There is no test to diagnose Parkinson’s Disease
Although Parkinson’s disease is a specific, well defined disease that can be reliably diagnosed at autopsy, it is defined in life by clinical criteria. This means that the diagnosis rests entirely on the information (history) that the patient provides plus the physical examination. There is no test to diagnose PD. When a doctor orders a test when evaluating a patient who he thinks has PD, the test is really being obtained to make sure that there isn’t some other disorder that might look like PD. When I am convinced that a patient has Parkinson’s Disease I order no tests at all. No CAT scan, no MRI, no EEG, no spinal tap, no blood tests. Nothing. The reason is that if any of these tests was to show an abnormality, it would mean to me that the patient had Parkinson’s Disease plus some other disorder that has nothing to do with why the patient was seeing me in the first place. Generally I’d rather not know.
Parkinson’s is easily identified by a pathologist, but is difficult to diagnose for a clinician
When I state that Parkinson’s Disease is “well defined,” I mean that the pathologist, looking at slides of the brain under a microscope, can say, knowing nothing about the patient, that the person had PD. Parkinson’s Disease causes certain, easy to detect changes that are seen under the microscope. This, of course, requires that the person is dead, which isn’t much use to that particular person or his family. The absence of a reliable test, in life, means then that there is room for mistakes. And, in fact, we make a fair number of mistakes, and I’ll discuss below the types of cases in which we are most likely to make mistakes. Unfortunately, we are never in the position of being 100% certain that we’ve diagnosed someone correctly, until the autopsy.
How do we diagnose PD?
We look for certain “cardinal” or core features on the examination, plus a supportive history. For example, if a patient has recently been taking medications that can make someone look like they have PD, then the doctor would say, “You look like you may have PD, but this medication you’ve been taking may be the cause, so I’m not sure if you really have PD, or if the problems are entirely due to the medications.” Parkinson’s Disease is slow in onset, so if the patient said that she woke up one morning with tremors and a shuffling walk, but had been playing competitive tennis the evening before, we’d think that she more likely had a brain infection or had taken a medication with bad side effects. The history generally is of slowly progressive changes, developing over months, of intermittent tremors, usually in the hands or jaw, slowing down in general, difficulty getting out of a car seat or low, soft sofa, softening of the voice, smallness and slowing of handwriting, change in posture and facial expression. Very often something is only noticed on a particular day, but friends and family will generally report that although they didn’t notice particular changes, now that they know what to look for, the changes began months or even years before.
On examination we look for: tremor at rest, rigidity, slowness and loss of spontaneous movement, stooped posture and a characteristic way of walking.
Tremor: The tremor of Parkinson’s Disease is primarily at rest. This means that the tremor goes away when the limb is moving but returns when the limb relaxes completely. The tremor is usually asymmetric, affecting one side more than the other, or even affecting only one side. The fingers and hands are the most common body parts to be affected. The jaw is the next most commonly affected area. The legs and feet may also be affected, but less so. Virtually any body part may be affected, such as the tongue, the eyebrow, the lips. The tremor usually disappears during sleep. It increases during periods of stress and excitement, after exercise and in the cold. The tremor may be present all the time, or only very occasionally. It may sometimes affect one hand and sometimes both. During times of relaxation it may completely disappear. It always disappears when the limb is moving.
Sometimes patients will describe having a tremor at home, but not have it in the office. This is uncommon, but does occur. In such circumstances the doctor cannot rely on the patient’s report because the nature of the tremor is important, and not all tremors are due to PD.
Rigidity: this means stiffness. Patients with Parkinson’s Disease have some degree of stiffness in their joints. It is most common in the wrists and neck, but may be present everywhere. The patient may feel stiff, but not always. The doctor tests for stiffness by having the patient relax while the patient moves the various limbs to test for stiffness in the wrists, elbows, fingers, neck, legs. A normal person’s joints move like well oiled machine parts, whereas someone with Parkinson’s Disease will have a resistance to the doctor’s moving the limb, even though the person is relaxed. This resistance often, although not always, has a ratchety quality to it, called “cogwheel rigidity” because the movement feels like a cogged wheel moving.
Slowness, or “akinesia and bradykinesia.” Akinesia means “absence of movement and refers to the absence or reduction of normal spontaneous activity. Parkinson’s Disease patients are like statues. They tend to not move. They blink less than others. They swallow less. They have fewer movements like touching their face, scratching their nose, shifting positions in their chair, than normal people have. This is one of the causes for the “staring” expression and the “masked facial expression” of Parkinson’s Disease patients. It is also the cause for drooling (inadequate swallowing). Bradykinesia refers to slowness of movement, and is one of the main causes of disability in PD. Parkinson’s Disease patients move slower than others. They have reduced dexterity, particularly in their fingers so it takes a long time to button, zipper, manipulate small objects, put a screw into the wall, get money out of a wallet, etc. As one of my patients described it, “My left hand is fine, but I have to tell my right hand what to do. That slows me down a lot.” Patients sometimes have to consciously will an action that used to happen automatically, without thinking. If you had to “tell” your hand what to do to comb your hair, and guide each of its movements, it would take a lot longer than it should. This is what happens in PD. This also keeps Parkinson’s Disease patients from being able to do two things at the same time, another source of slowness.
Gait and posture: gait refers to how you walk. Parkinson’s Disease patients tend to become stooped. When they walk they don’t swing their arms, or swing them less than normal. They tend to walk with their foot hitting the ground flatly, rather than having their heel hit the ground first. The distance between the feet, as they take steps, tends to decrease, and the speed of walking diminishes as well. The heel may scuff the floor. When they turn, they tend to take a few steps rather than pivoting, that is, rotating on one foot.
Balance is impaired so that when knocked off balance, the Parkinson’s Disease patient may take several steps to keep from falling, or simply lose balance and fall, if not caught. The standard exam for Parkinson’s Disease has the patient pulled from behind for a balance check. The doctor is prepared to catch the patient.
Other features that are common in Parkinson’s Disease but are not considered “core” or “cardinal” features are: changes in voice, penmanship, sleep. The voice may become soft. Many patients develop a stutter, or develop an increased rate of speaking, despite having difficulty being understood. Penmanship, in addition to becoming slow and sometimes shaky, also becomes small. There are many sleep problems that develop in PD, but the one that is most indicative of a diagnosis of Parkinson’s Disease is “REM sleep disorder,” a condition in which patients may act out their dreams, kicking, punching, yelling while asleep.
In thinking about the above, it is important to keep in mind one very important underlying principle of brain function. Even though the brain looks pretty much the same from one part to another, each part has a particular function, so that if you damage a particular location in the brain, it will cause a very specific change in the person’s function. It doesn’t matter how that part of the brain is damaged, whether from a stroke, a tumor, a bullet wound or an infection.
This is one of the reasons we can’t always be sure that the diagnosis is PD. We can state that the particular part of the brain that is damaged in Parkinson’s Disease is affected, but we may be wrong about the process that is the cause. There are several different disorders that look very much like PD. Early on it may be impossible to tell if a patient has Parkinson’s Disease or some closely related disorder. This is especially true in elderly patients, since many of the normal changes that occur with age, may look like PD.