What is Parkinson’s Disease?
Parkinson’s disease (PD) was first described by Dr. James Parkinson in a little book entitled An Essay on the Shaking Palsy, published in 1817. For the next century, the condition was known popularly as the shaking palsy and in the medical community by its Latin equivalent, paralysis agitans. These terms are misleading, however, implying that people are paralyzed with this disorder, which is not the case. It is sometimes called idiopathic parkinsonism (the term idiopathic means that the cause is unknown), but more commonly today it is simply called Parkinson’s disease, to honor the physician who first described it.
What is PD?
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 thesubstania 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 the 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 simplylewy boy 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 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 no cure for PD (one can only cure a disease when one know 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.