Conditions

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Parkinson’s disease (PD), or simply Parkinson’s, is a neurodegenerative disease of mainly the central nervous system that affects both the motor and non-motor systems of the body. The symptoms usually emerge slowly, and, as the disease progresses, non-motor symptoms become more common. Usual symptoms include tremors, slowness of movement, rigidity, and difficulty with balance, collectively known as parkinsonism. Parkinson’s disease dementia, falls and neuropsychiatric problems such as sleep abnormalities, psychosis, mood swings, or behavioral changes may also arise in advanced stages.

Most cases of Parkinson’s disease are sporadic, but a few contributing factors have been identified. Pathophysiology is characterized by progressively expanding nerve cell death originating in substantia nigra, a midbrain region that supplies dopamine to the basal ganglia, a system involved in voluntary motor control. The cause of this cell death is poorly understood but involves alpha-synuclein aggregation into Lewy bodies within the neurons. Other possible factors involve genetic and environmental mechanisms, medications, lifestyle, and previous conditions.

Diagnosis is mainly based on signs and symptoms, usually motor-related, found via neurological examination, though medical imaging like neuromelanin MRI can support the diagnosis. Usual onset is in people over 60 years of age, of whom about one percent are affected. In those younger than 50, it is termed “early-onset PD”.

No cure is known; treatment aims to mitigate symptoms. Initial treatment typically includes L-DOPA, MAO-B inhibitors, or dopamine agonists. As the disease progresses, these medications become less effective and produce a side effect marked by involuntary muscle movements. Diet and certain forms of rehabilitation have shown some effectiveness at improving symptoms. Deep brain stimulation has been used to reduce severe motor symptoms when drugs are ineffective. There is little evidence for treatment of the non-movement-related symptoms, such as sleep disturbances and mood instability. The average life expectancy is near-normal.

Classification and terminology
See also: Parkinsonism and Parkinson-plus syndrome
Parkinson’s disease (PD) is a neurodegenerative disease affecting both the central and peripheral nervous systems, characterized by the loss of dopamine-producing neurons in the substantia nigra region of the brain.[7] It is classified as a synucleinopathy due to the abnormal accumulation of the protein alpha-synuclein, which aggregates into Lewy bodies within affected neurons.[8]

The loss of dopamine-producing neurons in the substantia nigra initially presents as movement abnormalities, leading to Parkinson’s further categorization as a movement disorder.[9] In 30% of cases, disease progression leads to the cognitive decline known as Parkinson’s disease dementia (PDD).[10] Alongside dementia with Lewy bodies, PDD is one of the two subtypes of Lewy body dementia.[11]