 |
Parkinson's disease is an idiopathic, slowly progressive, degenerative CNS disorder characterized by resting tremor, muscular rigidity, slow and decreased movement, and postural instability. Diagnosis is clinical. Treatment is with levodopa plus carbidopa, other drugs, and, for refractory symptoms, surgery.
Parkinson's disease affects about 0.4% of people > 40 yr, 1% of people ≥ 65 yr, and 10% of people ≥ 80 yr. The mean age at onset is about 57 yr. Rarely, Parkinson's disease begins in childhood or adolescence (juvenile parkinsonism).
Parkinsonism refers to symptoms that are similar to those of Parkinson's disease but caused by another condition.
Etiology
and Pathophysiology
Synuclein is a presynaptic neuronal and glial cell protein, which can form insoluble fibrils in Lewy bodies. Although there are rare cases of Parkinson's disease without Lewy bodies, the pathologic hallmark of Parkinson's disease remains synuclein-filled Lewy bodies in the nigrostriatal system. However, synucleinopathy can occur in many other parts of the nervous system, including the dorsal motor nucleus of the vagus nerve, basal nucleus of Meynert, hypothalamus, neocortex, olfactory bulb, sympathetic ganglia, and myenteric plexus of the GI tract. Lewy bodies appear in a temporal sequence, and many experts believe that Parkinson's disease is a relatively late development in a systemic synucleinopathy, which may also include Lewy body dementia. Patients with Parkinson's disease may also have Alzheimer's disease. Parkinson's disease, Lewy body dementia, and Alzheimer's disease share several features (see Delirium and Dementia: Dementia); further research is needed to clarify their relationship to each other, including the relative contributions of synucleinopathy.
In Parkinson's disease, pigmented neurons of the substantia nigra, locus ceruleus, and other brain stem dopaminergic cell groups are lost. Loss of substantia nigra neurons, which project into the caudate nucleus and putamen, depletes dopamine in these areas.
A genetic predisposition is likely, at least in some cases. About 15 to 20% of patients have a family history of Parkinson's disease. Several abnormal genes have been identified. Inheritance is autosomal dominant for some genes and autosomal recessive for others.
Symptoms and Signs
In most patients, the disease begins insidiously.
A resting tremor of one hand is often the first symptom. The tremor is characterized as follows:
Usually, the hands, arms, and legs are most affected, in that order. The jaw, tongue, forehead, and eyelids may also be affected, but not the voice. Tremor may become less prominent as the disease progresses.
Rigidity develops without tremor in many patients. When a clinician moves a rigid joint, sudden, rhythmic jerks due to variations in the intensity of the rigidity occur, producing a ratchet-like effect (cogwheel rigidity).
Slow movements (bradykinesia) are typical as rigidity progresses. Movement also becomes decreased (hypokinesia) and difficult to initiate (akinesia).
Rigidity and hypokinesia may contribute to muscular aches and sensations of fatigue. The face becomes masklike, with an open mouth, drooling, and reduced blinking. Early on, patients may appear depressed because facial expression is lacking and movements are decreased and slowed. Speech becomes hypophonic, with characteristic monotonous, stuttering dysarthria. Hypokinesia and impaired control of distal musculature cause micrographia (writing in very small letters) and make activities of daily living increasingly difficult. Without warning, voluntary movement, including walking, may suddenly halt (called freezing).
Postural
instability develops, resulting in gait abnormalities. Patients have difficulty starting to walk, turning, and stopping; the gait becomes shuffling with short steps, and the arms are held flexed to the waist and do not swing with the stride. Steps may inadvertently quicken, and patients may break into a run to keep from falling (festination). A tendency to fall forward (propulsion) or backward (retropulsion) when the center of gravity is displaced results from loss of postural reflexes. Posture becomes stooped.
Dementia can occur.
Sleep
disorders are common. Insomnia may result from nocturia or from the inability to turn in bed. Rapid eye movement (REM) sleep behavior disorder may develop; in it, violent bursts of physical activity occur during REM sleep. Sleep deprivation may contribute to depression, exacerbate cognitive impairment, or cause excessive daytime sleepiness.
Neurologic symptoms
unrelated to parkinsonism commonly develop because synucleinopathy occurs in other areas of the central, peripheral, and autonomic nervous systems. It may have the following effects:
Seborrheic dermatitis is also common.
Postencephalitic
parkinsonism causes forced, sustained deviation of the head and eyes (oculogyric crises), other dystonias, autonomic instability, depression, and personality changes.
Diagnosis
Diagnosis is clinical. Parkinson's disease is suspected in patients with characteristic unilateral resting tremor, decreased movement, or rigidity. The tremor disappears (or attenuates) during finger-to-nose coordination testing.
During the neurologic examination, patients cannot perform rapidly alternating or rapid successive movements well. Sensation and strength are usually normal. Reflexes are normal but may be difficult to elicit because of marked tremor or rigidity. Patients cannot suppress eye closure when the frontal muscle is tapped between the eyes (glabellar reflex; if persistent, called Myerson's sign).
Slowed and decreased movement due to Parkinson's disease must be differentiated from decreased movement and spasticity due to lesions of the corticospinal tracts. Unlike Parkinson's disease, corticospinal tract lesions cause paresis (weakness or paralysis), preferentially in distal antigravity muscles, and cause extensor plantar responses (Babinski's sign). Spasticity due to corticospinal tract lesions increases muscle tone and deep tendon reflex responses; muscle tone increases in proportion to rate and degree of stretch placed on a muscle until resistance suddenly melts away (clasp-knife phenomenon). Rigidity in Parkinson's disease differs because resistance does not change through the entire range of motion (moving the limb is similar to bending a lead pipe).
Diagnosis is confirmed by the presence of other characteristic signs (eg, infrequent blinking, lack of facial expression, impaired postural reflexes, characteristic gait abnormalities). Tremor without other characteristic signs suggests early disease or another diagnosis. In the elderly, decreased spontaneous movements or a short-stepped (rheumatic) gait may result from depression or dementia; such cases may be difficult to distinguish from Parkinson's disease.
To differentiate Parkinson's disease from secondary parkinsonism, clinicians note whether levodopa results in dramatic improvement, suggesting Parkinson's disease. Causes of parkinsonism can be identified by the following:
Treatment
Many oral drugs are commonly used to relieve symptoms of Parkinson's disease (see Table 3: Movement and Cerebellar Disorders: Some Commonly Used Oral Antiparkinsonian Drugs ). Traditionally, levodopa is the first drug used. However, some experts believe that early use of levodopa hastens development of adverse effects and inconsistency of drug response; they prefer to delay levodopa, particularly in younger patients, if possible and use anticholinergic drugs, amantadine , or dopamine agonists first if drug treatment is necessary. Levodopa is then delayed until symptoms interfere with daily activities despite use of other treatments.
Doses are often reduced in the elderly. Drugs that cause or worsen symptoms, particularly antipsychotics, are avoided.
Levodopa:
Levodopa, the metabolic precursor of dopamine , crosses the blood-brain barrier into the basal ganglia, where it is decarboxylated to form dopamine . Coadministration of the peripheral decarboxylase inhibitor carbidopa prevents levodopa catabolism, thus lowering the levodopa dosage requirements and minimizing adverse effects. Levodopa is most effective at relieving bradykinesia and rigidity, although tremor is often substantially reduced. Mildly affected patients who take levodopa may return to nearly normal, and bedbound patients may become ambulatory.
Levodopa has central adverse effects; occasional hallucinations or delirium occurs, most often in the elderly and patients with dementia. The dose that causes dyskinesias tends to decrease as treatment continues. In some patients, the lowest dose that reduces parkinsonian symptoms also causes dyskinesias.
Dosage of carbidopa/levodopa is increased every 4 to 7 days as tolerated until maximum benefit is reached. Adverse effects may be minimized by increasing the dose gradually and by giving the drug with or after meals; however, high-protein meals may impair absorption of levodopa. If peripheral adverse effects predominate, increasing the amount of carbidopa may help. Most patients with Parkinson's disease require 400 to 1000 mg/day of levodopa in divided doses q 2 to 5 h. A dissolvable immediate-release oral form of carbidopa/levodopa can be taken without water; this form is useful for patients who have difficulty swallowing. Doses are the same as for immediate-release carbidopa/levodopa .
Occasionally, levodopa must be used to maintain motor function despite levodopa-induced hallucinations or delirium. Psychosis can sometimes be treated with oral quetiapine or clozapine ; these drugs aggravate parkinsonian symptoms much less than other antipsychotics (eg, risperidone , olanzapine ) or not at all. Haloperidol should be avoided. Quetiapine can be started at 25 mg once/day or bid and increased in 25-mg increments q 1 to 3 days up to 800 mg/day as tolerated. Use of clozapine is limited because agranulocytosis occurs in 1% of patients. When clozapine is used, the dose is 12.5 to 50 mg once/day to 12.5 to 25 mg bid. CBC is done weekly for 6 mo and every 2 wk thereafter.
After 2 to 5 yr of treatment, most patients experience fluctuations in their response to levodopa (on-off effect). Whether dyskinesias and the on-off effect result from levodopa or the underlying disease is controversial. Eventually, the period of improvement after each dose shortens, and drug-induced dyskinesias result in swings from intense akinesia to uncontrollable hyperactivity. Traditionally, such swings are managed by keeping the levodopa dose as low as possible and using dosing intervals as short as q 1 to 2 h. Alternative methods include adjunctive use of dopamine -agonists, controlled-release levodopa/carbidopa, COMT and/or MAO inhibitors, and amantadine .
Amantadine:
This drug is useful as monotherapy for early, mild parkinsonism in 50% of patients and later can be used to augment levodopa's effects. It may augment dopaminergic activity, anticholinergic effects, or both. If used as monotherapy, amantadine often loses its effectiveness after several months. Amantadine may ameliorate dyskinesias secondary to long-term use of levodopa.
Dopamine agonists:
These drugs directly activate dopamine receptors in the basal ganglia. Oral drugs include bromocriptine , pramipexole , and ropinirole .
Oral dopamine agonists can be used as monotherapy but, as such, are rarely sufficient for more than a few years. They may be useful at all stages of the disease. Using these drugs early in treatment, with small doses of levodopa, may delay emergence of dyskinesias and on-off effects, possibly because dopamine agonists stimulate dopamine receptors longer than levodopa does. This type of stimulation is more physiologic and better preserves the receptors. Dopamine agonists are particularly useful in later stages when response to levodopa decreases or on-off effects are prominent.
Rotigotine is available as a skin patch and can be used in a similar fashion to the oral agonists.
Adverse effects may limit use of dopamine agonists. Reducing the levodopa dose may minimize adverse effects of dopamine agonists. Agonists can cause compulsive gambling, hypersexuality, or overeating in 1 to 2% of patients, requiring a change in drug or a reduction in dose. Bromocriptine is rarely used because cardiac valvular fibrosis and pleural fibrosis are concerns. Pergolide , another dopamine agonist, was recalled because it increases risk of cardiac valvular fibrosis.
Apomorphine is an injectable dopamine agonist used as rescue therapy when off effects are severe. Onset of action is rapid (5 to 10 min), and duration is short (60 to 90 min). Apomorphine 2 to 6 mg sc can be given up to 5 times/day as needed. A 2-mg test dose is given first to check for orthostatic hypotension. BP is checked in the standing and supine positions before treatment and 20, 40, and 60 min afterward. Other adverse effects are similar to those of other dopamine agonists. Nausea can be prevented by starting trimethobenzamide 300 mg po tid 3 days before apomorphine and continuing it for the first 2 mo of treatment.
Selective
monoamine oxidase type B (MAO-B) inhibitors:
Selegiline inhibits one of the 2 major enzymes that break down dopamine in the brain, thereby prolonging the action of each dose of levodopa. In some patients with mild on-off effects, selegiline helps prolong levodopa's effect. Used initially as monotherapy, selegiline can delay the initiation of levodopa by about 1 yr. Selegiline may slow progression of Parkinson's disease by potentiating residual brain dopamine in early disease or by reducing oxidative metabolism of brain dopamine . A dose of 5 mg po bid does not cause hypertensive crisis (sometimes triggered by consuming tyramine in foods, such as some cheeses, during MAO inhibitor therapy); this adverse effect is common with nonselective MAO inhibitors, which block A and B isoenzymes. Although virtually free of adverse effects, selegiline can potentiate levodopa-induced dyskinesias, mental and psychiatric adverse effects, and nausea, requiring reduction in the levodopa dose. Selegiline is also available in a formulation designed for buccal absorption (zydis- selegiline ).
Rasagiline , a new MAO-B inhibitor that is not metabolized to amphetamine, is effective and well-tolerated in early and late disease. Whether rasagiline 's effects are purely symptomatic or also neuroprotective is unknown.
Anticholinergic
drugs:
These drugs can be used as monotherapy in early disease and later to supplement levodopa. Commonly used anticholinergic drugs include benztropine and trihexyphenidyl . Antihistamines with anticholinergic effects (eg, diphenhydramine 25 to 50 mg po bid to qid, orphenadrine 50 mg po once/day to qid) are occasionally useful for treating tremor. Anticholinergic tricyclic antidepressants (eg, amitriptyline 10 to 150 mg po at bedtime), if used for depression, may be useful as an adjunct to levodopa. Doses of anticholinergic drugs are increased very slowly. Adverse effects are particularly troublesome in the elderly; if possible, they should not be given anticholinergic drugs.
Catechol O-methyltransferase (COMT)
inhibitors:
These drugs (eg, entacapone , tolcapone ) inhibit the breakdown of dopamine and therefore appear to be useful adjuncts to levodopa. A combination of levodopa, carbidopa, and entacapone can be used. For each dose of levodopa taken, 200 mg of entacapone is given, to a maximum of 200 mg 8 times/day. Tolcapone , a potent MAO inhibitor, is less commonly used because of rare reports of liver toxicity.
|
Table 3
|
| | |
|
Some Commonly Used Oral
Antiparkinsonian Drugs
|
|
Drug
|
Starting Dose
|
Average Daily Dose
|
Usual Dose Range
|
Major Adverse Effects
|
|
Dopamine precursors
|
|
Levodopa
|
500–1200 mg*
|
1200 mg
|
500–6000 mg (total daily), in divided doses
|
Central: Drowsiness, confusion, orthostatic hypotension, psychotic disturbances, nightmares, dyskinesia
Peripheral: Nausea, anorexia, flushing abdominal cramping, palpitations
|
|
Carbidopa/levodopa 25/100, 10/100, or 25/250 mg (immediate-release or dissolvable)
|
25/100 mg tid
|
25/100 mg tid to 25/100 mg 6 times/day
|
25/100 mg tid to 25/250 mg 8 times/day
|
|
Carbidopa/levodopa 25/100 or 50/200 mg (controlled-release)
|
25/100 mg bid
|
50/200 mg tid to qid
|
75/300–600/2400 mg (total daily), in divided doses
|
|
Antiviral drug
|
|
Amantadine
|
100 mg once/day
|
100 mg bid
|
100–200 mg bid
|
Confusion, urinary retention, leg edema, elevated intraocular pressure, livedo reticularis
|
|
Dopamine agonists
|
|
Bromocriptine
†
|
1.25 mg bid
|
10–40 mg once/day
|
1.25–40 mg once/day
|
Nausea, vomiting, somnolence, orthostatic hypotension, dyskinesia, confusion, hallucinations, delirium, psychosis
|
|
Pramipexole
|
0.125 mg tid
|
0.5–1 mg tid
|
1.5 mg tid
|
|
Ropinirole
|
0.25 mg tid
|
3–4 mg tid
|
0.25–8 mg tid
|
|
Anticholinergic drugs‡
|
|
Benztropine
|
0.5 mg at night
|
1 mg bid
|
0.5 mg at night to 2 mg tid
|
Dry mouth, urinary retention, constipation, blurred vision
Particularly in the elderly, confusion, delirium, impaired thermoregulation due to decreased sweating
|
|
Trihexyphenidyl
|
1 mg tid
|
2 mg tid
|
2–5 mg tid
|
|
Monoamine oxidase-B (MAO-B) inhibitors
|
|
Rasagiline
|
0.5 mg once/day
|
1–2 mg once/day
|
1–2 mg once/day
|
Nausea, insomnia, somnolence, edema
|
|
Selegiline
§
|
5 mg once/day
|
5 mg bid
|
5 mg bid
|
Possible potentiation of nausea, insomnia, confusion, and dyskinesias secondary to levodopa
|
|
Catechol O-methyltransferase (COMT) inhibitor
|
|
Entacapone
||
|
200 mg with each dose of levodopa
|
800 mg once/day
|
800–1600 mg once/day
|
Dyskinesias, nausea, confusion, hallucinations, diarrhea, discoloration of urine
|
|
*Levodopa 1200 mg once/day is equivalent to carbidopa/levodopa 25/100 mg tid.
†Rarely used because cardiac valvular fibrosis and pleural fibrosis are concerns.
‡Should be used cautiously in the elderly.
§Also available in a formulation designed for buccal absorption (zydis- selegiline ).
||Also available in a triple combination tablet (carbidopa, levodopa, and entacapone ).
|
|
Surgery:
If drugs are ineffective and disease is advanced, surgery is considered. For patients with levodopa-induced dyskinesias, deep brain stimulation of the subthalamic nucleus or globus pallidus interna is often recommended. For patients with tremor only, stimulation of the ventralis intermediate nucleus of the thalamus is sometimes recommended; however, because most patients also have other symptoms, stimulation of the subthalamic nucleus, which relieves tremor as well as other symptoms, is usually preferable.
Physical measures:
Maximizing activity is a goal. Patients should do daily activities to the extent possible. If they cannot, physical or occupational therapy, which may involve a regular exercise program, may help condition them physically. Therapists may teach patients adaptive strategies and help them make appropriate adaptations in the home (eg, installing grab bars to reduce the risk of falls).
Because the disease, antiparkinsonian drugs, and inactivity can lead to constipation, patients should consume a high-fiber diet, exercise when possible, and drink adequate amounts of fluids. Dietary supplements (eg, psyllium) and stimulant laxatives (eg, bisacodyl 10 to 20 mg po once/day) can help.
Parkinsonism
Parkinsonism refers to symptoms that are similar to those of Parkinson's disease but caused by another condition.
Parkinsonism results from disorders other than Parkinson's disease, drugs, or exogenous toxins (see Table 4: Movement and Cerebellar Disorders: Some Causes of Parkinsonism). The mechanism is blockage of or interference with dopamine 's action in the basal ganglia. The most common cause is ingestion of drugs that block dopamine receptors (eg, phenothiazine, thioxanthene, butyrophenone, antipsychotic drugs, reserpine ).
|
Table 4
|
| | |
|
Some Causes of Parkinsonism
|
|
Cause
|
Comments
|
|
Neurodegenerative disorders
|
|
Amyotrophic lateral sclerosis-parkinsonism-dementia complex of Guam
|
Responds poorly to antiparkinsonian drugs
|
|
Corticobasal ganglionic degeneration
|
Begins asymmetrically, usually after age 60
Causes cortical and basal ganglia signs, often with apraxia, dystonia, myoclonus, and alien limb syndrome (movement of a limb that seems independent of the patient's conscious control)
Causes immobility after about 5 yr and death after about 10 yr
Responds poorly to antiparkinsonian drugs
|
|
Dementia (eg, Alzheimer's disease, chromosome 17-linked frontotemporal dementias, diffuse Lewy body dementia)
|
Parkinsonism often preceded by dementia with prominent memory loss
|
|
Multiple system atrophy
|
May include prominent autonomic dysfunction
May have predominantly cerebellar features
Often causes early falls and balance problems
Responds poorly to antiparkinsonian drugs
|
|
Progressive supranuclear palsy
|
First manifests with gait and balance problems
Causes progressive ophthalmoparesis starting with downward gaze
Responds poorly to antiparkinsonian drugs
|
|
Spinocerebellar ataxia 3
|
Responds poorly to antiparkinsonian drugs
|
|
Other disorders
|
|
Cerebrovascular disease
|
Manifests with rigidity and bradykinesia or akinesia (akinetic-rigid syndrome) that predominantly involves the lower extremities, with prominent gait disturbance
Rarely responds to antiparkinsonian drugs
|
|
Brain tumors near the basal ganglia
|
Manifests with hemiparkinsonism (ie, restricted to one side of the body)
|
|
Repeated traumatic brain injury
|
Often causes dementia (described as punch-drunk)
|
|
Hydrocephalus
|
Usually, normal-pressure hydrocephalus; rarely, obstructive hydrocephalus
|
|
Hypoparathyroidism
|
Causes calcification of the basal ganglia; may cause chorea and athetosis
|
|
Viral (eg, West Nile) encephalitis, infectious or postinfectious autoimmune
|
Can cause parkinsonism transiently during the acute phase or, rarely, permanently (eg, postencephalitic parkinsonism after the epidemic of encephalitis lethargica in 1915–1926)
In postencephalitic parkinsonism: Forced, sustained deviation of the head and eyes (oculogyric crises); other dystonias; autonomic instability; depression; and personality changes
|
|
Drugs
|
|
Antipsychotics
|
Can cause reversible* parkinsonism
|
|
Meperidine analog (MPTP)†
|
Can cause sudden, irreversible parkinsonism
Occurs in IV drug users
|
|
Methyldopa
|
Can cause reversible* parkinsonism
May be dose-dependent or related to the patient's susceptibility (risk factors include older age and female sex)
|
|
Metoclopramide
|
Same as for methyldopa
|
|
Reserpine
|
Same as for methyldopa
|
|
Lithium , long-term use
|
Same as for methyldopa
|
|
Toxins
|
|
Carbon monoxide
|
Can cause irreversible parkinsonism
|
|
Methanol
|
As contaminated moonshine, can cause hemorrhagic necrosis of the basal ganglia
|
|
Manganese
|
Can cause parkinsonism with dystonia and cognitive changes when toxicity is chronic
Usually occupation-related
|
|
*When drugs are withdrawn, symptoms usually resolve within a few weeks, although they may persist for months.
†MPTP results from unsuccessful attempts to produce meperidine for illicit use.
MPTP = N-methyl-1,2,3,4-tetrahydropyridine.
|
|
Parkinsonism causes the same symptoms as Parkinson's disease (eg, resting tremor, rigidity, bradykinesia, postural instability (see above).
Diagnosis
To differentiate Parkinson's disease from secondary parkinsonism, clinicians note whether levodopa results in dramatic improvement, suggesting Parkinson's disease. Causes of parkinsonism can be identified by the following:
Treatment
The cause is c |
