The rate of disease progression varies from person to person. The Hoehn and Yahr stages are commonly used to describe disease progression. According to this scheme the disease may be staged as follows:
- Stage Zero: No signs of disease.
- Stage One: PD symptoms on one side of the body only.
- Stage Two: PD symptoms on both sides of the body. No impairment of balance.
- Stage Three: Balance impairment. Mild to moderate disease. Physically independent.
- Stage Four: Severe disability, still able to walk or stand unassisted.
- Stage Five: Wheelchair bound or bedridden unless assisted.
The Hoehn and Yahr scale is a useful description of the broad stage of the disease. However, it is not based on underlying mechanisms of the disease, nor is it comprehensive enough as a research tool. A more comprehensive rating scale is used by most specialists in Parkinson's disease. This is the Unified Parkinson's Disease Rating Scale (UPDRS). This scale is widely used in clinical trials and is described on the WE MOVE organization's web site.
Classification by Clinical Stages
Another way of looking at disease progression is to classify the patient according to the response to medications.
Patient Newly Diagnosed with PD
At this stage a decision must be made whether or not to treat the patient with medications. If medical treatment is selected, the next decision is regarding the choice of specific medications (See section on medications). The patient should be screened for depression which is a common accompaniment of the physical symptoms. Lifestyle changes including exercise and nutrition should also be discussed.
Patient with Sstable Rsponse to Medications
At this stage, symptoms are markedly reduced without any evidence of breakthrough symptoms between doses. This "honeymoon phase" usually lasts from one to five years on carbidopa/levodopa (Sinemet). This phase may last longer in about 25% of patients. However, the most patients will develop motor fluctuations as described in the stages below. There is increasing evidence that using dopamine agonists instead of Sinemet for early disease may delay the development of motor fluctuations.
Patient with Predictable Wearing Off
At this stage, the patient begins to notice breakthrough symptoms towards the end of each dose. A dose which would previously last 6 to 8 hours now may last for 3 to 4 hours or even less. Patients alternate between an "on state" where their symptoms are well controlled, and an "off state" where symptoms are not masked by medication. The patient is forced to increase the frequency and/or strength of medications.
Adding COMT inhibitors such as entacapone (Comtan) to Sinemet may help reduce this wearing off phenomenon.
Patient with Unpredictable On-Off Fluctuations
At this stage, the breakthrough symptoms do not occur at predictable times at the end of dose but may occur at random. The off state may occur suddenly, sometimes within a few seconds. Stress and anxiety may provoke the onset of the off state. Patients tend to have more severe disability at this stage. Careful adjustments of medications by the neurologist are required for optimal control of symptoms. Surgical options become a consideration at this stage of the disease.
Patient with Dyskinesias
Patients may develop disabling involuntary movements at any stage of the disease. These movements called "dyskinesias" usually occur at the peak dose of medications. However, end of dose dyskinesias are may also occur. Reducing the amount of medication given with each dose but increasing frequency may help. Amantadine (Symmetrel) may be useful in reducing dyskinesias. Surgical options can be very useful in reducing dyskinesias.
Patient with a Yo-Yo Response
Patients may alternate between a severe off state and severe dyskinesias despite careful adjustments of medication dosages and frequencies. Reducing medications increases the off state disability, while increasing medications can lead to severe, disabling dyskinesias. Such patients often are best served by surgery.