Parkinson’s disease (PD), or simply Parkinson’s, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. As the disease worsens non-motor symptoms become more common. The symptoms usually emerge slowly. Early in the disease the most obvious symptoms are shaking, rigidity, slowness of movement and difficulty with walking.
Thinking and behavioral problems may also occur. Dementia becomes common in the advanced stages of the disease. Depression and anxiety are also common, occurring in more than a third of people with PD. Other symptoms include sensory, sleep and emotional problems. The main motor symptoms are collectively called “parkinsonism”, or a “parkinsonian syndrome”.
The cause of Parkinson’s disease is unknown, but is believed to involve both genetic and environmental factors. Those with a family member affected are more likely to get the disease themselves.
There is also an increased risk in people exposed to certain pesticides and among those who have had prior head injuries, while there is a reduced risk in tobacco smokers and those who drink coffee or tea. The motor symptoms of the disease result from the death of cells in the substantia nigra, a region of the mid-brain. This results in not enough dopamine in this region of the brain.
The cause of this cell death is poorly understood, but it involves the build-up of proteins into Lewy bodies in the neurons. Diagnosis of typical cases is mainly based on symptoms, with tests such as neuro-imaging used to rule out other diseases.
There is no cure for Parkinson’s disease. Treatment aims to improve the symptoms. Initial treatment is typically with the anti-parkinson medication levodopa (L-DOPA), followed by dopamine agonists when levodopa becomes less effective. As the disease progresses and neurons continue to be lost, these medications become less effective while at the same time they produce a complication marked by involuntary writhing movements.
Diet and some forms of rehabilitation have shown some effectiveness at improving symptoms. Surgery to place micro-electrodes for deep brain stimulation has been used to reduce motor symptoms in severe cases where drugs are ineffective. Evidence for treatments for the non-movement-related symptoms of PD, such as sleep disturbances and emotional problems, is less strong.
In 2015, PD affected 6.2 million people and resulted in about 117,400 deaths globally. Parkinson’s disease typically occurs in people over the age of 60, of whom about one percent are affected. Males are more often affected than females at a ratio of around 3:2. When it is seen in people before the age of 50, it is called early-onset PD. The average life expectancy following diagnosis is between 7 and 15 years.
- Parkinson’s disease dementia starts as a movement disorder, but progresses to include dementia and changes in mood and behavior.
- The substantia nigra (SN) is located in the mid-brain that plays an important role in reward and movement.
- The mid-brain is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness) and temperature regulation.
- l-DOPA, also known as levodopa is an amino acid that is made and used as part of the normal biology of humans as well as some animals and plants.
- A micro-electrode is an electrode used in electro-physiology either for recording neural signals or for the electrical stimulation of nerve tissue.
Signs and symptoms
Four motor symptoms are considered cardinal in Parkinson’s Disease: tremor, slowness of movement (Bradykinesia), rigidity and postural instability.
- The most common presenting sign is a coarse slow tremor of the hand at rest which disappears during voluntary movement of the affected arm and in the deeper stages of sleep.
- Bradykinesia is the most handicapping symptom of Parkinson’s disease leading to difficulties with everyday tasks such as dressing, feeding, and bathing. It leads to particular difficulty in carrying out two independent motor activities at the same time.
- Rigidity is stiffness and resistance to limb movement caused by increased muscle tone, an excessive and continuous contraction of muscles.
- Postural instability is typical in the later stages of the disease, leading to impaired balance and frequent falls, and secondarily to bone fractures, loss of confidence and reduced mobility.
- Other recognized motor signs and symptoms include gait and posture disturbances such as rapid shuffling steps and a forward-flexed posture when walking with no flexed arm swing.
Exercise in middle age may reduce the risk of Parkinson’s disease later in life. Caffeine also appears protective with a greater decrease in risk occurring with a larger intake of caffeinated beverages such as coffee. People who smoke cigarettes or use smokeless tobacco are less likely than non-smokers to develop Parkinson’s Disease (PD), and the more they have used tobacco, the less likely they are to develop PD. It is not known what underlies this effect. Tobacco use may actually protect against PD, or it may be that an unknown factor both increases the risk of PD and causes an aversion to tobacco or makes it easier to stop using tobacco.
Antioxidants, such as vitamins C and E, have been proposed to protect against the disease, but results of studies have been contradictory and no positive effect has been proven. The results regarding fat and fatty acids have been contradictory, with various studies reporting protective effects, risk-increasing effects or no effects. There have been preliminary indications that the use of anti-inflammatory drugs and calcium channel blockers may be protective. A 2010 meta-analysis found that non-steroidal anti-inflammatory drugs (apart from aspirin), have been associated with at least a 15 percent (higher in long-term and regular users) reduction in the incidence of the development of Parkinson’s disease.