What Is Parkinson’s Disease?

What Is Parkinson’s Disease?

Parkinson’s disease (PD) is a long-term disorder involving degeneration of the central nervous system. The disease primarily impacts the motor system, which is responsible for our movements.

The symptoms of PD typically manifest themselves slowly. Non-motor symptoms usually become more common as PD progresses.

The primary early symptoms of PD include rigidity, tremors, problems walking, and slow movements. The disease also frequently leads to behavioral and cognitive issues such as apathy, anxiety, and depression. Dementia is frequently seen in those with advanced PD. PD can also cause issues with sensory systems and sleep.

PD’s motor symptoms are caused by cell death in a part of the brain known as the substantia nigra. The death of these cells leads to a deficit in dopamine, which is critical to motor system function. This cell death involves misfolded proteins building up into Lewy bodies in neurons.

Environmental and inherited factors are believed to play roles in the development of PD. Those with family members who have PD have a higher risk of developing the disease, and some genes are known to be risk factors. Other risk factors include pesticides and head injuries. Tobacco, tea, and coffee reduce the risk of PD.

Diagnosing Parkinson’s Disease

PD diagnosis usually focuses on symptoms—primarily motor symptoms. Other diseases can be ruled out using tests such as magnetic resonance imaging or DaT scans. The disease is typically seen in people over age 60. About one percent of people this age have PD.

Males develop PD more commonly than females. There are about three men with PD to every two women. PD that develops before age 50 is known as early-onset PD. 6.2 million people had PD in 2015. The disease resulted in around 117,400 deaths that year. The average post-diagnosis life expectancy for the disease is around seven to 15 years.

There is no known cure for PD. Treatments only attempt to reduce symptoms. The disease is usually initially treated with L-DOPA, dopamine agonists, or MAO-B inhibitors. These medications wane in effectiveness as the disease gets worse and produce involuntary muscle movements as a side effect. These medications may be combined and their doses increased when this occurs.

Some types of rehabilitation, as well as diet, have been found to be effective in improving the symptoms of PD. Severe cases where medication has been ineffective have been treated with surgery, which places microelectrodes in the brain for deep brain stimulation.

PD is named after the English doctor, James Parkinson. Parkinson published the first detailed description of PD in 1817. Famous people with PD include boxer Muhammad Ali, actor Michael J. Fox, actor Alan Alda, Olympic cyclist Davis Phinney, and comedian Billy Connolly.

Signs and Symptoms of Parkinson’s Disease

The primary signs of PD are:

  • Tremor
  • Bradykinesia (slowness of movement)
  • Rigidity
  • Postural instability


The most commonly seen sign of PD is a slow, coarse tremor of the hand while it is resting. This tremor disappears when the arm is being voluntarily moved, and during deep sleep. This tremor usually only appears in one hand, but will eventually affect both hands when the disease gets worse.

The frequency of this tremor is typically between four and six cycles per second. “Pill-rolling,” a movement where the thumb and index finger touch and move circularly together, is often seen in PD tremors.


Every PD case involves bradykinesia. This is because motor planning of movement initiation is disturbed. This slowness of movement causes problems with every stage of the process of moving, including planning, initiating, and executing movements.

Bradykinesia is the symptom that causes the largest handicap in those with PD. It interferes with everyday activities such as bathing, feeding, and dressing. It can make executing two movements at once especially difficult, and it can be exacerbated by concurrent illness or emotional stress.

Oddly enough, those with PD can often climb stairs or ride a bicycle more easily than they can walk on a level surface. Bradykinesia is diagnosed by having patients do repetitive movements with their feet and fingers.


Rigidity is resistance to limb movement and stiffness. It is caused by a continuous and excessive contraction of muscles. This rigidity can be uniform or irregular. Uniform rigidity in those with PD is known as “lead-pipe rigidity.” Irregular rigidity in those with PD is known as “cogwheel rigidity.”

Rigidity often leads to joint pain. Rigidity typically affects the neck and shoulder muscles first, and is asymmetrical, in PD’s early stages. Rigidity tends to later affect the muscles of extremities and the face, then the entire body, as the disease progresses, reducing the ability to move.

Postural Instability

Postural instability is common in the later stages of PD. It leads to frequent falls and impaired balance, which lead to reduced mobility, loss of confidence, and bone fractures. Instability is often not seen in those with early-stage PD, especially in younger people.

Up to 40 percent of those with PD may experience falls. About 10 percent of those with PD fall every week. Falls become more common as the severity of PD increases.

What Is Parkinson’s Disease?

Other motor symptoms of PD include:

  • Rapid shuffling steps
  • Walking with a forward-flexed posture and no flexed arm swing
  • Freezing of gait
  • Slurred, monotonous, quiet voice
  • A mask-like facial expression
  • Handwriting which becomes progressively smaller

Neuropsychiatric Disturbances

Numerous neuropsychiatric disturbances can be caused by PD, including thought, behavior, mood, and cognition disorders. These disturbances can occur during early-stage PD and get worse as the disease progresses.

Executive dysfunction, which involves issues with cognitive flexibility, planning, rule acquisition, abstract thinking, initiating appropriate actions, inhibiting inappropriate actions, control of attention, and working memory, is the most common cognitive deficit.

Other cognitive issues include impaired recall, slowed cognitive processing speed, and impaired estimation and perception of time. PD also involves visuospatial issues. These issues are often seen when those with PD perform facial recognition tests and tests regarding their perception of drawn lines’ orientation.

Those with PD face two to six times the risk of developing dementia. Up to 78 percent of those with PD have dementia. Dementia prevalence increases with age. Dementia leads to a reduced quality of life in those with PD and their caregivers, a higher chance of needing nursing home care, and increased mortality.

PD medication, especially orally active dopamine agonists, can lead to impulse-control disorders such as compulsive sexual behavior, pathological gambling, compulsive shopping, and binge eating. PD medication can also cause punding, which involves stereotyped, aimless, repetitive, complicated behaviors occurring for multiple hours.

Psychosis occurs in 26 to 83 percent of those with PD. About half of people with PD experience delusions or hallucinations, which can be a sign of dementia. Minor or vivid hallucinations can occur, as can paranoid ideation. Psychosis, delusions, and delirium are recognized complications of PD medication, but it is also thought that psychosis in PD can be caused by changes in neurotransmitters and underlying brain pathology.

Anxiety, Apathy, and Depression

Anxiety, apathy, and depression are the most commonly seen mood difficulties in those with PD. About 20 to 35 percent of those with PD have depression, which can appear during any stage of PD. It can be difficult to diagnose since its symptoms, such as problems concentrating, insomnia, and fatigue, can also be symptoms of PD.

Depression in those with PD can be caused by changes in and imbalance in serotonin, dopamine, and noradrenergic hormones. The impairment in function caused by PD can also lead to depression, which includes symptoms such as sadness, loss of interest, feelings of helplessness and hopelessness, guilt, and suicidal ideation.

About 30 to 40 percent of those with PD have anxiety. Those with PD suffer from panic attacks more commonly than those in the general population. Anxiety in those with PD may be caused by abnormal gamma-aminobutyric acid levels, as well as fear or embarrassment about the disease or its symptoms.

About 16 to 40 percent of those with PD experience apathy, or a loss of motivation and a reduced ability to experience pleasure.

Many with PD experience sleep disorders, which can be made worse by medications. Those with PD may experience daytime drowsiness, insomnia, or disturbances in REM sleep. Those with PD may experience REM behavior disorder, which causes them to act out their dreams, sometimes injuring themselves or their sleeping partner. This can occur years before other symptoms of PD manifest themselves.

Those with PD may experience low blood pressure upon standing, excessive sweating, oily skin, altered sexual function, urinary incontinence, impaired stomach emptying, constipation, an impaired sense of smell, pain, tingling, numbness, and disturbed vision.

Causes of Parkinson’s Disease

The most frequently replicated relationships involving the development of PD are an increased risk in people exposed to pesticides, such as paraquat, and a reduced risk in smokers.

Paraquat and Parkinson’s Disease

What Is Parkinson’s Disease?

Numerous studies, including studies from 2011, 2013, and 2018, have linked the herbicide paraquat with PD.

While elevated rates of PD are seen in farm workers and paraquat applicators, those who live near agricultural fields where paraquat is sprayed also see elevated rates of PD.

The motor symptoms of PD are caused by the death of dopaminergic neurons, which produce dopamine. Dopamine is critical to motor system function.

It appears that paraquat, once it enters the human body, is able to cross the blood-brain barrier. Once inside the brain, it appears that paraquat begins to undergo a looping, never-ending chain reaction which repeatedly kills dopaminergic neurons for the rest of a person’s life.

It appears that paraquat kills dopaminergic neurons due to its tendency to undergo redox cycling. Paraquat is a strong oxidant that readily undergoes redox cycling in the presence of oxygen, which is very plentiful in living cells. The redox properties of paraquat have been known since at least the 1930s, and it has been known since at least the 1960s that its redox properties make it toxic to plants and animals.

California law allows for those who have been injured by a product to recover damages in a lawsuit if the manufacturer of the product knew or should have known that its product was dangerous yet failed to warn about the danger. Countless products containing paraquat have been sold without labeling warning about an increased risk of PD.

If you or a loved one has developed PD after being exposed to the herbicide paraquat, you may be eligible for financial compensation in a paraquat lawsuit. Contact us today for a free consultation, and click here for more about the connection between paraquat and PD. We are contingency fee lawyers, which means we don’t charge a fee unless and until we win your case.

Genetic Causes

About 15 percent of those with PD have a first-degree relative with PD. About five to 10 percent of those with PD have a form of PD caused by a genetic mutation. Those with these gene mutations may not develop PD.

At least 20 genetic mutations have been implicated in PD development.

Around five percent of those with PD have a mutation in the GBA1 gene, a mutation that is present in less than one percent of those without PD. Those with GBA1 mutations are twenty to thirty times more likely to develop PD. PD associated with GBA1 mutations typically has an earlier age of onset and a more rapid motor and cognitive decline.

Non-Genetic Causes

In addition to paraquat, other non-genetic factors which have been linked with PD include pesticides such as maneb, as well as head injuries. Toxins such as carbon disulfide and manganese have been linked with PD.

Parkinson’s symptoms can be caused by medications such as phenothiazines, butyrophenones, tetrabenazine, and metoclopramide. However, drug-induced PD symptoms can usually be reversed by no longer taking the offending medication. MPTP is a drug known to cause irreversible PD symptoms.

Low urate concentrations in the blood have been linked with PD.

Metabolic derangement and infections have been linked with PD symptoms.


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