Stages of PD

Staging is Not Important in Evaluating Parkinson’s Disease

By Joseph H Friedman, MD

Patients often ask what stage of PD that they are in. I then explain the following as to why that is not an important issue.

Staging in most diseases is important in predicting how long people will live or how well they can function. This is particularly important in cancer and heart disease. Different cancers have different systems for staging as experience has accumulated to distinguish how ominous it is to have cancer spread to local lymph nodes, or distant nodes, above the diaphragm, or below the diaphragm, in the bone marrow or not, etc. So stage 2b in one disease may have a very different prognosis than stage 2b in another form of cancer, but each will be associated with a certain chance of survival for a specified period.

This is not true for staging in PD. The staging system we use is based on a famous paper written by Margaret Hoehn and Melvin Yahr in 1967. Their paper was the first large study of the effect of LDopa on disease progression. In order to assess how the disease progressed, they had to develop a system to rate the severity. It wouldn’t do, for example, to say “mild,” “moderate,” or “severe,” as the readers would want to know what they meant by these terms.

In the Hoehn-Yahr (H-Y) staging system, stage 1.0 means that the PD is limited to one side of the body. Tremor, rigidity, reduced arm swing, and slowness are present only on one side. Stage 2.0 refers to problems affecting both sides, although one side may be only minimally involved. I should state that there are experts who think there is no such thing as stage 1.0, that everyone with involvement on one side has some deficit on the other, but that might be hard to see because there isn’t a normal side to compare with and because we know from autopsy evidence that PD always affects both sides.

In the original H-Y system there were no stages 1.5 and 2.5. These were added later as refinements. In stage 1.5, only one side is affected, but one can see symmetric problems on both sides such as reduced facial expression on both sides, stooped posture on both sides, or reduced arm swing on both
sides. In stage 2.5 both sides are involved plus there is a mild impairment of balance, but not loss of balance. To test for this, the patient is told that he will be pulled backward and to take a step back to try to prevent a fall. The patient is then pulled backward firmly. It is considered normal to take one or two steps, but if three or more are taken and balance is recovered, it is considered stage 2.5 (or 1.5 if there are no signs of PD on the better side).

Stage 3 refers to PD with impaired balance, defined by loss of balance when pulled backward so that the examiner must catch the patient to prevent a fall.

Stage 4 is defined differently in different places. In some places it is defined by the need for an assistive device or a person to help walk, whereas in others it refers to severe impairment but where some walking is possible.

Stage 5 means unable to walk.

The first problem with the H-Y staging is that it is based purely on mobility and takes no account of mental, behavioral or other non-motor problems. Since every study on health-related quality of life demonstrates that the most important determinants of quality of life in PD patients are non-motor, behavioral problems such as dementia, depression, fatigue, and sleep disorders, it may be irrelevant if the motor symptoms are mild but the patient is depressed and demented. His disease has severely altered his life, yet he may have stage 1.0, or seemingly mild disease.

The second problem has to do with the impact of the motor symptoms. A person may have stage 1.0, the lowest possible stage, with a small amount of tremor, a little slowness and reduced arm swing, but look and work normally; or the PD may be very severe on the one side so that one arm is almost useless but the other side is normal. If the affected side is non-dominant, for example the left side is affected in a right-handed person, the disease is annoying but may not interfere with work. The same stage, 1.0, affecting the right side may be completely debilitating. Yet, they are both stage 1.0

Unlike staging for cancer, higher stages may be less severe than lower stages. For example, a person who has minimal motor dysfunction but has it on both sides has stage 2.0, which might be far less severe than someone who has severe motor problems on only the dominant side. Similarly, someone with stage 3, meaning there is a balance problem, may have very mild motor dysfunction and have less
impairment than someone with stage 1.0.

One can easily imagine many scenarios where a lower stage is associated with more severe disease than a higher stage. And even if we look at scoring systems like the Unified Parkinson’s Disease Rating Scale, in which there is a point score each for tremor, rigidity, speech, slowness, etc, one sees the
same confounding problems. For example, we rate tremor in each limb and the chin, from 0, meaning not present, to 4, meaning severe, and similarly for speech. Imagine someone who scores a 5 because there is a very minimal tremor in each arm, leg and chin. Compare this to a person with no tremor but
speech which is totally incomprehensible, which would rate a 4. Thus, without seeing the actual patient, one would be misled to think that the person with a 5 was worse than the one with a 4, where the opposite is the case.

Severity of PD is currently not really measurable. We rate different aspects of PD differently and often use multiple different scales. It affects people in so many different ways that it defies methods for comparison, just as it has been impossible so far to measure what we mean when we say disease progression. We have good methods for measuring the motor symptoms of PD. We add points for tremor, stiffness, slowness, posture, walking, etc. and come up with a number, and that is how we currently test new treatments for PD.

Does the treatment reduce that number? Does it slow worsening of that number? We also have methods for rating the non-motor symptoms, like pain, fatigue, sleepiness, and methods for rating the impact of the motor symptoms, such as drooling, penmanship, speech, but there is no single score than can capture the real impact of the disease. How should one compare someone whose speech is unintelligible but able to do almost anything else, to someone who can communicate clearly but has severe tremors and needs a walker?

The H-Y scale is useful for looking at populations of PD patients but is not useful for assessing a single person. It helps us understand how various treatments alter the progression of motor problems in large groups. The severity of your own PD is really a matter of how severely it affects your life. A number can never capture this.


Dr. Friedman is a clinical professor, Department of Clinical Neurosciences, Brown University School of Medicine, Providence, R.I., and medical director of APDA’s Rhode Island Information & Referral Center in Warwick.

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