine, the
neurons in the receiving area (called dopamine receptors) in the next part of the basal ganglia circuit called the Striatum are not adequately stimulated, and
the result is impairment of movement with tremor, stiffness, or balance problems, among other symptoms, which will be discussed in the next section.
Under the microscope, the damaged and dying neurons in the substantia nigra show a round, cellular marker called a Lewy body, which is considered the
specific pathologic hallmark of PD. Because of this, the disorder is sometimes called Lewy body PD, Lewy body parkinsonism, or simply Lewy body disease.
PD occurs in roughly the same proportions in men and women (although there may be a slight preponderance of affected men) throughout the world.
Initial symptoms may appear at any age, although under 40 is uncommon and under 20 is very rare (but it happens). Most commonly, the first symptoms are
noted in the 60’s or 70’s.
Why do these neurons degenerate? The exact reason is not yet known; this topic is a target of significant research, and is discussed further in the
section on the cause of PD.
PD is just one type of parkinsonian syndrome, or parkinsonism. Parkinsonism can be thought of as an umbrella term, encompassing PD and
related syndromes. We will discuss these other conditions in the section on the other syndromes related to PD.
PD is a chronic, usually slowly progressive illness, but the rate of progression will vary from person to person. Although there are many features
of PD that most patients will share, exactly how it affects any given patient is
very individual, and precisely what happens to one patient in the course of the illness may not necessarily follow suit in another. Symptoms in some people
will remain very mild and will not restrict the day-to-day activities for many years, whereas in others will progress to disability much faster.
Diagnosis is based almost exclusively on the history of the person’s illness and the physician’s clinical examination. There are no really adequate
nor specific blood or radiologic tests in common usage to make an absolute diagnosis of PD. Although there is at present nor cure for PD (one can only
cure a disease when one knows the cause), there is a large and growing number of treatments
for the disorder that can improve or even
normalize the quality of life for a very long time.