As the cells degenerate, the production of dopamine is reduced. The greater a person’s age, the greater the chances of being diagnosed with Parkinson's disease (Fig. 1).
Dopamine is a neurotransmitter controlling movement, and when the concentration of dopamine declines, so does the concentration of other neurotransmitters, such as norephiniphrine and serotonin.
Risk Factors—Chances of Getting Parkinson's Disease
Aging is the major risk factor in Parkinson's disease (PD). In fact, the risk of being diagnosed with Parkinson's disease rises steeply after the age of 50. The lifetime risk of getting Parkinson's disease is slightly less than 1.3 %, and men are 1.5 times more likely to get Parkinson's in their lifetime than females.
From Figure 1 (further below), it could look as if the lifetime risk is larger than 1.3%, but it isn't, as many people die before the age of 80 years.
The mean age of diagnosis varies from study to study. According to the many studies listed below, the average age for time of diagnosis seems to be somewhere around 65.3 years old in the Western world, and women seem, on average, to be diagnosed one year later in their life than men.
The table below presents a compilation of studies from 1967-1999 where populations larger than 100,000 people were investigated. It seems as if the incidence of Parkinson's disease in China is significantly lower than in other countries. As the life expectancy in China is 73years on average, the low incidence of PD in China might be due to inadequate medical records at the time the study was made (1991). Recent evidence suggests that the incidence of PD in China is at the same level as in other parts of the developed world.
The most common drug used to help Parkinson's patients is L-dopa. L-dopa is administered together with another medication. This is the medicine given to most patients, often three years after diagnosis. Patients getting L-dopa will quickly experience significant improvements in their condition. Their fatigue diminishes, and the problems they had with initiating movements is reduced significantly. After a longer period with L-dopa, the medication will often be shifted to something better at handling symptoms of patients diagnosed eight to ten years earlier. Wii (yes, the video game console) is used to help PD patients improve their motor skills.
Non-motor symptoms also have a great impact on the quality of life of Parkinson's disease patients. Non-motor symptoms include neuropsychiatric effects, autonomic nerve system irregularities, gastrointestinal disturbances, sleep problems, fatigue problems, and anxiety.
However, because these symptoms are not easily seen, they are sometimes not considered an important component of PD, as are motor symptoms. In fact, the bulk of clinical attention goes into motor symptoms and not non-motor symptoms.
The motor symptoms mainly arise because of the lack of dopamine-producing cells in the substantia nigra, whereas the non-motor symptoms arise because of degeneration in parts of the brain outside the substantia nigra, as well as cortical degeneration in later stages of the disease. Secondly, non-motor symptoms can be exacerbated by PD medicine.
That is, especially cognitive functions can be impaired by dopamine antagonists and levadoda.
The treatment of motor symptoms is already very effective, but depression and anxiety can be just as debilitating as motor symptoms. Psychosis and depression can actually be treated quite effectively, which is often overlooked by practitioners for Parkinson's patients.
Numerous studies have shown that although motor disability is the key driver to overall well being in PD patients, other features, such as depression and cognitive impairment, are also important contributors to impaired quality of life.
Non-motor symptoms can be divided into four types:
Cognitive impairment, such as PD dementia
Psychosis, including hallucinations
There is still a need for much better medication against cognitive impairment in PD.
For both depression and anxiety, there are very good treatments.
The depression seen in Parkinson's disease patients is, however, not entirely the same as depression seen in patients without neurological disorders. There are still a lot of unanswered questions about PD depression that need to be resolved for an optimal treatment of depression in Parkinson's disease patients.
Psychosis, which is a late manifestation in Parkinson's disease, can also be effectively reduced by medication.
Sensory abnormalities are very common too. Patients often experience lower pain threshold values, and some patients also experience painful cramps.
Pain issues are more than just a nuisance, as 20 to 40 percent of all Parkinson's disease patients complain about pain. The best way to reduce pain is exercise and physical therapy. As the pain is really chronic in nature, and it can be reduced by means other than medication, it is probably a viable idea to avoid the use of medicine against pain for as long as possible.
Another sensory issue often experienced is a decreased sense of smell. It causes very little disability in patients, but it is seen in almost all patients. A few patients even experience a reduction in color vision.
Daytime drowsiness and sleep fragmentation are the two most common sleep disorders. Sleep fragmentation is when people fall asleep and wake up in the middle of the night and cannot fall asleep again.
Drowsiness can be reduced by naps during the day. Daytime drowsiness can be an effect of some of the medicine against motor symptoms, and sometimes small adjustments can reduce the problem with drowsiness.
Parkinson's Disease Symptoms
The onset of Parkinson's disease is gradual, and the first symptoms may well be misinterpreted for a long time. Stiffness and fatigue are two early symptoms that might as well be a symptom of age. Stiff or slow facial expressions may be another symptom that goes unnoticed for a period of time.
Early symptoms are often ascribed to old age, and there is often a period of two to three years from the first symptoms to diagnosis.
The diagnosis is made by a neurologist that will subject the patient to one or more tests that should reveal if the patient has Parkinson's disease or not.
When the patient has been diagnosed, his friends and colleagues will often look back at the symptoms and attribute them to Parkinson's disease.
Accuracy of Diagnosis
Only a few studies have investigated the accuracy of clinical diagnosis of Parkinons's disease. However, two studies have estimated the accuracy of diagnosis to be somewhere around 80%16,17. The misdiagnosis is due to the fact that some symptoms from other diseases, such as Multiple System Atrophy, Alzheimer's, progressive supranuclear palsy, and cerebrovascular pathology. Therefore, statistics about how old people were when they were diagnosed with Parkinson's disease should always be taken with a grain of salt. Secondly, when studies from different countries are compared, one has to take into account that some countries might use criteria for diagnosis slightly different from those of other countries. Furthermore, doctors in some countries might be better at diagnosing PD than those in other countries.
Parkinson's disease patients experience a number of symptoms, some of which are common in all patients. These are, in short, the TRAP symptoms:
• Tremble involuntarily (Tremor)
• Rigid and stiff muscles (Rigidity)
• Loss of ability to make voluntary movements (Akinesia)
• Difficulty in maintaining balance (Postural instability)
Many of these symptoms are characteristic of other diseases as well, and sometimes it is difficult to give a diagnosis of Parkinson's disease just based on the TRAP symptoms.
The TRAP symptoms become more pronounced as the disease progresses. When the first symptoms become visible, it is estimated that 80 percent of all dopamine-producing cells in the substantia nigra are dead. A person suffering from the TRAP symptoms is said to suffer from parkinsonism, but the same symptoms may be visible in a person suffering from a number of other diseases, strokes, and side effects from certain type of medications. The most common diseases that can be mistaken for Parkinson’s disease are:
Progressive Supranuclear Palsy (PSP)
Multiple System Atrophy (MSA)
When people show signs of parkinsonism following a stroke, it is most often because the substantia nigra has been damaged. Twenty percent of cases of parkinsonism are due to other reasons than Parkinson’s disease.
I've listed "things" related to Parkinson's disease as either being used for a) diagnosis of Parkinson's disease, b) criteria that can help exclude Parkinson's disease, and c) criteria that support the diagnosis of Parkinson's disease.
The three categories of symptoms and causes that either increase or decrease the chance that the patient has Parkinson's disease are:
Parkinson's Disease, Almost Certain
Bradykinesia (slow movements, difficulty in initiating movements) in combination with:
Rest tremor with a frequency of 4-6 hertz
Instability that is not due to visual impairment or balance problems caused by other dysfunctions
Excluding Parkinson's disease
Repeated strokes before suspicion of Parkinson's disease
Many head injuries in medical record
History of brain inflammation (encephalitis); meningitis—a very common form of brain inflammation is meningoencephalitis
Rotating eyeballs caused by certain types of medicine
Already in treatment with neuroleptics
Symptoms on one side of the body only
Early dementia with disturbance of language
Exposure to a neurotoxin called MPTP
Negative response to large doses of L-dopamine
If the first step is negative and the second step does not indicate it is not PD, the neurologist will begin seeing if anything else supports the diagnosis of Parkinson's disease:
The brady kinesia started in one side of the body only
The patient trembles (tremor) while at rest
The condition has progressed over a longer period of time
Excellent response to large doses of L-dopa
Recurring visual hallucinations
Reduced ability to smell odors
Parkinson's Disease Statistics
Fig. 1: Chance of getting Parkinson's disease. Data from Meta 1 (table further down)
Parkinson's Disease Statistics
The table below is divided into age groups so that the incidence (the number of people getting Parkinson's disease within one year out of a population of 100,000) is listed for each age group. The age groups listed are for a) people in their thirties, b) in their forties, c) fifties, d) sixties, e) seventies, and f) an age group for people older than 79. The table also lists the overall incidence for the total population, the mean age of diagnosis, and the mean age of diagnosis for both men and women.
The data below are from studies where either a subset of a population was studied or case stories of many people were studied. There might be both advantages and disadvantages to using both methods.
|Pop size||Country||30-39||40-49||50-59||60-69||70-79||80+||All||Mean Age||Female||Male||Study|
|META 1||Weighted 1||0.66||2.8||18.3||52.4||80.1||60.1||12.6|
|META 2||Weighted 2||65.3|
|META 3||Weighted 3||64.6||63.4|
META 1 consists of all those studies where the age-specific incidence is listed, except for the one from China. These META 1 data are compiled of data from: Iceland, Italy, Finland, Poland, Sweden, USA, Spain, and the United Kingdom (UK). Data are weighted so that the study from Poland counts approximately 4.37 times as much (1,308,000/298,985) as the study from Sweden.
META 2 consists of all the studies above where an average age of diagnosis is available, except for China, which is a special case due to life expectancy, lifestyle, etc. The countries are: Iceland, Italy, Finland, Denmark, Japan (x2), Poland, Sweden, United Kingdom, USA, and Spain.
META 3 is a weighted average of all those studies where an average age of diagnoses was found for both males and females. Both numbers are lower than the overall average age. This is because some of the studies showing a high age of diagnosis are not included in the META 3 subset.
Parkinson's is a progressive brady kinetic disorder; meaning that the patient's ability to start and continue a movement is slowly impaired during the development of the disease. Fortunately, the disease progresses slowly, in part thanks to modern medications.
According to Hughes et al. (1992)19, 60-70 % of all cases of Parkinson's is idiopathic, that is, the cause is unknown. The remainder of cases, 30-40%, can be attributed to several other factors, such as drugs that can cause parkinsonism. MPTP is one of these drugs, and many naturally occurring drugs, that are not legal, can have the same effects as MPTP.
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