Parkinson’s disease is caused by the dysfunction and death of dopamine-producing neurons (nerve cells) in the brain. Parkinsonism is a broader term that encompasses Parkinson’s disease itself, as well as other conditions that cause motor symptoms similar to those seen in Parkinson’s, like tremor and abnormally slow movement.
Most people diagnosed with Parkinson’s disease (about 80%–85%) have primary parkinsonism, better known simply as Parkinson’s disease. This type is also sometimes called idiopathic Parkinson’s, meaning that the specific cause of the disease is unknown. This type tends to respond well to medicines, such as levodopa and its derivates, that work by increasing or substituting dopamine molecules in the brain.
Mutations in certain genes are known to increase a person’s risk of Parkinson’s, or cause the disease outright. Because these mutated genes can be passed from parents to their biological children, the disease can run in families — sometimes referred to as familial Parkinson’s disease. About 15% of people diagnosed with Parkinson’s have a family history of the disease.
Exactly how this type of Parkinson’s manifests, and how it is inherited, depends on the specific genetic mutation. For example, mutations in the gene SCNA are generally associated with early-onset disease, whereas LRRK2 mutations are associated with later-onset disease.
Parkinson’s disease is most often diagnosed in people in their 60s, but it can also affect people at younger ages. Around 10%–20% of people with Parkinson’s are diagnosed before age 50, and are said to have early-onset or young-onset Parkinson’s. Among these patients, roughly half are diagnosed before they’re 40.
Because Parkinson’s is more common in older individuals, younger patients may experience more difficulty getting the correct diagnosis.
Compared to those that develop the disease later in life, people with early-onset Parkinson’s more often have a family history of the disease, and they tend to experience slower disease progression. People with early-onset disease are more likely to experience involuntary movement problems as a side effect to medications like levodopa, but they are less likely to experience memory loss, confusion, and balance problems.
While symptoms of Parkinson’s are generally similar no matter what age it appears, the disease tends to affect younger people differently. Because younger patients are at a different stage in life, the disease causes unique psychological and social challenges, such as having to coordinate medical care alongside adult responsibilities like jobs and children.
The remaining types of Parkinson’s are termed secondary or atypical parkinsonism, sometimes called Parkinson’s Plus. These conditions cause motor symptoms that are similar to those that develop in Parkinson’s disease, but the underlying biological cause is different.
While it can be very difficult to differentiate Parkinson’s disease and secondary parkinsonism, a key difference is that dopaminergic medications such as levodopa are generally effective in people with primary disease, but not in those with secondary parkinsonism.
Secondary parkinsonism includes dementia with Lewy bodies, corticobasal degeneration, progressive supranuclear palsy, and multiple system atrophy.
Dementia with Lewy bodies
Dementia with Lewy bodies, or Lewy Body Dementia, is a particular form of dementia associated with Parkinson’s disease. It is caused by Lewy bodies (clumps of alpha-synuclein protein) forming in the brain. The condition tends to occur early in the progression of the disease and leads to a progressive deterioration of cognitive functions such as thinking, memory, and judgment.
Progressive supranuclear palsy
Progressive supranuclear palsy (PSP) is one of the more common forms of secondary parkinsonism. As with idiopathic Parkinson’s disease, progressive supranuclear palsy usually appears later in life, but the symptoms tend to progress far more rapidly once they appear. Compared to those with Parkinson’s disease, people with PSP are more likely to have eye movement abnormalities and speech problems, but less likely to experience tremor.
PSP is caused by the buildup of a protein called tau in brain cells, which causes the cells to function improperly and eventually die. The abnormal buildup of tau also occurs in other neurological diseases, like Alzheimer’s.
Like PSP, corticobasal degeneration is caused by a buildup of tau protein, which damages parts of the brain. The condition tends to appear with motor symptoms that start on one side of the body and slowly spread to other areas over time. Other symptoms, like cognitive and speech problems, may also occur. This is the least common of the atypical parkinsonisms.
Multiple system atrophy
Multiple system atrophy (MSA) is characterized by motor symptoms and by symptoms that affect the autonomic nervous system — the part of the nervous system that regulates unconscious processes like breathing, blood pressure, and digestion. Although the cause of MSA is not clear, it is often characterized by a buildup of the protein alpha-synuclein in certain brain cells. In MSA, symptoms tend to progress more rapidly than in Parkinson’s disease.
Several conditions associated with Parkinson’s disease include drug-induced parkinsonism, vascular parkinsonism or normal pressure hydrocephalus.
Certain medications, most notably some antipsychotics, can cause a person to develop Parkinson’s-like symptoms as a side effect. Next to primary Parkinson’s disease, this is the most common type of parkinsonism. Drug-induced parkinsonism may be difficult to distinguish from Parkinson’s disease, but symptoms will generally improve in the weeks or months after use of the medication has stopped.
Also called cerebrovascular disease or multi-infarct parkinsonism, this type of parkinsonism is caused by a series of small strokes that kill cells in certain parts of the brain, leading to symptoms similar to those of Parkinson’s.
This type of Parkinson’s is characterized by symptoms in the lower half of the body (such as walking difficulties and urinary incontinence) and memory loss, whereas tremor is less common. Vascular parkinsonism becomes more common with age, especially in people with diabetes.
Normal pressure hydrocephalus
This condition is caused by the cerebrospinal fluid or CSF (the fluid that surrounds the brain and spinal cord) accumulating in cavities in the brain. This essentially results in swelling in the brain, which can disrupt or damage brain tissue.
The symptoms of NSA are very similar to those seen in vascular parkinsonism, and may be confused with other neurological conditions like Alzheimer’s disease. NSA is typically treated by removing excess CSF through a procedure like a lumbar puncture (also called a spinal tap), where CSF is removed via a needle inserted into the spine.
Infections, toxins, and trauma
Some infectious conditions, such as encephalitis and AIDS, can cause symptoms similar to Parkinson’s disease. Such symptoms may also be caused by exposure to toxins like carbon monoxide or by brain trauma, tumors, hypoxia (a lack of oxygen) in the brain, and some metabolic disorders like hypocalcemia (abnormally low calcium levels).
Last updated: Aug. 30, 2021
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