Parkinson's Disease Glossary

Parkinson's disease comes with its own vocabulary. From clinical terms your neurologist uses to research concepts you encounter in the news, understanding the language can help you feel more confident in conversations with your healthcare team and more informed when reading about your condition.

This glossary defines 61 terms related to Parkinson's disease diagnosis, symptoms, medications, therapies, and research. Each definition is written in plain English and sourced from published medical literature. Use the letter navigation or search to find specific terms.

A

Alpha-Synuclein: A protein that accumulates abnormally in the brains of people with Parkinson's disease, forming clumps called Lewy bodies. Research into alpha-synuclein is a major focus of PD drug development.
Akinesia: Loss or impairment of the ability to initiate voluntary movement. A more severe form of bradykinesia, often used to describe complete inability to move.
Apomorphine: A potent dopamine agonist used as a rescue injection (Apokyn) or sublingual film (Kynmobi) for acute off-episodes in Parkinson's disease. Despite the name, it is not related to morphine. Provides the fastest relief of any PD medication (10-20 minutes).
Atypical Parkinsonism: A group of neurodegenerative disorders that share some features with Parkinson's disease but have distinct characteristics and generally poorer prognosis. Includes progressive supranuclear palsy (PSP), multiple system atrophy (MSA), corticobasal degeneration (CBD), and dementia with Lewy bodies (DLB).
Axial Symptoms: Motor symptoms affecting the trunk and midline of the body, including postural instability, gait disturbance, speech and swallowing difficulties, and freezing of gait. Axial symptoms respond less well to levodopa than limb symptoms and are a major source of disability in advanced PD.

B

Basal Ganglia: A group of structures deep within the brain that help regulate movement. In Parkinson's disease, loss of dopamine in the basal ganglia leads to motor symptoms.
Bradykinesia: Slowness of movement, one of the cardinal features of Parkinson's disease. Manifests as difficulty initiating movements, reduced arm swing, smaller handwriting, and softer speech.
Biomarker: A measurable indicator of a biological state or condition. In PD research, biomarkers may include alpha-synuclein levels in cerebrospinal fluid, DaTscan imaging, skin biopsy for alpha-synuclein, and blood-based tests. Reliable biomarkers are crucial for early diagnosis and tracking disease progression.
Bradyphrenia: Slowness of thought or cognitive processing speed, the mental equivalent of bradykinesia. Patients may take longer to respond to questions, process information, or make decisions. Often an early cognitive sign of PD that precedes frank dementia.

C

Carbidopa: A medication that prevents levodopa from being converted to dopamine outside the brain. Always given with levodopa (as Sinemet) to reduce nausea and increase the amount of levodopa reaching the brain.
COMT Inhibitor: A class of medications (entacapone, opicapone, tolcapone) that block the COMT enzyme, which breaks down levodopa and dopamine. Extends the effectiveness of each levodopa dose.
Caregiver Burden: The physical, emotional, social, and financial toll experienced by people who provide ongoing care for someone with Parkinson's disease. As PD progresses, caregiver burden increases. Includes fatigue, depression, social isolation, and financial strain. Respite care and support groups are essential resources.
Cortical: Relating to the cerebral cortex, the outer layer of the brain responsible for higher functions including thinking, planning, language, and consciousness. In PD, cortical involvement in later stages contributes to cognitive decline and dementia.
Camptocormia: An abnormal involuntary forward flexion of the trunk that appears when standing or walking and resolves when lying down. Also called 'bent spine syndrome.' Caused by dystonia of paraspinal muscles or myopathy. Can significantly impair mobility and quality of life.
Cogwheel Rigidity: A type of rigidity characterized by a ratchety, jerky resistance to passive movement, like turning a cogwheel. It results from tremor superimposed on lead-pipe rigidity. Cogwheel rigidity is a hallmark finding on neurological examination in Parkinson's disease.

D

Deep Brain Stimulation (DBS): A surgical treatment where electrodes are implanted in specific brain areas (usually the subthalamic nucleus or globus pallidus) and connected to a pulse generator. Used for advanced PD when medications cause troublesome fluctuations.
Dopamine: A neurotransmitter that plays a crucial role in controlling movement, motivation, and reward. In Parkinson's disease, dopamine-producing neurons in the substantia nigra progressively die, leading to motor symptoms.
Dopamine Agonist: A class of medications that directly stimulate dopamine receptors, mimicking the action of dopamine. Examples include pramipexole (Mirapex), ropinirole (Requip), and rotigotine (Neupro patch).
Dyskinesia: Involuntary, uncontrolled movements (writhing, twisting, or fidgeting) that often develop as a side effect of long-term levodopa use. Distinguished from tremor by its flowing, dance-like quality.
Dystonia: Sustained or repetitive muscle contractions causing abnormal postures or twisting movements. In PD, often affects the feet (especially in the morning) or neck. Can occur as a symptom or medication side effect.
Dementia: A syndrome of progressive cognitive decline severe enough to interfere with daily functioning. In PD, dementia (PDD) may develop in up to 80% of long-term survivors. Characterized by impaired executive function, attention, and visuospatial abilities. Rivastigmine is the only FDA-approved treatment for PDD.
Dopamine Transporter (DAT): A protein on dopamine neurons that recycles dopamine from the synapse back into the neuron. DAT levels are measured by DaTscan imaging to support PD diagnosis. Reduced DAT binding indicates loss of dopamine neurons.
Duopa (Carbidopa-Levodopa Enteral Suspension): A gel formulation of carbidopa/levodopa delivered continuously through a tube directly into the jejunum (small intestine) via a portable pump. Used for advanced PD with severe motor fluctuations when oral medications provide inadequate control.
Dysarthria: A motor speech disorder caused by weakness, slowness, or incoordination of the muscles used for speaking. In PD, dysarthria manifests as soft, monotone, breathy, or slurred speech. LSVT LOUD therapy is the gold standard treatment.
Dopaminergic: Relating to or affecting the neurotransmitter dopamine. Dopaminergic neurons produce dopamine, dopaminergic pathways transmit dopamine signals, and dopaminergic medications work by increasing dopamine activity in the brain. The nigrostriatal dopaminergic pathway is the one primarily affected in PD.
Drug Holiday: A planned, medically supervised temporary withdrawal from PD medications, historically used to try to restore drug sensitivity and reduce dyskinesia. Now largely abandoned due to risk of neuroleptic malignant-like syndrome, deep venous thrombosis, and significant patient suffering during the drug-free period.
Dual Tasking: The ability to perform two tasks simultaneously, such as walking while talking. Dual-task performance is significantly impaired in PD because movement no longer occurs automatically and requires conscious attention. Dual-task interference increases fall risk and is used as a clinical assessment tool.
Dyskinesia-Dystonia Spectrum: The range of involuntary movements in PD, from peak-dose dyskinesia (choreiform movements at highest levodopa levels) to diphasic dyskinesia (occurring as drug levels rise and fall) to off-period dystonia (sustained muscle contractions when medication wears off). Understanding where a patient falls on this spectrum guides treatment adjustments.

E

Enteric Nervous System: The extensive network of neurons lining the gastrointestinal tract, sometimes called the 'second brain.' Rich in dopamine neurons, it is affected early in PD by alpha-synuclein pathology. This may explain why constipation and GI symptoms often precede motor symptoms by years.
Executive Function: Higher-order cognitive abilities including planning, organizing, multitasking, problem-solving, and mental flexibility. Executive dysfunction is one of the earliest cognitive changes in PD, often present before memory problems become apparent.
End-of-Dose Wearing Off: The predictable reemergence of PD symptoms before the next scheduled medication dose, occurring as levodopa levels decline. The most common motor complication, typically appearing 3-5 years after starting levodopa. Both motor symptoms (tremor, rigidity) and non-motor symptoms (anxiety, pain) can wear off.

F

Festination: An involuntary tendency to take short, accelerating steps when walking, as if being pulled forward. A characteristic gait disturbance in Parkinson's disease that increases fall risk.
Freezing of Gait (FOG): A brief, episodic inability to produce effective stepping, often described as feeling that the feet are glued to the floor. Common during turns, in doorways, and when initiating walking.

G

Gait: The pattern and manner of walking. PD characteristically affects gait, causing short shuffling steps, reduced arm swing, difficulty initiating walking, festination (progressively faster small steps), and freezing of gait. Gait analysis is an important part of PD assessment.
GLP-1 Receptor Agonist: A class of medications originally developed for type 2 diabetes (e.g., exenatide, liraglutide, semaglutide) being investigated as potential neuroprotective treatments for PD. Early clinical trials show promising results in slowing motor symptom progression.

H

Hoehn and Yahr Scale: A clinical rating scale (stages 1-5) used to describe the progression of Parkinson's disease. Stage 1 is mildest (one-sided symptoms), Stage 5 is most severe (wheelchair-bound or bedridden).
Hypomimia: Reduced facial expression, often called 'masked face,' caused by bradykinesia and rigidity of facial muscles. One of the early signs of Parkinson's disease.

I

Impulse Control Disorder (ICD): A group of behavioral addictions that can develop as a side effect of dopamine agonists and, less commonly, levodopa. Includes pathological gambling, compulsive shopping, binge eating, and hypersexuality. Affects up to 17% of PD patients on dopamine agonists.

L

Levodopa (L-DOPA): The most effective medication for Parkinson's disease. A precursor to dopamine that can cross the blood-brain barrier. Always combined with carbidopa or benserazide to prevent peripheral conversion.
Lewy Bodies: Abnormal aggregates of protein (primarily alpha-synuclein) that develop inside nerve cells. They are the pathological hallmark of Parkinson's disease and Lewy body dementia.
Lewy Body Dementia (DLB): A progressive dementia characterized by Lewy body deposits throughout the cortex. Features include visual hallucinations, fluctuating cognition, parkinsonism, and REM sleep behavior disorder. Related to PDD — the distinction is based on timing of cognitive vs. motor symptoms (the 'one-year rule').

M

MAO-B Inhibitor: A class of medications that block the enzyme monoamine oxidase type B, which breaks down dopamine in the brain. Includes rasagiline (Azilect), selegiline (Eldepryl), and safinamide (Xadago).
Micrographia: Abnormally small handwriting that tends to get progressively smaller. A characteristic early sign of Parkinson's disease caused by bradykinesia and fine motor impairment.
Motor Fluctuations: Variations between periods of good symptom control ('on' time) and poor control ('off' time) that develop with long-term levodopa use. Include wearing-off, on-off phenomena, and dose failure.
MDS-UPDRS: The Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale. The gold-standard clinical assessment tool for PD, with four parts: I (non-motor experiences of daily living), II (motor experiences of daily living), III (motor examination), and IV (motor complications). Used in clinical trials and routine care.

N

Neurodegeneration: The progressive loss of structure and function of neurons. In Parkinson's disease, neurodegeneration primarily affects dopamine-producing neurons in the substantia nigra.
Neuroplasticity: The brain's ability to reorganize itself by forming new neural connections. Exercise-induced neuroplasticity is a key rationale for intensive exercise programs in PD, as vigorous exercise has been shown to promote dopamine release, increase brain-derived neurotrophic factor (BDNF), and potentially slow symptom progression.
Nocturia: The need to wake up during the night to urinate, one of the most common and disruptive autonomic symptoms in PD. Affects up to 60% of patients. Caused by detrusor overactivity from autonomic dysfunction, compounded by reduced bladder capacity, medications, and nighttime fluid intake.

O

On-Off Phenomenon: Unpredictable fluctuations between periods of good mobility ('on') and immobility ('off') in advanced Parkinson's disease. Unlike wearing off, these changes can occur suddenly and without relation to medication timing.
Off Time: Periods when PD medications are not providing adequate symptom control, resulting in return of motor symptoms (tremor, rigidity, bradykinesia) and non-motor symptoms (anxiety, pain, fatigue). Reducing off-time is a primary goal of treatment optimization in mid-to-advanced PD.
On-Off Fluctuations: Alternating periods of good medication response (on) and poor response (off) that develop with long-term levodopa use. Predictable wearing-off is the most common pattern; unpredictable on-off switching is more challenging to manage. Both motor and non-motor symptoms fluctuate.
Orthostatic Hypotension: A sustained drop in blood pressure of at least 20 mmHg systolic or 10 mmHg diastolic within 3 minutes of standing. In PD, caused by autonomic nervous system degeneration affecting cardiovascular reflexes. Increases fall risk and can cause dizziness, lightheadedness, visual dimming, and syncope.

P

Parkinsonism: A general term for any condition that causes the movement abnormalities seen in Parkinson's disease (tremor, bradykinesia, rigidity). Includes PD and other conditions like PSP, MSA, and drug-induced parkinsonism.
Postural Instability: Impaired balance and righting reflexes, assessed clinically with the pull test. One of the cardinal features of PD, typically appearing in Stage 3 or later. The least responsive to levodopa of the cardinal symptoms. Major contributor to falls, the leading cause of injury-related hospitalization in PD.
Proprioception: The sense of body position and movement in space, relayed by receptors in muscles, tendons, and joints. Proprioception is impaired in PD, contributing to postural instability and gait difficulty. Physical therapy targeting proprioceptive awareness can improve balance outcomes.

R

REM Sleep Behavior Disorder (RBD): A sleep disorder in which patients physically act out vivid dreams during REM sleep due to loss of normal muscle atonia. A strong prodromal marker for PD — over 80% of people with RBD eventually develop PD or a related synucleinopathy within 10-15 years. Can cause injury to patient or bed partner.

S

Substantia Nigra: A region in the midbrain that produces dopamine. In Parkinson's disease, neurons in the substantia nigra pars compacta progressively die, leading to dopamine deficiency and motor symptoms.
Sialorrhea: Excessive drooling or saliva pooling in the mouth. In PD, caused not by excess saliva production but by reduced frequency of automatic swallowing. Treatments include glycopyrrolate, atropine sublingual drops, and botulinum toxin injections into the salivary glands.
Striatum: A region of the basal ganglia comprising the caudate nucleus and putamen. The striatum receives dopaminergic input from the substantia nigra and plays a critical role in motor planning and execution. Dopamine depletion in the striatum is the direct cause of motor symptoms in PD.

U

UPDRS (Unified Parkinson's Disease Rating Scale): The original standardized clinical rating scale for PD, now largely replaced by the MDS-UPDRS. Measures motor and non-motor symptoms, activities of daily living, and treatment complications. Scores range from 0 (no disability) to 199 (total disability).

W

Wearing Off: A predictable return of PD symptoms before the next medication dose is due, indicating that the benefit of each levodopa dose is not lasting long enough. The most common type of motor fluctuation.