Dr. Joseph Jankovic 00:00:05
We know that Parkinson's disease is not just a single entity. There are many different subtypes of Parkinson's disease. At least 30 years ago, we described two major subtypes of Parkinson's disease. One is referred to as the tremor-dominant form of Parkinson's disease, which represents about 75% of all patients with Parkinson's disease. And the second subtype is what we refer to as PIGD, postural instability gait difficulty form of Parkinson's.
The first subtype, the tremor-dominant form of Parkinson's disease, often starts at a relatively younger age, somewhere between the ages of 45 and 55. The onset usually is tremor, sort of a rest tremor, usually in the hand, and then it spreads to the opposite side. It may involve other parts of the body such as the lips, chin, jaw and legs. But it never involves the head, so if one sees an individual with oscillation of their head like "no, no, no" or "yes, yes, yes," that individual almost certainly does not have Parkinson's disease, but has another condition, namely essential tremor, which is frequently confused with Parkinson's disease.
Now, for a long time, it was thought that essential tremor and Parkinson's disease are totally distinct disorders. And this is probably true still for the majority of patients with Parkinson's disease and essential tremor. But we have accumulated some evidence over the last two or three decades to indicate that there is a subtype of patients with essential tremor that may evolve into this tremor-dominant form of Parkinson's disease.
Some patients with essential tremor are at an increased risk for developing Parkinson's disease. So this is the tremor-dominant form of Parkinson's disease, the most common form of Parkinson's disease. Usually it has a much more favorable prognosis than the second subtype of Parkinson's disease, the PIGD form of Parkinson's disease. In this form of Parkinson's disease, the PIGD, or postural instability gait difficulty form of Parkinson's, patients often start with a shuffling gait with some difficulty with their balance, with a tendency to fall either forward or backward. They develop falls early in the course of the disease.
Dr. Joseph Jankovic 00:02:40
The natural course of progression in the PIGD form of Parkinson's disease is much more rapid than in the tremor-dominant form, so the prognosis is less favorable. And they do not respond as well to anti-Parkinson medications such as levodopa. So when I see patients with Parkinson's disease, if they had the tremor-dominant form of Parkinson's disease, I may tell them, "Well, the bad news is that you have Parkinson's disease, but the good news is that you have the best kind of Parkinson's disease, the kind of Parkinson's that generally has a good prognosis."
Now, in addition to the tremor form of Parkinson's disease and the PIGD form of Parkinson's disease, we often subdivide Parkinson's disease according to the age of onset. So there could be a juvenile form of Parkinson's disease starting in childhood; it's extremely rare, but it does occur. Then there's a young-onset form of Parkinson's disease that may start in the 20s or 30s. These patients often respond very well to levodopa but are much more vulnerable to the side effects of levodopa, such as dyskinesias, the twisting, jerking type involuntary movements. And that is a characteristic feature of young-onset Parkinson's disease.
And then there is late-onset Parkinson's disease, which tends to be more of the PIGD form of Parkinson's. These patients tend to develop the gait difficulty and balance problem early on, and they may often develop cognitive decline early on, and dementia becomes the dominant feature in the more advanced stages of the disease. Speaking of stages of the disease, we divide the natural course of progression of Parkinson's disease into the five stages, the so-called Hoehn-Yahr stages. Stage one represents chiefly unilateral, one-sided symptoms such as tremor. Stage two means that the symptoms occur bilaterally, on both sides.
Stage three means that the patient begins to develop some difficulties with their balance, but they are still able to ambulate without assistance. Stage four means they require assistance with ambulation. And stage five usually means that the patients are wheelchair-bound or bedridden. So these are the five stages of Parkinson's disease. Our goal, of course, is to maintain the patient in the earliest stages of the disease as possible with appropriate treatment.