What is Parkinson’s disease?

Parkinson’s disease¹ (PD) is a nervous system (brain) disorder that primarily affects the regions of the brain that control balance and movement. PD is a progressive disease, meaning that its symptoms appear gradually and worsen over time. It is characterized by² its effect on motor functions of the body and presents in the form of tremors (shaking), muscle stiffness or rigidity, and slow movement.

How common is Parkinson’s disease?

Parkinson’s disease affects 10 million people worldwide³, and more than 1 million people in the United States alone. Approximately 60,000 new cases⁴ are diagnosed each year in the U.S. The frequency of Parkinson’s disease in the United States is 13 cases per 100,000 people⁵.

Researchers and healthcare providers expect more people to be diagnosed with Parkinson’s disease in future decades as the average life expectancy continues to increase, as the risk of developing PD increases with age.

Parkinson’s disease causes

Nerve cells in the brain (called neurons) produce chemicals called neurotransmitters. These neurotransmitters act as chemical messengers that control certain functions and behaviors in the body.

Parkinson’s disease is caused by⁶ the impairment or death of neurons. This is what leads to the physical symptoms that are seen as the disease progresses.

The brain chemical dopamine is the most closely associated with PD. When the nerve cells that produce dopamine die, the movement issues characteristic of PD arise. These include difficulty balancing and walking, coordination problems, muscle stiffness, and uncontrolled shaking.

Studies have suggested that another important neurotransmitter, norepinephrine, is often significantly decreased in people with Parkinson’s. This neurotransmitter plays an important role in the function of the sympathetic nervous system, which controls unconscious bodily functions (such as heart rate, respiratory rate, and blood pressure).

Scientists and healthcare providers do not know for sure why some people develop Parkinson’s disease and some do not. Because the exact origin of the disease is unknown, methods of preventing Parkinson’s are also unknown at this time.

Risk factors for Parkinson’s disease

Some environmental and physical factors⁷ may increase your risk of developing Parkinson’s disease, including:

• Age: While some people develop early-onset Parkinson’s disease (which is diagnosed in people younger than 50 years of age), the risk of developing the disease increases with age. 90–95% of people with Parkinson’s disease⁸ are diagnosed with the condition after the age of 60.

• Gender: Parkinson’s disease affects 50% more men than women.
• Genetics: While most cases of PD are unrelated to familial inheritance, some people who are diagnosed with Parkinson’s disease have an inheritance pattern involving certain altered genes, which could increase their risk of developing the disease.
• Environmental Causes: Several studies have confirmed a link between Parkinson’s disease and chemical exposure from pesticides and herbicides, in addition to metal and other organic pollutants.
• Head injury: Repeated physical trauma to the head and brain can increase your risk of developing Parkinson’s, as well as other conditions that may cause the symptoms of dementia.

Parkinson’s disease symptoms

The signs and symptoms⁹ of Parkinson’s disease vary from person to person. Some people experience a few of these symptoms, while others experience most or all of the following:

• Tremors (trembling or shaking)
• Bradykinesia (slowed movement)
• Rigid or stiff muscles
• Impaired posture and balance
• Decreased ability to perform automatic movements
• Changes in speech and/or writing patterns
• Trouble chewing and/or swallowing
• Memory loss
• Trouble sleeping or insomnia
• Anxiety or depression
• Sexual dysfunction (such as erectile dysfunction, or ED)
• Restless legs
• Muscle cramps

The presence of one (or even a few) of any of these symptoms does not definitively indicate Parkinson’s disease. If you or a loved one shows any of the signs or symptoms of PD, talk to a healthcare provider to determine the right diagnosis and treatment.

Early signs of Parkinson’s disease

Because Parkinson’s is a progressive disease, it presents in its early stages with mild signs and symptoms that may be difficult to notice. Some early warning signs of Parkinson’s disease may include¹⁰:

• Loss of smell
• Difficulty sleeping
• Small handwriting
• Shaking or tremors
• Constipation
• Speaking more softly than normal
• Difficulty walking
• Hunched posture while standing
• Serious or angry facial expressions, even when in a happy mood
• Muscle stiffness or pain
• Dizziness upon standing

Parkinson’s disease stages

The progression of Parkinson’s disease has been broken down into five stages¹¹. Because the disease can affect people differently, not all patients with Parkinson’s disease will experience the same severity or number of symptoms.

The first two stages of PD are considered mild, the third stage moderate, and the fourth and fifth stages severe.

• Stage 1: Stage 1 symptoms are mild and usually seen only on one side of the body, such as a tremor in one hand or a feeling of heaviness in one leg. At this stage, healthcare providers may be unable to make a definitive diagnosis and may instead opt to monitor the progression of your symptoms.
• Stage 2: The symptoms of stage 2 PD may begin to appear anywhere from a few months to multiple years after those of stage 1. Symptoms in this stage progress from affecting one side of the body (unilateral involvement) to affecting both sides (bilateral involvement). New indicators or behaviors may also develop, including loss of facial expressions, speech abnormalities, soft-spokenness and/or slurred speech, decreased blinking reflexes, stooped or hunched posture, and neck or back pain. Typically, a diagnosis of Parkinson’s disease can be made at this stage if your symptoms are accompanied by tremors.
• Stage 3: The key characteristic of stage 3 is the loss of balance and significantly slowed movement. In this moderately severe stage, it is common for patients to experience problems in adjusting their balance while walking or standing, which can lead to frequent falls. Generally, patients at this stage of Parkinson’s disease are still able to lead independent lives without needing assistance in completing daily activities.
• Stage 4: Stage 4 Parkinson’s disease is categorized as severe because it is marked by the progression of symptoms to the point that assistance is needed for daily activities, such as getting dressed, eating, and bathing.
• Stage 5: In the final stage of Parkinson’s disease, the patient may be unable to get out of bed without assistance and require continuous care to reduce the risk of potential falls. In some instances, people at this stage experience visual hallucinations (seeing things that aren’t there). It’s important to note that not everyone diagnosed with Parkinson’s disease will progress to stage 5.

Keep in mind that these stages are general guidelines for your provider to incorporate into your diagnosis. Some people with Parkinson’s disease don’t display every symptom listed.

However, it’s important to speak with a healthcare provider if you or a loved one begins to display the signs and symptoms of Parkinson’s disease, as early intervention can help increase the effectiveness of prescribed treatments.

Complications from Parkinson’s disease

Parkinson’s disease can affect the body and brain in different ways. Your healthcare provider may prescribe additional medications to treat these complications¹². As PD progresses, it has the potential to cause problems with the following:

• Cognition (thinking) difficulties: Cognitive decline and/or dementia can be seen in patients in the later stages of Parkinson’s disease. Typically, these symptoms are not as responsive to medications as are the other symptoms of PD.
• Depression and/or emotional changes: Some people with PD experience changes in their mood or develop signs of depression. Talk to your provider if you feel depressed, as there are many options to help you feel better, including psychotherapy (counseling) and/or medications.
• Problems with swallowing/chewing/eating: Late-stage PD can affect the muscles in the mouth and cause saliva to accumulate due to a slowed ability to swallow food. Difficulty chewing and swallowing can present issues with choking and not getting adequate nutrition through oral food intake alone.
• Problems sleeping and/or sleep disorders: Some people with PD can experience disrupted sleep patterns, such as the inability to sleep through the night or waking in the early hours, followed by tiredness during the day. In some cases, a healthcare provider may recommend medication to help make it easier to fall and stay asleep.
• Problems with urination and/or constipation: A few common complications of Parkinson’s disease are difficulty urinating, the inability to control urination (incontinence), and constipation due to slowed digestive tract function.
• Fatigue and/or pain: It is common for patients with PD to experience low energy levels and fatigue throughout the day.
• Changes in ability to smell: Though the cause is unknown, some people with PD experience changes in their senses of smell, such as the inability to differentiate between certain odors.
• Blood pressure changes: Orthostatic hypertension, or dizziness upon standing, is a common effect seen in people with PD.
• Sexual dysfunction: Decreased sexual desire or sexual performance has been noted as a complication of PD. This can be addressed and managed by your healthcare provider or a specialist.
• Cardiovascular disease: Having Parkinson’s disease puts a person at greater risk for developing heart diseases, such as heart attacks or strokes. Those with PD are twice as likely as those without it to develop heart disease and 50% more likely to die from it.
• Diabetes: Approximately 50–80% of people with Parkinson’s disease have abnormal glucose tolerance tests (tests used to measure how well the body uses glucose, or blood sugar). Abnormal glucose tolerance tests can indicate both prediabetes and diabetes. An estimated 8–30% of people who have Parkinson’s disease also have type 2 diabetes.