Parkinson's disease

Parkinson's disease (paralysis agitans or PD) is a neurodegenerative disease of the substantia nigra, an area in the basal ganglia of the brain. The disease was first recognised and its symptoms documented in 1817 in An Essay on the Shaking Palsy by the British physician Dr James Parkinson; the associated biochemical changes in the brain of patients were identified in the 1960s. Some gene defects associated with the disease were identified only recently; others remain unknown.

The disease involves a progressive disorder of the extrapyramidal system, which controls and adjusts communication between neurons in the brain and muscles in the human body. It also commonly involves depression and disturbances of sensory systems.

Parkinson's disease is widespread, with a prevalence estimated between 100 and 250 cases per 100,000 in North America; globally prevalence estimates range from a low of 15 per 100,000 in China to a high of 657 per 100,000 in Argentina. Because prevalence rates can be affected by socio-economically driven differences in survival, incidence is a more sensitive indicator: rates have ranged from 1.5 per 100,000 in China to a high of 14.8 per 100,000 in Finland. [BC Medical Journal Volume 43, Number 3, April 2001, 133-137 Epidemiology of Parkinson’s disease Benjamin C.L. Lai, MD, MSc, and Joseph K.C. Tsui, MD, FRCP(UK), FRCPC]

About 2% of the population develops the disease some time during life, though the mean age at onset is 58-60. Symptoms usually begin in the upper extremities, and are usually unilateral (one-sided) or asymmetrical at onset.

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, presumably because the pattern of brain cell pathology is individual.

Motor symptoms
The cardinal symptoms are: (The mnemonic TRAP (Tremor; Rigidity; Akinesia/bradykinesia; Postural instability) can be used to remember these symptoms.)
 * tremor: 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.  Foot dystonia can be a presenting symptom of PD, especially in younger patients.
 * 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 death.
 * Other motor symptoms:
 * fatigue (up to 50% of cases);
 * masked facies (a mask-like face also known as hypomimia), with infrequent blinking(http://jnnp.bmjjournals.com/cgi/content/full/64/3/320);
 * 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:
 * depression: occurs in 40-70% of cases; 20% of depression cases are major depressive disorder; severity and persistance of depression is positively associated with executive dysfunction and dementia;
 * anxiety or panic attacks Note: 70% of individuals with parkinson's disease diagnosed with pre-existing depression go on to develop anxiety; 90% of Parkinson's disease patients with pre-existing anxiety subsequently develop depression);
 * apathy or abulia: abulia translates from Greek as the absence or negative of will; apathy is an absence of feeling or desire

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, interpeting 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.

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:
 * oily skin and seborrheic dermatitis;
 * urinary incontinence, typically in later disease progression
 * constipation and gastricdysmotility: severe enough to endanger comfort and even health
 * altered sexual function: characterized by profound impairment of sexual arousal, behavior, orgasm, and drive is found in mid and late parkinson disease. Current data addresses male sexual function almost exclusively.

Other notes
Symptoms usually only begin to appear after about 80% of the dopamine in the brain has been lost. More recent data based on PET scans suggests that symptoms may occur when 50-60% of dopaminergic neurons are lost. The level of dopamine will continue to fall slowly over time, with an attendant worsening of symptoms.

It is an incapacitating disease, disturbing important human functions and ultimately substantially reducing quality of life. As in many neurologic diseases, psychological complications are often extremely serious and require the patient's family members and relatives to pay keen attention to the emotional fragility that usually follows the emergence of the disease; indeed, the depression which often results is seen by many as one of the worst aspects of the disease.

Fairly effective medication for the movement difficulties of Parkinson disease have been available for some time, but the neuropsychiatric aspects of the disease, especially depression and anxiety, are more recently characterized, less well understood, and often less adequately treated. As patients become more disabled, they become more dependent on care from others to perform all manner of tasks, from eating and bathing to monitoring and taking medication. Helping individuals with chronic disability and psychiatric comorbidity to maintain purposeful engagement with life takes a physical and emotional toll on caregivers, who may consequently experience illness and depression themselves.

Cases of PD are reported at all ages, though it is quite rare in people younger than 30 and the average age at which symptoms begin is 58-60; the risk of developing it substantially increases with age. 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 and men are affected slightly more often than women.

Differential diagnosis
The differential diagnosis for a patient presenting with Parkinsonian symptoms is:
 * Idiopathic Parkinson's disease
 * Essential tremor (ET): tremor is typically associated with posture-holding and voluntary movement, and absent at rest. A head tremor suggests ET; a lip or chin tremor is more typical of PD.
 * Parkinson plus syndromes (see below)
 * Secondary parkinsonism due to drugs, toxins, stroke, head trauma, or hydrocephalus

Parkinson's tremors differ from essential tremors in that the latter are posture or action tremors, have bilateral tremors involving the hands, head and voice, and are alcohol responsive. In contrast, Parkinson's tremors are rest tremors, and usually start unilaterally.

Imaging
SPECT with ([123I]FP-CIT) or PET with 18F-fluorodopa are the two imaging modalities used to assess dopamine transporter density and the integrity of nigrostriatal pathways in the central nervous system. Currently (2005) FP-CIT is widely used in Europe for the diagnostic workup of Clinically Uncertain Parkinsonian Syndromes; although it is not available in the United States.

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


 * Multiple System Atrophy (MSA)
 * Shy-Drager Syndrome (SDS)
 * Striatonigral degeneration (SND)
 * Olivopontocerebellar Atrophy (OPCA)
 * Progressive Supranuclear Palsy (PSP)
 * Corticobasal Degeneration (CBD)

Some people include Dementia with Lewy Bodies (DLB) as one of the 'Parkinson-Plus' syndromes. Although Idiopathic Parkinson 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 Demnentia (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 haldol. Administration of such drugs is dangerous, even lethal, Additionally, the cholinesterase inhibiting medications have shown preliminary efficacy in treating the cognitive, psychiatric, and behavioral aspcects of the disease, so correct differential diagnosis is important.

Distribution of Neural Degeneration in the Brain
The most striking gross pathologic abnormality in Parkinson disease (PD) is loss of pigmentation in an area of the midbrain called the substantia nigra pars compacta. This depigmentation corresponds to loss of neuromelanin-containing, dopamine-producing neurons. In the past, most of the symptoms of PD have been attributed to neuron loss in this region.

Pathologic abnormalities have also been noted in other regions of the brain. The Dutch neuropathologist Heiko Braak has described a progressive, upward involvement of brain structures, starting in the dorsal motor nucleus of the vagus nerve in the brainstem, progressing over time to involve midbrain, limbic, and finally neocortical neurons. Based on this work, Braak and his colleagues have proposed the following neuropathological staging system for PD:

Pre-clinical (no symptoms of PD). Neural degeneration confined to brainstem.
 * Stage 1: Dorsal motor nucleus of the vagus nerve
 * Stage 2: Locus ceruleus and raphe nucleus

Clinical (symptomatic). Progressive involvement of midbrain, limbic structures, and cortex. 
 * Stage 3: substantia nigra, amygdala, basal forebrain (esp. nucleus basalis of Meynert), ventral tegmental area, among others
 * Stage 4: stria terminalis, intralaminar thalamic nuclei, insular cortex, temporal mesocortex, anterior cingulate gyrus
 * Stage 5: neocortical higher-order sensory association areas and prefrontal fields
 * Stage 6: first-order sensory association areas, premotor fields, primary neocortical fields

Although there is still some degree of controversy surrounding this staging system, the broad areas of brain involved do seem to account for the myriad motor and non-motor symptoms found in PD. Braak and colleagues have embarked on the work of systematically correlating pathologic stage of PD with clinical manifestations. Recently, his team published work correlating the incidence and severity of dementia with pathologic stage of PD.

The Lewy Body
Historically, the Lewy body has been the microscopic pathologic hallmark of Parkinson disease. Lewy bodies are found in the cytoplasm of neurons, and are composed of densely aggregated filaments. These filaments contain ubiquitin and alpha-synuclein.

Patients with parkin mutations (PARK2, see below) 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. Whether the Lewy body itself causes neurodegeneration; or whether it is a protective response by damaged neurons is the focus of current research.

Pathophysiology: A Complex Interaction Between Genetics and Environment
The cause of neuron loss Parkinson's disease is not fully understood(idiopathic). There are, however, many theories.

Genetic
Parkinson disease (PD) is thought to be caused by some combination of genetic and environmental factors. Up to one third of PD cases run in families. The rest are apparently sporadic cases. Inheritance may be Mendelian, i.e., autosomal recessive, autosomal dominant, or x-linked. Mitochondrial inheritance has been postulated but not proven. Most familial cases, however, follow no clear inheritance pattern.

An affected individual is three to four times more likely than an unaffected individual to have a close relative with PD. Having a first degree relative (parent or sibling) with PD doubles or triples an individual's risk of PD relative to the general population. 

In recent years, a number of specific genetic mutations causing PD have been discovered. However, these account for a minority of PD cases.

Genetic forms that have been identified include:
 * 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).
 * PARK3 (OMIM %602404), mapped to 2p, autosomal dominant, only described in a few kindreds.
 * PARK5, caused by mutations in the UCHL1 gene (OMIM +191342) which codes for the protein ubiquitin carboxy-terminal hydrolase L1
 * PARK6 (OMIM #605909), caused by mutations in PINK1 (OMIM *608309) which codes for the protein PTEN-induced putative kinase 1.
 * PARK7 (OMIM #606324), caused by mutations in DJ-1
 * PARK8 (OMIM #607060), caused by mutations in LRRK2 which codes for the protein dardarin. In vitro, mutant LRRK2 causes protein aggregation and cell death, possibly through an interaction with parkin.  LRRK2 mutations, of which the most common is G2019S, cause autosomal dominant Parkinson disease, with a penetrance of nearly 100% by age 80.  G2019S is the most common known genetic cause of Parkinson disease, found in 1-6% of U.S. and European PD patients.  It is especially common in Ashkenazi Jewish patients, with a prevalence of 29.7% in familial cases and 13.3% in sporadic.
 * PARK12 (OMIM %300557), maps to the X chromosome

Mitochondrial DNA mutations may also play a role in PD. Dysfunction in mitochondrial Complex I has been found in autopsy specimens and platelets from PD patients. Certain mitochondrial DNA haplogroups have been associated with increased susceptibility for disease. However, no kindred has been identified that demonstrates a clear pattern of mitochondrial inheritance.

Toxins
One theory holds that the disease may result in many or even most cases from the combination of a genetically determined vulnerability to environmental toxins along with exposure to those toxins. This hypothesis is consistent with the fact that Parkinson's disease is not distributed homogenously throughout the population: rather, its incidence varies geographically. The toxins most strongly suspected at present are certain pesticides and industrial metals. MPTP is used as a model for Parkinson's as it can rapidly induce parkinsonian symptoms in human beings and other animals, of any age. Other toxin-based models employ PCBs, paraquat  (a herbicide) in combination with maneb, a fungicide  rotenone  (an insecticide), and specific organochlorine pesticides including dieldrin   and lindane. Numerous studies have found an increase in Parkinson disease in persons who consume rural well water; researchers theorize that water consumption is a proxy measure of pesticide exposure. In agreement with this hypothesis are studies which have found a dose-dependent  an increase in PD in persons exposed to agricultural chemicals.

Almost all of the PD-causing toxins act on the mitochondrial complex I of the electron transfer chain, and sporadic PD cases have been found to have a partial loss of activity of this enzyme complex. Studies in cybrids have found that mitochondrial DNA, rather than nuclear DNA, is responsible for the dysfunction. Most recently, microheteroplasmic mutations in one of the mitochondrial complex I genes, ND5, were found to be sufficient to diagnose sporadic PD correctly in 27 out of 28 cases. While additional studies are needed, mitochondrial microheteroplasmic mutations may be the cause of the majority of PD cases.

However, the ubiquity of agricultural chemical exposures makes it difficult to gauge the true extent of the problem. In the current state of knowledge about the origins of the disease, it appears that family history of the disease and (especially) multiple episodes of head-trauma-induced unconsciousness increase individual risk more than does pesticide exposure, but research is continuing.

Head trauma
Past episodes of head trauma are reported more frequently by sufferers than by others in the population. A methodologically strong recent study [Bower 2003] 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. While emotional or psychological trauma can precipitate the initial symptoms or aggravate existing symptoms, this is probably not the actual cause of the disorder. However, psychological trauma during periods of developmental susceptibility cannot be definitely excluded as triggers.

Other Associations


 * Prior history of an affective disorder

Loss of dopamine-secreting cells
The symptoms of Parkinson's disease result from the loss of dopamine-secreting (dopaminergic) cells and subsequent loss of melanin, secreted by the same cells, in the pars compacta region of the substantia nigra (literally "black substance"). These neurons project to the striatum and their loss leads to alterations in the activity of the neural circuits within the basal ganglia that regulate movement, in essence an inhibition of the direct pathway and excitation of the indirect pathway.

The direct pathway facilitates movement and the indirect pathway inhibits movement, thus the loss of these cells leads to a hypokinetic movement disorder. The lack of dopamine results in increased inhibition of the ventral lateral nucleus of the thalamus, which sends excitatory projections to the motor cortex, thus leading to hypokinesia.

There are four major dopamine pathways in the brain; the nigrostiatal 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. Disruption of dopamine along the non-striatal pathways is the likely explantion for much of the neuropsychiatric pathology associated with Parkinson's disease.

Brain cells producing other brain chemicals such as GABA, norepinephrine, serotonin and acetylcholine exhibit damage in Parkinson's disease, accounting for some of the wide array of symptoms.It is not known whether this damage is a primary disease process, or secondary to loss of normal dopaminergic stimulation.

The mechanism by which the brain cells in Parkinson's are lost appears to center on an abnormal accumulation of the protein alpha-synuclein bound to ubiquitin in the damaged cells.alpha-synuclein-ubiquitin complex cannot be directed to the proteosome. This protein accumulation forms proteinaceous cytoplasmic inclusions called Lewy bodies. Excessive accumulations of iron, which are toxic to nerve cells, are also typically observed in conjunction with the protein inclusions.

The precise mechanism whereby aggregates of alpha-synuclein damage the cells is not known. The aggregates may be merely a normal reaction by the cells as part of their effort to correct a different, as-yet unknown, insult. It does appear that alpha-synuclein aggregation is enhanced by the presence of dopamine and the byproducts of dopamine production. Based on this mechanistic hypothesis, a transgenic mouse model of Parkinson's has been generated by introduction of human wild-type &alpha;-synuclein into the mouse genome under control of the platelet-derived-growth factor-&beta; promoter.

Treatment
The treatment of Parkinson's disease mainly relies on replacing dopamine with levodopa (L-DOPA) or mimicking its action with dopamine agonists such as pramipexole, ropinirole, pergolide or bromocriptine. Discovered as a Parkinson's treatment by Arvid Carlsson, levodopa is a dopamine precursor that is transfomed into dopamine by dopa-decarboxylase, present in the basal ganglia in the brain as well as other tissues, e.g., the retina. Levodopa is almost always supplemented with carbidopa or benserazide, dopa-decarboxylase inhibitors which prevent levodopa from being prematurely converted into dopamine in the adrenal glands or other peripheral tissues. This leaves more levodopa to reach the brain and allows a reduced dosage to produce the same effect on the central nervous system, thus reducing the peripheral side effects, which included protracted nausea, before the formulation l-dopa with carbidopa.

The most frequent side effects of these dopaminergic drugs are nausea, sleepiness, dizziness, involuntary writhing movements and visual hallucinations. Despite these side effects, treatment of a Parkinson's patient with these two drugs can result a striking "return to life" in the eyes of the patient's family and doctors, to the point that the patient's illness is imperceptibe to most observers.

However, progression is inexorable, and the drugs are not effective forever. A point is reached where the drugs only work for periods of a few hours ("on" periods) which are sandwiched between longer interval during which the drugs are partially or completely ineffective ("off periods").

With protracted use of dopamine replacement, the intervals of partial effectiveness are characterized by writhing, choreiform movements --dyskinesia-- that are involuntary, can be very disruptive of normal movement and communication, and can physically exhaust patients. "On", "off", and "dyskinesia" are motor fluctuations: Almost all patients who use dopamine replacement therapy develop motor fluctuations within ten years, younger patients more quickly than older. Despite their somewhat bizarre appearance, a majority of patients prefer a state of dyskinetic "on" to immobilized "off", possibly because the off state is so subjectively paralyzing, and often accompanied by panic.

Therapy for Parkinson disease typically requires an evolving regimen of multiple medications, each calibrated to individual physiology and symptoms. Medicating to control the side effects of other medications contributes to polypharmacy: Amantadine hydrochloride, anticholinergics and COMT inhibitors tolcapone or entacapone are sometimes prescribed to reduce the motor fluctuations that are a consequence of dopaminergic therapy. Tolcapone should be used with extreme caution because of the possibility of liver failure; Entacapone has not been shown to cause significant alterations of liver function.

Foods rich in proteins can reduce the uptake of levodopa, because some amino acids compete with levodopa for cellular receptor sites. This can usually be dealt with by offsetting medication and meal times: consuming the majority of required proteins towards the evening allows patients to use dopamine medication more effectively during the morning and mid-day when mobility is more critical.

While these therapies are a good attempt at treating the symptoms, they are not a cure--they do not attack the underlying cause of the disease which is a loss of dopamine producing neurons. Only a therapy that addresses the underlying causes of dopamine cell pathology and permits their replacemt is likely to constute a cure.

Regular physical exercise and/or therapy are beneficial to the patient and essential for maintaining and improving mobility, flexibility, balance and a range of motion, and for a better resistance against many of the secondary symptoms and side effects. There is increasing evidence that exercise is both neuroprotective against the development of Parkinson's disease, and also ameliorative of both severity of symptoms, and also possibly of progression. "Alternative" exercise modalities such as yoga, tai chi, and dance may also hold promise as rehabilitation therapies, due to their integration of movement, thought, feeling, and sensory experience. Exercise has also been shown to effectively improve mild-moderate/ depression,

Surgical interventions are an active area of current research, and deep brain stimulation is presently the most popular and effective such treatment. 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 widespread loss of several different types of cells in the brain and even for the dopamine-producing cells, do not re-establish all of the original connections with neighboring brain cells. A true cure will have to detect the earliest signs of the disorder before they cause important symptoms and will intervene in the process that damages the brain cells in the first place.

Dopamine deficiency is central, but deficits of serotonin, norepinephrine, and acetylcholine are also typical. The depression and anxiety states that predominate when serotonin and norepinephrine are deficient are often treated with selective serotonine reuptake inhibitors (SSRIs) like Paxil, Zoloft, or Celexa; there is emerging evidence that the SSNRI (selective serotonin and norepinephrine reuptake inhibitor) Effexor may be particularly effective in Parkinson's disease because it augments two deficient neurotransmitters. Amphetimine-like drugs (Ritalin, Concerta) are being prescribed with increasing frequency to treat the Attention Deficit Disorder (ADD)-like attention problems that are almost universal in Parkinson's disease. Finally, there is emerging evidence to suggest that drugs that inhibit the reuptake of acetylcholine, developed as treatments for Alzheimer's dementia, may also improve memory and executive function in Parkinson's disease.

The patient and physicians are confronted with the behavioral and cognitive consequences of disruptions in at least five neurotransmitters; in addition to the four above, GABA is also disrupted. The inevitable cost, risk, and sheer unpleasantness of such complex medication regimens drives both doctors and patients to advocate for better and more comprehensive therapies.

The best evidence is that analytic and synthetic reasoning are relatively spared, even in advancing Parkinson's disease. However, the evidence that executive function impairment begins early and is progressive is growing rapidly. Coupled with the observation that more than 70 percent of Parkinson disease patients meet the criteria for at least one psychiatric diagnosis (most commonly anxiety or depression, with apathy also significant), the picture that emerges is one of considerable neuropsychological disability in individuals with preserved reasoning and awareness.

Because reasoning and awareness are operative, most patients can and should participate in their own care. This is correct from a legal and moral perspective of respect for the dignity and autonomy of individual patients, but it is also good medical practice. The formation of a "therapeutic alliance" between the patient and the physician ensures the optimal exchange of information, and amplifies the effectiveness of medical interventions.

The liberty to exercise preferences, even in regard to seemingly trivial details, has been shown to preserve the intellectual and emotional integrity of very physically compromised individuals. Patients have both a legal and a moral right to participate in their own care to the fullest extent possible.

The cumulative prevalence of dementia (substantially disabling defects in memory and reasoning)in Parkinson disease is still being debated, but the estimates range from 40 to 80 percent; more careful analysis seems to support the higher estimates. . With this fact in mind, patients, families, caregivers and medical personnel should work together to outline clear and pragmatically possible ways to preserve the dignity and choices of patients even when they cannot speak clearly for themselves.

Secondary parkinsonism
Secondary parkinsonism (or briefly parkinsonism) is a term used for a symptom constellation that is similar to that of Parkinson's disease but is caused by other disorders or medications. Major reasons for secondary parkinsonism are stroke, encephalitis, narcotics, toxins such as manganese or carbon monoxide poisoning, traumatic brain injury, and normal pressure hydrocephalus.

There are other idiopathic (of unknown cause) conditions as Parkinson's disease that may cause parkinsonism. In these conditions the problem is not the deficient production of dopamine but the inefficient binding of dopamine to its receptors located on globus pallidus.

Parkinson's and death
Parkinson's does not by itself cause death, but since the disease may affect the respiratory system, sufferers may eventually contract pneumonia and die. Swallowing difficulties may lead to aspiration of food, causing aspiration pneumonia (a specific form of pneumonia caused by gastric acid, food and digestive tract bacteria). Immobility may increase susceptibility to infection. Onset of dementia doubles the odds of death; depression more than doubles the odds ratio. However, people may live for 20 to 30 years with the condition.

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; the state of the art in treatment remains roughly the same as it was at the time of the events depicted, the 1960s, although patients with postencephalitic parkinsonism lose benefit from their medication far faster than do patients with Parkinson's disease. Other famous sufferers include Pope John Paul II, former US Attorney General Janet Reno, and dictator Adolf Hitler (who may have developed Parkinsonism as a consequence of poisonous gas exposures in the trenches of WWI).