Parkinson’s disease (PD), or simply Parkinson’s, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms become more common. The most obvious early symptoms are tremor, rigidity, slowness of movement, and difficulty with walking. Cognitive and behavioral problems may also occur with depression, anxiety, and apathy occurring in many people with PD. Parkinson’s disease dementia becomes common in the advanced stages of the disease. Those with Parkinson’s can also have problems with their sleep and sensory systems. The motor symptoms of the disease result from the death of cells in the substantia nigra, a region of the midbrain, leading to a dopamine deficit. The cause of this cell death is poorly understood, but involves the build-up of misfolded proteins into Lewy bodies in the neurons. Collectively, the main motor symptoms are also known as parkinsonism or a parkinsonian syndrome.
The cause of PD is unknown, with both inherited and environmental factors being believed to play a role. Those with a family member affected by PD are at an increased risk of getting the disease, with certain genes known to be inheritable risk factors. Other risk factors are those who have been exposed to certain pesticides and who have prior head injuries. Coffee drinkers, tea drinkers, and tobacco smokers are at a reduced risk.
Diagnosis of typical cases is mainly based on symptoms, with motor symptoms being the chief complaint. Tests such as neuroimaging (magnetic resonance imaging or imaging to look at dopamine neuronal dysfunction known as DaT scan) can be used to help rule out other diseases. Parkinson’s disease typically occurs in people over the age of 60, of whom about one percent are affected. Males are more often affected than females at a ratio of around 3:2. When it is seen in people before the age of 50, it is called early-onset PD. By 2015, PD affected 6.2 million people and resulted in about 117,400 deaths globally. The average life expectancy following diagnosis is between 7 and 15 years.
No cure for PD is known; treatment aims to reduce the effects of the symptoms. Initial treatment is typically with the medications levodopa (L-DOPA), MAO-B inhibitors, or dopamine agonists. As the disease progresses, these medications become less effective, while at the same time producing a side effect marked by involuntary muscle movements. At that time, medications may be used in combination and doses may be increased. Diet and certain forms of rehabilitation have shown some effectiveness at improving symptoms. Surgery to place microelectrodes for deep brain stimulation has been used to reduce motor symptoms in severe cases where drugs are ineffective. Evidence for treatments for the nonmovement-related symptoms of PD, such as sleep disturbances and emotional problems, is less strong.
The disease is named after English doctor James Parkinson, who published the first detailed description in An Essay on the Shaking Palsy, in 1817. Public awareness campaigns include World Parkinson’s Day (on the birthday of James Parkinson, 11 April) and the use of a red tulip as the symbol of the disease. People with PD who have increased the public’s awareness of the condition include boxer Muhammad Ali, actor Michael J. Fox, Olympic cyclist Davis Phinney, and actor Alan Alda.