Parkinson's disease

Parkinson's disease (PD) is a progressive neurological disorder and the most common form of parkinsonism, a broader group of conditions that affect movement. The four commonly described motor features are bradykinesia (slowness of movement), rigidity, tremor—often most noticeable at rest—and impaired balance or posture. Their combination and severity differ from person to person; not everyone with PD develops a tremor, and similar symptoms can arise from other disorders. PD can also affect sleep, mood, thinking, digestion, pain and other bodily functions. Symptoms often begin gradually and may be more noticeable on one side at first, but the course is variable.

Many movement symptoms are linked to the impairment and loss of dopamine-producing neurons in the substantia nigra, a brain region involved in movement control. Dopamine helps circuits involved in smooth, purposeful movement communicate. In many people with PD, brain cells also contain Lewy bodies—clumps involving the protein alpha-synuclein—but scientists continue to investigate how these changes relate to the disease. In most cases the precise cause is unknown. Inherited genetic variants account for some cases, while research also links risk to environmental exposures; age is an important risk factor. These findings do not mean that a single exposure or gene explains most cases.

The English physician James Parkinson published An Essay on the Shaking Palsy in 1817, bringing together clinical observations of a syndrome later named for him. Modern diagnosis is primarily clinical: health professionals consider a person's history, symptoms and neurological examination, while tests may be used to investigate other causes or support assessment. There is no single test that definitively identifies every case, and several other neurological disorders can produce Parkinson-like features. Distinguishing PD from these conditions matters because their course and response to treatment may differ.

There is no cure that stops or reverses Parkinson's disease, but treatment can reduce symptoms and support daily function. Levodopa, usually combined with carbidopa, is a common medicine that helps replenish dopamine in the brain and often improves movement symptoms; its effects and possible side effects vary. Other medicines may address particular motor or non-motor symptoms. For some people, deep-brain stimulation can help selected movement problems, while physical, occupational and speech therapy and rehabilitation can support mobility, communication and everyday activities. Treatment is individualized and may change as the condition progresses. Access to diagnosis, medicines and ongoing care is uneven around the world, a concern highlighted by the World Health Organization.