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Parkinson's disease
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Parkinson's Disease

Parkinson's disease is a progressive neurological disorder that impacts balance, movement, and cognitive function, typically marked by tremors, muscle rigidity, and slowness of movement.

Overview

Parkinson's disease is a progressive disorder of the nervous system. It affects several regions of the brain, particularly an area known as the substantia nigra, which is responsible for controlling balance and movement.

The condition is categorized according to the age at which symptoms begin:

  • Late-onset Parkinson's disease: Begins after age 50 and represents the most common form.
  • Early-onset Parkinson's disease: Signs and symptoms start before age 50.
  • Juvenile-onset Parkinson's disease: A subtype of early-onset disease that begins before age 20.

Symptoms

The earliest sign of Parkinson's disease is frequently a resting tremor—a trembling or shaking of a limb when the body is at rest. It typically starts on one side of the body, most often in one hand, but can eventually involve the arms, legs, feet, and face.

Characteristic motor symptoms include:

  • Tremor: Involuntary shaking occurring at rest.
  • Rigidity: Muscle stiffness affecting the limbs and torso.
  • Bradykinesia: Pathologically slow movement, which may progress to akinesia (an inability to move).
  • Postural Instability: Impaired coordination and balance.

Over time, these motor symptoms progressively worsen. Parkinson's disease also affects cognition and emotional health. Individuals may experience:

  • Depression
  • Visual hallucinations
  • Dementia: A progressive decline in memory, judgment, and other intellectual abilities.

Frequency

Parkinson's disease affects more than 1 million individuals in North America and more than 4 million people globally. In the United States, it occurs in approximately 13 out of every 100,000 individuals, with roughly 60,000 new cases diagnosed each year. Because the risk rises with advancing age and general life expectancy is increasing, the prevalence is projected to rise in the coming decades.

Causes & Genetics

Most cases of Parkinson's disease are classified as sporadic, occurring in individuals without a family history of the disorder. These sporadic cases likely arise from a complex interplay of genetic and environmental influences, though the exact causes remain unclear.

Approximately 15 percent of affected individuals have a family history of the condition. Familial forms can be caused by mutations in specific genes, including:

  • LRRK2
  • PARK7
  • PINK1
  • PRKN
  • SNCA

Variations in other genes, such as GBA1 and UCHL1, do not directly cause the condition but appear to modify the risk of developing it. Other genes associated with Parkinson's disease include ATP13A2 and VPS35.

Biological Mechanisms

Symptoms emerge primarily from the impairment or death of nerve cells (neurons) in the substantia nigra. These cells produce dopamine, a chemical messenger responsible for transmitting signals that generate smooth physical movements. When dopamine-producing cells die, communication between the brain and muscles deteriorates, resulting in loss of motor control.

Underlying mechanisms linked to genetic variations include:

  • Protein Clearance Defects: Disruptions in the cellular machinery that breaks down unwanted proteins, causing undegraded proteins to accumulate and damage neurons.
  • Mitochondrial Dysfunction: Abnormalities in cellular energy-producing structures (mitochondria). Mitochondria generate unstable molecules called free radicals as a byproduct; when protective mechanisms fail, free radicals accumulate and kill dopamine-producing cells.
  • Lewy Bodies: Abnormal protein deposits that appear inside dead or dying neurons in most cases. When Lewy bodies are absent, the condition is often referred to as parkinsonism.

Inheritance

The inheritance pattern depends on the underlying genetic cause:

  • Autosomal Dominant: When linked to the LRRK2 or SNCA genes, one copy of the altered gene in each cell is sufficient to cause the condition. Most affected people have one affected parent.
  • Autosomal Recessive: When associated with PARK7, PINK1, or PRKN, both copies of the gene must harbor mutations. Parents typically carry one copy of the mutated gene without showing symptoms.
  • Sporadic or Complex: In sporadic cases or cases involving risk-modifying genes, the inheritance pattern is generally unknown.

Other Names for This Condition

  • Parkinson disease
  • PD
  • Primary parkinsonism

Frequently Asked Questions

The wearing-off effect occurs when a dose of levodopa provides symptomatic relief for a shorter duration than before, causing motor and non-motor symptoms to return before the next scheduled dose. Clinicians address this by adjusting the dose frequency, utilizing extended-release carbidopa-levodopa formulations, or adding adjunctive medications like dopamine agonists, catechol-O-methyltransferase (COMT) inhibitors, or monoamine oxidase B (MAO-B) inhibitors.
Regular, high-intensity aerobic exercise (such as cycling, brisk treadmill walking, and boxing programs) has been shown to support neuroplasticity and improve gait, balance, and motor scores. Targeted physical therapy helps reduce fall risk, occupational therapy assists with adaptive strategies for daily activities, and specialized speech therapies (such as the Lee Silverman Voice Treatment, or LSVT LOUD) help combat hypophonia and swallowing dysfunction.
Evaluation for DBS is typically considered when a patient has had Parkinson's disease for at least four to five years, continues to experience a positive motor response to levodopa, but develops disabling medication-induced dyskinesias or severe motor fluctuations that can no longer be controlled by medication adjustments. Patients must be screened to ensure the absence of severe cognitive decline, active dementia, or untreated psychiatric illness.
Non-motor symptoms can appear years or even decades prior to the onset of resting tremors or motor stiffness. Common early signs include REM sleep behavior disorder (acting out vivid dreams during sleep), chronic constipation, progressive loss of the sense of smell (hyposmia or anosmia), orthostatic hypotension (blood pressure drops upon standing), and new or worsening mood disorders such as anxiety and depression.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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