Frequently Asked Questions (FAQ) about Parkinson's Disease
The diagnosis of Parkinson's disease (PD) is made on clinical grounds. The diagnostic test positron emission tomography (PET) can confirm or rule out the diagnosis of PD. We look at the diagnosis of PD as a three-step process.
The first step is to identify the presence of parkinsonism. Parkinsonism is a clinical syndrome defined by the presence of bradykinesia (slowness), rigidity (stiffness), resting tremor, and postural instability. By definition, the presence of 2 of the 4 cardinal manifestations of the syndrome is required to make the diagnosis of parkinsonism.
Once the diagnosis of parkinsonism is established, we proceed to step two, identification of the cause of parkinsonism. PD is responsible for 75% of cases of parkinsonism. Alternative causes include symptomatic, specifically, medication-induced, structural, and vascular lesions. There are also less common "Parkinson’s plus" syndromes that present as a combination of parkinsonism with other neurological features. The most common of them are progressive supranuclear palsy and multiple systems atrophy. Another common neurodegenerative condition, Alzheimer's disease, can have parkinsonism as part of its clinical picture. An entity of dementia with Lewy bodies is more and more recognized as an overlap syndrome of parkinsonism and cognitive dysfunction. In the majority of cases, a complete history and neurological examination will help to rule out alternative diagnoses. The correct diagnosis of PD is essential in counseling and educating the patient and family as well as in predicting successful response to treatment.
Step three is proving the clinical diagnosis by the presence of a positive response to treatment. Most experts in the field consider this step to be essential for an accurate diagnosis of PD. Parkinsonism caused by alternative neurodegenerative conditions usually does not respond to treatment, or the response is short-lived.
We always discuss the diagnosis of PD with the patient and their family. We explain to them that neuro-imaging (MRI or CAT scan) is not indicated unless there are some atypical features in the clinical exam. Thus, we save the patient the discomfort and expense of unnecessary studies.
The diagnosis of PD can be quite shocking to a patient, especially a younger person. We address the issue of the etiology of PD, explaining that it remains unknown. We specifically indicate that at the present time no genetic cause of PD has been identified. We explain that PD is caused by a deficiency of dopamine due to the degeneration of cells in the substantia nigra pars compacta (SNc). We discuss the progressive nature of the disease while at the same time explaining the multiple treatment alternatives and offering reassurance that the majority of patients are able to continue a full and productive life both occupationally and socially.
The first question to be answered is "Does this patient require pharmacological therapy?" Making the diagnosis of PD should not immediately lead to initiation of pharmacological therapy. Considering that all treatment options available do not readily affect the underlying pathophysiology of the disease, they should be used when symptoms negatively impact on the patient's functional level and not necessarily at the time of diagnosis. We always ask the patient how much their symptoms affect their daily activities (ADLs) both professionally and socially. If the patient is not functionally impaired, we delay symptomatic therapy aside from the use of selegiline. If the symptoms do impact on the patient's functional status, they certainly should be treated. The choice of a particular drug should be based on the prevailing symptom and factors such as age and accompanying problems.
No. The issue of possible levodopa neurotoxicity has been one of the most controversial questions in parkinsonology. There is no proven evidence of levodopa neurotoxicity in humans. The word "toxicity" in this setting is applied in the meaning of drug induced irreversible cell damage. There is some evidence that levodopa can be toxic to cells in culture. Animal data is controversial. Levodopa has never been shown to be neurotoxic in normal humans accidentally exposed to long-term levodopa therapy. There is no proven evidence of a neurotoxic effect in patients with PD. The presence of long-term drug induced complications is probably related to a number of factors including progression of the disease where, due to the declining number of dopaminergic cells in the substantia nigra, there is a decreased capacity to convert exogenous levodopa to dopamine and then release it in a steady fashion. Treatment with levodopa should not be withheld or postponed based on the risk of "neurotoxicity". However, levodopa should be used in the smallest therapeutically effective dose. Early use of dopamine agonists or combination therapy may allow the use of lower doses of levodopa which may translate into more sustained benefit from treatment.