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Protected Parkinson's disease (also known as PD or Parkinson disease) is a degenerative disorder of the central nervous system, that affects the control of muscles, and so may affect movement, speech and posture. Parkinson's disease belongs to a group of conditions called movement disorders. It is often characterized by muscle rigidity, tremor, a slowing of physical movement (bradykinesia), and in extreme cases, a loss of physical movement (akinesia). The primary symptoms are due to excessive muscle contraction, normally caused by the insufficient formation and action of dopamine, which is produced in the dopaminergic neurons of the brain. PD is both chronic, meaning it persists over a long period of time, and progressive.

PD is the most common cause of parkinsonism, a group of similar symptoms. PD is also called "primary parkinsonism" or "idiopathic PD" ("idiopathic" meaning of no known cause). While most forms of parkinsonism are idiopathic, there are some cases where the symptoms may result from toxicity, drugs, genetic mutation, head trauma, or other medical disorders.

History

Symptoms of Parkinson's disease have been known and treated since ancient times. However, it was not formally recognised and its symptoms documented until 1817 in An Essay on the Shaking Palsy by the British physician Dr. James Parkinson. Parkinson's disease was then known as paralysis agitans. The underlying biochemical changes in the brain were identified in the 1950s, due largely to the work of Swedish scientist Arvid Carlsson who later went on to win a Nobel prize. L-dopa entered clinical practice in 1967*, and the first study reporting improvements in patients with Parkinson's disease resulting from treatment with L-dopa was published in 1968.

Symptoms

Parkinson disease affects movement (motor symptoms). Typical other symptoms include disorders of mood, behavior, thinking, and sensation (non-motor symptoms). Individual patients' symptoms may be quite dissimilar; progression is also distinctly individual.

There are four major dopamine pathways in the brain; the nigrostriatal pathway, referred to above, mediates movement and is the most conspicuously affected in early Parkinson's disease. The other pathways are the mesocortical, the mesolimbic, and the tuberoinfundibular. These pathways are associated with, respectively: volition and emotional responsiveness; desire, initiative, and reward; and sensory processes and maternal behavior. Reduction in dopamine along the non-striatal pathways is the likely explanation for much of the neuropsychiatric pathology associated with Parkinson's disease.

Motor symptoms

The cardinal symptoms are:
  • tremor: normally 4-7Hz tremor, maximal when the limb is at rest, and decreased with voluntary movement. It is typically unilateral at onset. This is the most apparent and well-known symptom. However, an estimated 30% of patients have little perceptible tremor; these are classified as akinetic-rigid.
  • rigidity: stiffness; increased muscle tone. In combination with a resting tremor, this produces a ratchety, "cogwheel" rigidity when the limb is passively moved.
  • bradykinesia/akinesia: respectively, slowness or absence of movement. Rapid, repetitive movements produce a dysrhythmic and decremental loss of amplitude.
  • postural instability: failure of postural reflexes, which leads to impaired balance and falls.

Other motor symptoms include:

  • Gait and posture disturbances:
    • Shuffling: gait is characterized by short steps, with feet barely leaving the ground, producing an audible shuffling noise. Small obstacles tend to trip the patient
    • Decreased arm swing: a form of bradykinesia
    • Turning "en bloc": rather than the usual twisting of the neck and trunk and pivoting on the toes, PD patients keep their neck and trunk rigid, requiring multiple small steps to accomplish a turn.
    • Stooped, forward-flexed posture. In severe forms, the head and upper shoulders may be bent at a right angle relative to the trunk (camptocormia).
    • Festination: a combination of stooped posture, imbalance, and short steps. It leads to a gait that gets progressively faster and faster, often ending in a fall.
    • Gait freezing: "freezing" is another word for akinesia, the inability to move. Gait freezing is characterized by inability to move the feet, especially in tight, cluttered spaces or when initiating gait.
    • Dystonia: abnormal, sustained, painful twisting muscle contractions, usually affecting the foot and ankle in PD patients. This causes toe flexion and foot inversion, interfering with gait.
  • Speech and swallowing disturbances
    • Hypophonia: soft speech. Speech quality tends to be soft, hoarse, and monotonous.
    • Festinating speech: excessively rapid, soft, poorly-intelligible speech.
    • Drooling: most likely caused by a weak, infrequent swallow and stooped posture.
    • (Non-motor causes of speech/language disturbance in both expressive and receptive language: these include decreased verbal fluency and cognitive disturbance especially related to comprehension of emotional content of speech and of facial expression
    • Dysphagia: impaired ability to swallow. Can lead to aspiration, pneumonia, and ultimately death.
  • Other motor symptoms:
    • fatigue (up to 50% of cases);
    • masked facies (a mask-like face also known as hypomimia), with infrequent blinking;
    • difficulty rolling in bed or rising from a seated position;
    • micrographia (small, cramped handwriting);
    • impaired fine motor dexterity and coordination;
    • impaired gross motor coordination;
    • Poverty of movement: overall loss of accessory movements, such as decreased arm swing when walking, as well as spontaneous movement.

Non-motor symptoms

Mood disturbances
  • Estimated prevalance rates of depression vary widely according to the population sampled and methodology used. Reviews of depression estimate its occurrence in anywhere from 20-80% of cases. Estimates from community samples tend to find lower rates than from specialist centres. Most studies use self-report questionnaires such as the Beck Depression Inventory which may overinflate scores due to physical symptoms. Studies using diagnostic interviews by trained psychiatrists also report lower rates of depression.

  • More generally, there is an increased risk for any individual with depression to go on to develop Parkinson's disease at a later date.
  • Seventy percent of individuals with Parkinson's disease diagnosed with pre-existing depression go on to develop anxiety. Ninety percent of Parkinson's disease patients with pre-existing anxiety subsequently develop depression); apathy or abulia.

Cognitive disturbances
  • slowed reaction time; both voluntary and involuntary motor responses are significantly slowed.
  • executive dysfunction, characterized by difficulties in: differential allocation of attention, impulse control, set shifting, prioritizing, evaluating the salience of ambient data, interpreting social cues, and subjective time awareness. This complex is present to some degree in most Parkinson's patients; it may progress to:
  • dementia: a later development in approximately 20-40% of all patients, typically starting with slowing of thought and progressing to difficulties with abstract thought, memory, and behavioral regulation.
  • memory loss; procedural memory is more impaired than declarative memory. Prompting elicits improved recall.
  • medication effects: some of the above cognitive disturbances are improved by dopaminergic medications, while others are actually worsened

Sleep disturbances
  • Excessive daytime somnolence;
  • Initial, intermediate, and terminal insomnia;
  • Disturbances in REM sleep: disturbingly vivid dreams, and REM Sleep Disorder, characterized by acting out of dream content;
Sensation disturbances
  • impaired visual contrast sensitivity, spatial reasoning, colour discrimination, convergence insufficiency (characterized by double vision) and oculomotor control
  • dizziness and fainting; usually attributable orthostatic hypotension, a failure of the autonomous nervous system to adjust blood pressure in response to changes in body position
  • impaired proprioception (the awareness of bodily position in three-dimensional space)
  • loss of sense of smell (anosmia),
  • pain: neuropathic, muscle, joints, and tendons, attributable to tension, dystonia, rigidity, joint stiffness, and injuries associated with attempts at accommodation

Autonomic disturbances

Diagnosis

There are currently no blood or laboratory tests that have been proven to help in diagnosing sporadic PD. Therefore the diagnosis is based on medical history and a neurological examination. The disease can be difficult to diagnose accurately. Early signs and symptoms of PD may sometimes be dismissed as the effects of normal aging. The physician may need to observe the person for some time until it is apparent that the symptoms are consistently present. Doctors may sometimes request brain scans or laboratory tests in order to rule out other diseases. However, CT and MRI brain scans of people with PD usually appear normal.

Descriptive epidemiology

The worldwide prevalence of Parkinson's disease is 4 to 6 million people. There are over 1.5 million in China alone. The disease usually has a long, subtle onset, so diagnosis occurs most often after many years of subclinical disease . Prevalence estimates range from a low of 7 per 100,000 in Ethiopia to a high of 329.3 per 100,000 in Nebraska, U.S.A. (although that figure was arrived at using capture-recapture estimates), and 328.3 cases per 100,000 in the Parsi community in Bombay, India. The greatest prevalence of any country is the U.S.A., with between 100 and 250 cases per 100,000.

The average age at which symptoms begin is 55-60, and although cases at ages as low as 11 have been reported it is highly unusual for people under 30 to develop Parkinson's. It occurs in all parts of the world, but appears to be more common in people of European ancestry than in those of African ancestry. Those of East Asian ancestry have an intermediate risk. It is more common in rural than urban areas in developed countries, but the converse is true in poorer countries, leading Tanner to speculate about environmental causes . Men are affected at a rate about double that of women, especially in the older age groups. There is a suggestion of increased prevalence in the California Hispanic population. About 2% of the population develops the disease some time during life .

Incidence has been estimated by several groups, starting with northern California. They observed age and sex corrected incidence of 13.4 per 100,000/year. They note a rapid increase in incidence with age, male rates nearly double female rates, and an elevated rate amongst Hispanics. This study was followed by a group in Spain who used the two-stage survey technique pioneered in the Copiah County study to survey a cohort age 65 to 85. Within that group, incidence adjusted for age and sex was 186.8/100,000 per year, with men's rates being 2.55 times that of women. For the same age group, Van den Eeden and colleagues observed an incidence of roughly 120/100,000/year. Soon thereafter the Rotterdam sudy was published using techniques similar to the Spanish group and Copiah County. They note age-specific incidence rates from 0.3 per 1000 person-years in subjects aged 55 to 65 years, to 4.4 per 1000 person-years for those aged ≥85 year, and a sex ratio of 1.55 for male incidence.

Related diseases

There are other disorders that are called Parkinson-plus diseases. These include:

Some people include dementia with Lewy bodies (DLB) as one of the 'Parkinson-plus' syndromes. Although idiopathic Parkinson's disease patients also have Lewy bodies in their brain tissue, the distibution is denser and more widespread in DLB. Even so, the relationship between Parkinson disease, Parkinson disease with dementia (PDD) and dementia with Lewy bodies (DLB) might be most accurately conceptualized as an spectrum, with a discrete area of overlap between each of the three disorders. The natural history and role of Lewy bodies is very little understood.

Patients often begin with typical Parkinson's disease symptoms which persist for some years; these Parkinson-plus diseases can only be diagnosed when other symptoms become apparent with the passage of time. These Parkinson-plus diseases usually progress more quickly than typical ideopathic Parkinson disease. The usual anti-Parkinson's medications are typically either less effective or not effective at all in controlling symptoms; patients may be exquisitely sensitive to neuroleptic medications like haloperidol. Additionally, the cholinesterase inhibiting medications have shown preliminary efficacy in treating the cognitive, psychiatric, and behavioral aspects of the disease, so correct differential diagnosis is important.

Wilson's disease (hereditary copper accumulation) may present with parkinsonistic features; young patients presenting with parkinsonism may be screened for this (rare) condition. Essential tremor is often mistaken for Parkinson's disease but usually lacks all features besides tremor.

Pathology

The interaction of dopamine and acetylcholine

The primary symptoms of Parkinson's disease are due to excessive muscle contraction.

Acetylcholine controls muscle contraction via the five cholinergic receptors: m1, m2, m3, m4, and m5. The receptors m1, m3 and m5 are stimulatory. The receptors m2 and m4 are inhibitory. The combined stimulatory effect of m1, m3 and m5 is more powerful in total than the combined inhibitory effect of m2 and m4. So the overall effect of acetylcholine is to stimulate muscle contraction.

Dopamine affects muscle contraction via the five dopamine receptors: D1, D2, D3, D4, and D5. The receptors D2, D3 and D4 are inhibitory. The receptors D1 and D5 are stimulatory. The combined inhibitory effect of D2, D3 and D4 is more powerful in total than the combined stimulatory effect of D1 and D5. So the overall effect of dopamine is to inhibit muscle contraction.

Parkinson's disease consequently occurs when the effect of dopamine is less than that of acetylcholine. Dopamine deficiency rather than acetylcholine excess is normally responsible for this occurring.

Symptoms usually only begin to appear after a reduction down to about 25% of the normal activity of the dopaminergic neurons. The level of dopamine tends to continue to fall slowly over time, with an attendant worsening of symptoms.

Dopamine biosynthesis

The primary fault in Parkinson's disease is that, whatever the cause, there is insufficient dopamine. Dopamine is formed in the dopaminergic neurons by the following pathway:

L-tyrosine → L-dopa → dopamine

The first step is biosynthesised by the enzyme tyrosine 3-monooxygenase * (which is more commonly called by its former name tyrosine hydroxylase). The following is the complete reaction:

L-tyrosine + THFA + O2 + Fe2+ → L-dopa + DHFA + H2O + Fe2+

So for L-dopa formation, L-tyrosine, THFA (tetrahydrofolic acid), and ferrous iron are essential. The activity of this enzyme is often as low as 25% in Parkinson's disease, and in severe cases can be as low as 10%. This indicates that one or more of the elements required for the formation of L-dopa are in insufficient quantities.

The second step in the biosynthesis of dopamine is biosynthesised by the enzyme aromatic L-amino acid decarboxylase * (which is more commonly called by its former name dopa decarboxylase). The following is the complete reaction:

L-dopa + pyridoxal phosphate → dopamine + pyridoxal phosphate + CO2

So for dopamine biosynthesis from L-dopa, pyridoxal phosphate is essential. The activity of the enzyme rises and falls according to how much pyridoxal phosphate there is. The level of this enzyme in Parkinson's disease can also be around 25% or even far less.

Coenzymes involved in dopamine biosynthesis

Besides two enzymes being required for the formation of dopamine from L-tyrosine (L-tyrosine >>> L-dopa >>> dopamine), three coenzymes are also required. Enzymes are substances that will enable a specific chemical reaction to take place in the body. Coenzymes are substances that assist enzymes. Some enzymes (including those involved in dopamine biosynthesis) will not function without coenzymes.

The three coenzymes involved in the formation of dopamine are : THFA (for L-tyrosine to L-dopa), pyridoxal phosphate (for L-dopa to dopamine), and NADH (for the formation of THFA and Pyridoxal phosphate). They are made from vitamins via the following means :

Folic acid → dihydrofolic acid → tetrahydrofolic acid

Pyridoxine → pyridoxal → pyridoxal 5-phosphate (this requires zinc as a cofactor)

Nicotinamide NMN → NAD → NADH (or NADP) → NADPH

G-proteins

In order to relieve Parkinson's disease, dopamine (or dopamine agonists) must stimulate dopamine receptors, which must in turn stimulate the G proteins :

L-tyrosine → L-dopa → dopamine → dopamine receptors (D2, D3, D4) > G proteins

G proteins consist of three parts : alpha - beta - gamma, that are lined to each other. There are three types of beta unit (1, 2, 4), and seven types of gamma unit (2, 3, 4, 5, 7, 10, 11). However, they do not matter much to Parkinson's Disease. What matters to Parkinson's Disease are the alpha subunits, because it is actually these that ultimately relieve (or aggravate) Parkinson's disease. There are five types:

  • G proteins that aggravate Parkinson's disease : Gs 1 alpha
  • G proteins that relieve Parkinson's disease : Gi 1 alpha, Gi 2 alpha, Gi 3 alpha
  • G proteins that have little effect on Parkinson's disease : Go alpha

The sole purpose of dopamine (or dopamine agonists) stimulating dopamine receptors is to cause the alpha subunits (the active part of G proteins) to break away from the rest of the G protein. Without this occurring almost everybody would have Parkinson's disease. Once the alpha part of G proteins is released, via cyclic AMP, it takes the final action in the series of event that leads to the ridding of Parkinson's Disease, which is to inhibit the cells it has effect on.

Neuromelanin

In the cells involved in Parkinson's disease (the dopaminergic neurons) the function is to produce dopamine. In the melanocytes, which are in the skin, the function is to produce the pigment melanin. Melanin is what causes people to suntan. Although they end up with different substances (dopamine and melanin), both of these cells start off with L-tyrosine, and both of them form L-dopa as well:

dopaminergic neurons : L-tyrosine > L-dopa > dopamine

melanocytes : L-tyrosine > L-dopa > melanin

In the dopaminergic neurons, when somebody can not form dopamine, they can accidentally form melanin instead. In the brain it is called neuromelanin because of the different amino acids it is attached to. However, this is not a normal mechanism, and it occurs via a different mechanism from that found in the skin. The formation of neuromelanin in the brain is often claimed to be what happens in healthy brains. Healthy brains are supposed to be darker in the part of the brain called the substantia nigra. However, it is actually due to the biochemical mechanisms not working properly. As not much L-dopa is formed in Parkinson's disease, there isn't much capacity for that L-dopa to accidentally form melanin in the brain. So people with Parkinson's disease can tend to have not much pigment in the part of the brain called the substantia nigra. However, that does not cause a medical problem because melanin is not supposed to be in the brain.

Cell damage

The primary natural means via which cell damage can occur in Parkinson's disease is due to the reaction from L-tyrosine to L-dopa not taking place. The following is what should happen :

L-tyrosine + THFA + O2 + Fe2+ → L-dopa + DHFA + H2O + Fe2+

However, if for example, the THFA in the above reaction is lacking, the following can happen instead :

L-tyrosine + Fe2+ + O2 → L-tyrosine + Fe3+ + O-2 (superoxide anion)

As can be seen there is no L-dopa formed in the faulty reaction, and the superoxide anion is formed instead. The superoxide anion is one of the most highly destructive elements in cells. The formation of L-dopa can also fail to take place if L-tyrosine is deficient.

So the simplest means of preventing cell damage from taking place is to ensure that you have those substances required for the formation of L-dopa, which are L-tyrosine, THFA (which is made from the vitamin folic acid using nicotinamide), and ferrous iron.

Vitamin C and vitamin E have been used to try to help to prevent cell damage in Parkinson's Disease. This is because they are claimed to assist in two enzyme reactions in the brain that get rid of the superoxide anion once it has been formed :

Superoxide dismutase * : 2O-2 + 2H+ → H2O2 + O2

Catalase * : H2O2 → H2O + 1/2 O2

However, the problem with the use of vitamin C and vitamin E in trying to prevent cell damage is that they do nothing at all to prevent the original source of the problem, which is the formation of superoxide anion.

Lewy bodies

Lewy bodies are found in the cytoplasm of neurons. They are often depicted as cellular "rubbish bins" that collect cellular debris. So rather than being the cause of a medical disorder they are a cellular symptom, indicating that cell damage is occurring. They are composed of densely aggregated filaments. These filaments contain ubiquitin and alpha-synuclein. Lewy bodies are often associated with Parkinson's disease. However, they are not unique to Parkinson's disease, as they also occur in several other medical disorders.

Pathophysiology

Most people with Parkinson's disease are described as having idiopathic Parkinson's disease (having no specific cause). There are far less common causes of Parkinson's disease including genetic, toxins, head trauma, and drug induced Parkinson's disease.

Genetic

In recent years, a number of specific genetic mutations causing Parkinson's disease have been discovered, including in certain populations (Contursi). These account for a small minority of cases of Parkinson's disease. Somebody who has Parkinson's disease is more likely to have relatives that also have Parkinson's disease. However, this does not mean that the disorder has been passed on genetically.

Genetic forms that have been identified include:

external links in this section are to OMIM
  • PARK1 (OMIM #168601), caused by mutations in the SNCA gene, which codes for the protein alpha-synuclein. PARK1 causes autosomal dominant Parkinson disease. So-called PARK4 is probably caused by triplication of SNCA.
  • PARK2 (OMIM *602544), caused by mutations in protein parkin. Parkin mutations may be one of the most common known genetic causes of early-onset Parkinson disease. In one study, of patients with onset of Parkinson disease prior to age 40 (10% of all PD patients), 18% had parkin mutations, with 5% homozygous mutations. Patients with an autosomal recessive family history of parkinsonism are much more likely to carry parkin mutations if age at onset is less than 20 (80% vs. 28% with onset over age 40).Patients with parkin mutations (PARK2) do not have Lewy bodies. Such patients develop a syndrome that closely resembles the sporadic form of PD; however, they tend to develop symptoms at a much younger age.

Toxins

The following is a list of toxins that may cause Parkinson's disease or cause symptoms mimicking Parkinson's disease:

Paraquat is a quaternary ammonium herbicide. Other members of this class include diquat, cyperquat, diethamquat, difenzoquat and morfamquat. Pesticides are known to be associated with an increased rate of Parkinson's Disease. Paraquat structurally resembles MPTP and its metabolite MPP+. MPTP and MPP+ are neurotoxic chemicals, that induce Parkinson's Disease in exposed humans. Paraquat might therefore might, as do MPTP and MPP+ inhibit tyrosine hydroxylation, which is essential for the formation of dopamine.

Rotenone is an insecticide that has the poptential to cause Parkinson's disease. Insecticides are also known to affect well water. Rotenone is commonly used in powdered form to treat parasitic mites on chickens and other fowl, and so can be found in poultry. Rotenone is produced by extraction from the roots, seeds, and leaves of certain tropical legumes. Rotenone inhibits tyrosine hydroxylation, which is essential for the formation of dopamine. So rotenone could cause Parkinson's disease by lowering dopamine levels. When given intavenously to mice, rotenone has been demonstrated to cause a model of Parkinson's disease. Rotenone toxicity is caused by complex I inhibition, depletion of cellular ATP, and oxidative damage. These processes cause neuronal loss in midbrain dopaminergic neurons, leading to depletion of dopamine in the brain.

Maneb is a fungicide that contains manganese. The major active element of Maneb is manganese ethylene-bis-dithiocarbamate. Pesticides are known to be associated with an increased rate of Parkinson's disease, so there is a greatly increased likelihood of developing symptoms by people involved in horticulture and agriculture. As Maneb contains manganese it is possible that it causes Parkinson's Disease symptoms via the same means as manganese, which is by inhibiting tyrosine hydroxylation, which is essential for the formation of dopamine. The effects of Maneb are potentiated when there is simultaneous exposure to the pesticide Paraquat.

Manganese can cause manganism, an irreversible neurological disorder similar to Parkinson's disease. Occupational exposures occur mainly in welding, mining as miners are surrounded by manganese dust and airborne manganese particles, alloy production, processing, ferro-manganese operations especially in which manganese ore or manganese compounds are turned into steel, and work with agrochemicals. The towns and communities surrounding the areas of manganese heavy industry could also become affected by exposure to manganese. It is also hypothesized that long-term exposure to the naturally-occurring manganese in shower water also puts people at risk. Manganese inhibits tyrosine hydroxylation, which is essential for the formation of dopamine. So manganese may cause Parkinson's disease by lowering dopamine levels.

MPTP (1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine) is a chemical that may be produced accidentally during illicit manufacture of the recreational drug MPPP, which is a synthetic heroin substitute. The neurotoxicity of MPTP was discovered in 1976 after a chemistry graduate student synthesized MPPP incorrectly and injected the result. It was contaminated with MPTP, and within three days he began exhibiting symptoms of acute Parkinson's disease. It was also developed but unused as a herbicide and was distributed on the streets as a synthetic opioid-like drug. MPTP inhibits tyrosine hydroxylation, which is essential for the formation of dopamine. So MPTP causes acute Parkinson's disease by lowering dopamine levels.

Toluene is a solvent that has been shown to cause or that has been associated with people with Parkinson's disease. Toluene is used as an octane booster in fuel, as a solvent in paints, paint thinners, chemical reactions, rubber, printing, adhesives, lacquers, leather tanning, disinfectants, and to produce phenol and TNT (a component of explosives). It is also used as a raw material for toluene diisocyanate, which is used in the manufacture of polyurethane foams. The precise means of toxicity is not known.

N-hexane, a constituent of solvents has been shown to cause parkinsonism. Most of the n-hexane used in industry is mixed with similar chemicals called solvents. The major use for solvents containing n-hexane is to extract vegetable oils from crops such as soybeans. These solvents are also used as cleaning agents in the printing, textile, furniture, and shoe making industries. Use by chemists. Certain kinds of special glues used in the roofing and shoe and leather industries also contain n-hexane. Several consumer products contain n-hexane, such as gasoline, spot removers, quick-drying glues used in various hobbies, and rubber cement. The precise means is not known.

Carbon disulfide, usually in solvents or pesticides, can cause Parkinson's disease that is associated with other neurological symptoms. The effects can persist for years after exposure to the carbon disulfide has ceased. Potential sources include pesticides used as fumigants, disulfiram (a drug used in the treatment of chronic alcoholism), industrial solvents, solvents used in the production of viscose rayon and cellophane film. Means of toxicity is not established. However, carbon disulphide interferes with pyridoxal 5-phosphate. Pyridoxal 5-phosphate is essential for the formation of dopamine from L-dopa. So carbon disulphide may cause Parkinson's disease symptoms by reducing the formation of L-dopa.

Carbon monoxide toxicity is frequent due to the formation of carbon monoxide by very common means such as gas cookers and exhaust fumes. However, it normally requires severe exposure (e.g. the person going into a coma as a result of the carbon monoxide poisoning) before symptoms of Parkinson's disease develop. Carbon monoxide causes hemoglobin (which transports oxygen) to turn in to carboxyhemoglobin (which does not transport oxygen). Oxygen is required for the formation of L-dopa. So carbon monoxide may cause Parkinson's disease symptoms by interfering with the availability of oxygen to the brain. However, the precise means by which it can cause parkinsonism has still not been proven.

Mercury toxicity is a known cause of symptoms that mimic Parkinson's disease, especially tremor. One of the chief targets of the toxin is the enzyme pyruvate dehydrogenase (PDH). The enzyme is irreversibly inhibited by several mercury compounds, the lipoic acid component of the multienzyme complex binds mercury compounds tightly and thus inhibits PDH. However, the cause of the symptoms of Parkinson's disease is likely to be due to the fact that mercury potently causes the release of dopamine, thereby lowering dopamine levels. Mercury is found in a wide variety of sources: dietary fish intake, ethnic over-the-counter medications, occupational exposures to mercury vapour, possession of dental amalgam fillings, gold production, skin ointment, some soaps.

Cyanide, usually from the consumption of potassium cyanide or sodium cyanide can result in Parkinsonism. Cyanide is also produced by certain bacteria, fungi, and algae, and are found in a number of foods and plants, such as unprocessed cassava, cherry pits, apricot pits, bitter almonds. Hydrogen cyanide is contained in vehicle exhaust and in tobacco smoke,as does burning plastic. Cyanides are also found in gold processing. Cyanide interrupts the electron transport chain in the inner membrane of the mitochondrion. Cyanide also occupies the place of oxygen in hemoglobin (which transports oxygen). Oxygen is required for the formation of L-dopa. So carbon monoxide may cause Parkinson's disease symptoms by interefering with the availability of oxygen to the brain. However, the precise means by which it causes Parkinson's disease has still not been proven.

Copper accumulates in Wilson's disease, which is associated with Parkinson's disease. Although copper may cause symptoms by other means, there do not appear to be published studies in which copper has otherwise caused Parkinson's disease. This may be because copper is not normally formed in to a vapour or dust that can readily be inhaled or consumed. Copper can be found in high quantities in copper mines, copper cooking pots, copper plumbing, very excessive consumption of copper nutritional supplements. Excess copper can cause the formation of a copper-dopamine complex, which leads to the oxidation of dopamine to aminochrome.

Head trauma

Past episodes of head trauma are reported more frequently by sufferers than by others in the population. A methodologically strong recent study found that those who have experienced a head injury are four times more likely to develop Parkinson’s disease than those who have never suffered a head injury. The risk of developing Parkinson’s increases eightfold for patients who have had head trauma requiring hospitalization, and it increases 11-fold for patients who have experienced severe head injury. The authors comment that since head trauma is a rare event, the contribution to PD incidence is slight. They express further concern that their results may be biased by recall, i.e., the PD patients because they reflect upon the causes of their illness, may remember head trauma better than the non-ill control subjects.

Drug-induced

Antipsychotics, which are used to treat schizophrenia and psychosis, can induce the symptoms of Parkinson's disease by lowering dopaminergic activity. Due to feedback inhibition, L-dopa can eventually cause the symptoms of Parkinson's Disease that it initially relieves. Dopamine receptors can also eventually contribute to Parkinson's disease symptoms by increasing the sensitivity of dopamine receptors.

Treatment

Parkinson's disease is a chronic disorder that requires broad-based management including patient and family education, support group services, general wellness maintenance, exercise, and nutrition. At present, there is no cure for PD, but medications or surgery can provide relief from the symptoms.

Levodopa
The most widely used form of treatment is L-dopa in various forms. L-dopa is transfomed into dopamine in the dopaminergic neurons by L-aromatic amino acid decarboxylase (often known by its former name dopa-decarboxylase). However, only 1-5% of L-DOPA enters the dopaminergic neurons. The remaining L-DOPA is often metabolised to dopamine elsewhere, causing a wide variety of side effects. Due to feedback inhibition, L-dopa results in a reduction in the endogenous formation of L-dopa, and so eventually becomes counterproductive.

Carbidopa and Benserazide are dopa decarboxylase inhibitors. They help to prevent the metabolism of L-dopa before it reaches the dopaminergic neurons and are general given as combination preparations of carbidopa/levodopa (co-careldopa BAN) co-careldopa combined L-dopa and carbidopa in fixed ratios in such branded products of Sinemetand Parcopa and Benserazide/levodopa (co-beneldopa BAN) as Madopar. There are also controlled release versions of Sinemet and Madopar that spread out the effect of the L-dopa. Duodopa is a combination of levodopa and carbidopa, dispersed as a viscous gel. Using a patient-operated portable pump, the drug is continuously delivered via a tube directly into the upper small intestine, where it is rapidly absorbed.

Talcopone inhibits the COMT enzyme, thereby prolonging the effects of L-dopa, and so has been used to complement L-dopa. However, due to its side effects, such as possible liver failure is limited in its availability. A similar drug, entacapone, has similar efficacy and has not been shown to cause significant alterations of liver function. Stalevo contains Levodopa, Carbidopa and Entacopone.

Mucuna pruriens, is a natural source of therapeutic quantities of L-dopa.

Dopamine agonists
The dopamine-agonists bromocriptine (Parlodel), pergolide (Permax), pramipexole (Mirapex), ropinirole (Requip), cabergoline (Cabaser), apomorphine (Apokyn), and lisuride (Revanil), are moderately effective. These have their own side effects including those listed above in addition to somnolence, hallucinations and /or insomnia. Dopamine agonists initially act by stimulating some of the dopamine receptors. However, they cause the dopamine receptors to become progressively less sensitive, thereby eventually increasing the symptoms.

Dopamine agonists can be useful for patients experiencing on-off fluctuations and dyskinesias as a result of high doses of L-dopa. Apomorphine can be administered via subcutaneous injection using a small pump which is carried by the patient. A low dose is automatically administered throughout the day, reducing the fluctuations of motor symptoms by providing a steady dose of dopaminergic stimulation. After an initial "apomorphine challenge" in hospital to test its effectiveness and brief patient and caregiver, the primary caregiver (often a spouse or partner) takes over maintenance of the pump. The injection site must be changed daily and rotated around the body to avoid the formation of nodules. Apomorphine is also available in a more acute dose as an autoinjector pen for emergency doses such as after a fall or first thing in the morning.

MAO-B inhibitors
Selegiline (Eldepryl) and rasagiline (Azilect) reduce the symptoms by inhibiting monoamine oxidase-B (MAO-B), which inhibits the breakdown of dopamine secreted by the dopaminergic neurons. By-products of selegiline include amphetamine and methamphetamine, which can cause side effects such as insomnia. Use of L-dopa in conjunction with selegiline has increased mortality rates that have not been effectively explained. Another side effect of the combination can be stomatitis. One report raised concern about increased mortality when MAO-B inhibitors were combined with L-dopa ; however subsequent studies have not confirmed this finding. Unlike other non selective monoamine oxidase inhibitors, tyramine-containing foods do not cause a hypertensive crisis.

Surgical interventions

Treating PD with surgery was once a common practice. But after the discovery of levodopa, surgery was restricted to only a few cases. Studies in the past few decades have led to great improvements in surgical techniques, and surgery is again being used in people with advanced PD for whom drug therapy is no longer sufficient. Deep brain stimulation is presently the most used surgical means of treatment.

Currently under investigation is gene therapy. This involves using a harmless virus to shuttle a gene into a part of the brain called the subthalamic nucleus (STN). The gene used leads to the production of an enzyme called glutamic acid decarboxylase (GAD), which catalyses the production of a neurotransmitter called GABA. GABA acts as a direct inhibitor on the overactive cells in the STN.

GDNF infusion involves, by surgical means, the infusion of GDNF (glial-derived neurotrophic factor)into the basal ganglia using implanted catheters. Via a series of biochemical reactions, GDNF stimulates the formation of L-dopa. GDNF therapy is still in development.

In the future, implantation of cells genetically engineered to produce dopamine or stem cells that transform into dopamine-producing cells may become available. Even these, however, will not constitute cures because they do not address the considerable loss of activity of the dopaminergic neurons.

Nutrients

Nutrients have been used in clinical studies and are widely used by people with Parkinson's disease in order to partially treat Parkinson's disease or slow down its deterioration. The L-dopa precursor L-tyrosine was shown to relieve an average of 70% of symptoms. Ferrous iron, the essential cofactor for L-dopa biosynthesis was shown to relieve between 10% and 60% of symptoms in 110 out of 110 patients. Another complementary approach is Dopavite, a nutritional supplement which contains both of these substances and all the other nutrients required for dopamine formation. However, the efficacy of this nutritional supplement has not been validated in clinical trials.

More limited efficacy has been obtained with the use of THFA, NADH, and pyridoxine—coenzymes and coenzyme precursors involved in dopamine biosynthesis. Vitamin C and vitamin E in large doses are commonly used by patients in order to theoretically lessen the cell damage that occurs in Parkinson's disease. This is because the enzymes superoxide dismutase and catalase require these vitamins in order to nullify the superoxide anion, a toxin commonly produced in damaged cells. However, in the randomized controlled trial, DATATOP of patients with early PD, no beneficial effect for vitamin E compared to placebo was seen

Coenzyme Q10 has more recently been used for similar reasons. MitoQ is a newly developed synthetic substance that is similar in structure and function to coenzyme Q10. However, proof of benefit has not been demonstrated yet.

Physical exercise

Regular physical exercise and/or therapy, including in forms such as yoga, tai chi, and dance can be beneficial to the patient for maintaining and improving mobility, flexibility, balance and a range of motion.

Prognosis

PD is not by itself a fatal disease, but it does get worse with time. The average life expectancy of a PD patient is generally the same as for people who do not have the disease. However, in the late stages of the disease, PD may cause complications such as choking, pneumonia, and falls that can lead to death. The progression of symptoms in PD may take 20 years or more. In some people, however, the disease progresses more quickly. There is no way to predict what course the disease will take for an individual person. One commonly used system for describing how the symptoms of PD progress is called the Hoehn and Yahr scale.

Another commonly used scale is the Unified Parkinson's Disease Rating Scale (UPDRS). This much more complicated scale has multiple ratings that measure mental functioning, behavior, and mood; activities of daily living; and motor function. Both the Hoehn and Yahr scale and the UPDRS are used to measure how individuals are faring and how much treatments are helping them.

With appropriate treatment, most people with PD can live productive lives for many years after diagnosis.

Notable Parkinson's sufferers

One famous sufferer of young-onset Parkinson's is Michael J. Fox, who has written a book about his experience of the disease. The film Awakenings (starring Robin Williams and Robert De Niro and based on genuine cases reported by Oliver Sacks) deals sensitively and largely accurately with a similar disease, postencephalitic parkinsonism.

Other famous sufferers include Pope John Paul II, artist Salvador Dali, evangelist Billy Graham, former US Attorney General Janet Reno, boxer Mohammad Ali, dictators Adolf Hitler, Franco and Mao Zedong, and numerous actors such as Terry Thomas, Kenneth More, Vincent Price and Michael Redgrave.

References

Some of this article contains text from the public domain document at http://www.ninds.nih.gov/disorders/parkinsons_disease/detail_parkinsons_disease.htm

External links

Human diseases | Eponymous diseases | Geriatrics | Neurological disorders | Parkinson's disease

مرض باركنسن | Malaltia de Parkinson | Parkinsonova choroba | Parkinsons sygdom | Parkinson-Krankheit | Νόσος του Πάρκινσον | Enfermedad de Parkinson | Parkinsono | Maladie de Parkinson | 파킨슨씨 병 | Parkinsonova bolest | Penyakit Parkinson | Morbo di Parkinson | מחלת פרקינסון | Penyakit Parkinson | Ziekte van Parkinson | パーキンソン症候群 | Parkinsons sykdom | Choroba Parkinsona | Síndrome de Parkinson | Болезнь Паркинсона | Parkinsonin tauti | Parkinsons sjukdom | โรคพาร์กินสัน | 帕金森氏症

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Parkinson's disease".

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