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How is Parkinson’s diagnosed?
By Steven Frucht, MD and Robin Elliott
When patients are first diagnosed with Parkinson’s disease (PD), they often ask their doctor questions like these: “How can you be sure that I have PD? How long have I had PD, and how advanced is my illness? What will the future hold for me?”. The purpose of this brief article is to help patients understand how neurologists diagnose PD, how sure they can be of the diagnosis, and how certain specific tests can help in the diagnosis and management of patients with PD.
To this day, PD remains a clinical diagnosis that is it is based on the patient’s history and the signs that are present on neurologic examination. In the hands of a skilled movement disorder physician, this exam is extremely sensitive for signs of early PD, and it is usually possible for the neurologist to say whether parkinsonism is present or not. One of the most powerful – and simple – tests used in the examination is a measure known as the Unified Parkinson’s Disease Rating Scale (UPDRS).
The UPDRS consists of four parts. The first two parts are based on information provided by the patient regarding performance at home in a variety of daily activities (dressing, showering, bathing, walking, eating, etc.). The other two involve a careful examination by the neurologist. Among the questions the doctor is seeking to answer are the following: is the facial expression blunted? Is there tremor present at rest or when the arms are extended? Is there stiffness in the limbs or the neck? Is there slowing of movement of the hands or feet? Can the patient get up out of a chair easily? Does he or she walk with a normal stride, swinging the arms symmetrically? Is the patient’s balance normal? The questions may sound simple, but when the UPDRS is performed correctly, it is an exquisitely sensitive test for detecting early PD.
Sensitive, certainly, but not perfect. In cases where the doctor is unsure, some ancillary tests are available. One of these tests is performed in a motor physiology laboratory, such as the one that is directed by Dr. Seth Pullman at Columbia-Presbyterian Medical Center. By measuring the force and speed with which patients perform certain tasks, such as copying spirals or reaching for targets, a motor physiologist can detect and measure the extent of parkinsonism. These tests are very useful in confirming the diagnosis, and can also provide information on the efficacy of treatment.
An increasingly important area of diagnostic testing is neuroimaging. Over the past 15 years, imaging techniques have provided neurologists with a window through which they can directly measure the nerve cells that are affected in PD. While these techniques are not routinely available, they have contributed greatly to our understanding of how PD affects patients at different stages of life.
Here’s how they work: Most clinical signs of PD are caused by the loss of dopamine neurons, which are located in the section of the midbrain known as the substantia nigra. PET scanning – using 18-fluorodopa, a radioactively-labelled form of levodopa that is injected by an intravenous line into the patient -- is a technique that measures these neurons in patients. PET’s initials stand for “positron emission tomography,” a process whereby “positrons” (the energy given off by the radioactivity) are measured by a “tomogram”, which is nothing more than a routine CAT scan. Thus an 18-flurodopa PET scan is just like a regular CAT scan of the head, with one additional feature: injection of the radioactive tracer. The procedure lasts only about 30 minutes, uses very low levels of radioactivity, and poses virtually no long-term risk to patients.
18-flurodopa PET scanning is extremely sensitive to changes in the number of dopamine cells and all patients with clinical signs of PD will have an abnormal fluorodopa PET scan. Over the course of the disease, as the number of surviving dopamine neurons decreases, the imaging staff can reduce the intensity of the PET scan, thereby permitting finer measurement of the speed at which the disease has progressed.
Another technique that is used to measure dopamine status in patients with PD is called “Beta-CIT-SPECT”. This technique differs from fluorodopa PET in two respects: in the nature of the radioactive tracer (in this case, beta-CIT), and in the way in which the measuring device is calibrated.
How should fluorodopa PET scanning, or beta-CIT SPECT, be used in clinical practice? The answer is, not much. A major limitation of these techniques is their cost. Both scans are extremely expensive, running - anywhere from $2,500 to $6,000 – and they are often not covered by insurance companies which consider them experimental for the management of PD.
Whatever the reason, the bottom line of all this is that the procedures are not routinely available for patient care. It is also true that for most patients with newly diagnosed PD, the tests are not necessary. In the vast majority of cases, the UPDRS and the neurologic examination are more than sensitive enough to make the diagnosis, and necessary medication adjustments are prompted by changes in patients’ clinical profile. This means that the tests are almost never necessary in routine clinical practice.
Sometimes a doctor who is examining a patient for PD will see atypical clinical features that suggest an alternate diagnosis. In these cases, imaging studies -- particularly fluorodeoxyglucose PET scanning -- can be extremely helpful in confirming the doctor’s suspicions that the patient does not have PD at all.
What do we learn from all of this? For us, the most important single lesson is that it the key factor in diagnosing Parkinson’s is not the complexity or sophistication of the technology but the skill and specialization of the doctor. Parkinson’s diagnosis may be one of the most error-prone in medical care – some estimates are that 30 percent or more of patients are misdiagnosed, in one direction or the other – but the reason is to be found in the experience of the medical people, not in the tools they have at their disposal. To be a good diagnostician of Parkinson’s, a doctor needs to be able to see, and learn from, a sufficient number of patients. Patients and their families should be sure that the doctor they see has this kind of background. A good place to start is to see whether the doctor is a member of the Movement Disorders Society, a professional organization of neurologists and others who specialize in Parkinson’s and other movement disorders. Certainly there are many fine doctors who are not members of this society but the ones who ARE members you know have considerable expertise in the subject. If you’re in doubt, call the PDF at 1-800-457-6676 and they will be happy to give you some names.