Parkinson disease: the facts
WHAT IS PARKINSON DISEASE?
Parkinson disease (PD) is a chronic, progressive, incurable, and disabling degenerative condition of the
nervous system. Parkinson's disease occurs when nerve cells, or neurons, in an area of the brain known
as the substantia nigra die or become impaired. Normally, these neurons produce an important brain
chemical known as dopamine. Dopamine is a chemical messenger responsible for transmitting signals
between the substantia nigra and the next "relay station" of the brain, the corpus striatum (Figure 1).
Brain dopamine has a critical role in motivation and movement. Bursts of dopamine release are critical in
the planning, initiation and maintenance of purposeful movements.
Figure 1: Dopamine projections of the brain.
Parkinson disease (PD) is a chronic, progressive, incurable, and disabling degenerative condition of the
nervous system. Parkinson's disease occurs when nerve cells, or neurons, in an area of the brain known
as the substantia nigra die or become impaired. Normally, these neurons produce an important brain
chemical known as dopamine. Dopamine is a chemical messenger responsible for transmitting signals
between the substantia nigra and the next "relay station" of the brain, the corpus striatum (Figure 1).
Brain dopamine has a critical role in motivation and movement. Bursts of dopamine release are critical in
the planning, initiation and maintenance of purposeful movements.
Figure 1: Dopamine projections of the brain.
Loss of dopamine results in abnormal nerve firing patterns within the brain that cause impaired
movement. Studies have shown that most Parkinson's patients have lost 60 to 80 percent or more of the
dopamine-producing cells in the substantia nigra by the time symptoms appear. The dopamine loss is
accompanied by the microscopic appearance of Lewy bodies in brain cells. Lewy bodies are unusual
deposits or clumps of various proteins including alpha-synuclein (Figure 2). Work on the staging of Lewy
pathology in PD indicates that the disease begins in the medulla and the olfactory complex, and ascends
in a predictable sequence to involve the entire neocortex (Braak et al. 2004). Recent studies have shown
that people with PD also have loss of the nerve endings that produce the neurotransmitters
noradrenaline and serotonin. These chemical messengers are related to dopamine, and are involved in
parts of the nervous system that control many automatic functions of the body, such as pulse and blood
pressure. Their loss might help explain several of the non-motor features seen in PD, including fatigue
and abnormalities of blood pressure regulation.
Figure 2: Lewy body within nerve cell
movement. Studies have shown that most Parkinson's patients have lost 60 to 80 percent or more of the
dopamine-producing cells in the substantia nigra by the time symptoms appear. The dopamine loss is
accompanied by the microscopic appearance of Lewy bodies in brain cells. Lewy bodies are unusual
deposits or clumps of various proteins including alpha-synuclein (Figure 2). Work on the staging of Lewy
pathology in PD indicates that the disease begins in the medulla and the olfactory complex, and ascends
in a predictable sequence to involve the entire neocortex (Braak et al. 2004). Recent studies have shown
that people with PD also have loss of the nerve endings that produce the neurotransmitters
noradrenaline and serotonin. These chemical messengers are related to dopamine, and are involved in
parts of the nervous system that control many automatic functions of the body, such as pulse and blood
pressure. Their loss might help explain several of the non-motor features seen in PD, including fatigue
and abnormalities of blood pressure regulation.
Figure 2: Lewy body within nerve cell
WHAT ARE THE SYMPTOMS AND HOW IS THE DISEASE DIAGNOSED?
In life, there is no reliable test that can distinguish PD from other conditions that have similar clinical
presentations and diagnosis can be challenging. In older patients, PD can present with general functional
decline and non-specific symptoms. History and examination are pivotal for diagnosis.
Tremor of the fingers, hands, arms or jaw affects ¾ of patients, is unilateral at onset, occurs at rest and
improves with purposeful movement. Stiffness of the muscles (rigidity) makes movement difficult and may
cause pain and cramps. Slowness of movement (akinesia) affects small and precise movements first (such
as writing or fastening buttons). Later, involvement of larger muscles leads to difficulty getting out of a
chair or starting walking. Loss of balance causes unsteadiness when walking, turning or rising from a
chair and can lead to falls and may necessitate the use of walking aids.
Slowness of movement and stiffness of the muscles almost always respond (sometimes dramatically) to
treatment with levodopa. However, illnesses other than PD (e.g., drug-induced parkinsonism, multiple
system atrophy, autosomal recessive juvenile parkinsonism) may also improve significantly with
dopaminergic drugs. Conversely, specific signs such as early falls, poor response to levodopa, symmetry
of motor manifestations, lack of tremor, and early autonomic dysfunction suggest an alternate diagnosis.
Predictive factors for more rapid motor progression, nursing home placement, and shorter survival time
in PD include older age at onset of PD, associated comorbidities, presentation with rigidity and akinesia,
and reduced responsiveness to medications (Suchowersky et al. 2006).
In life, there is no reliable test that can distinguish PD from other conditions that have similar clinical
presentations and diagnosis can be challenging. In older patients, PD can present with general functional
decline and non-specific symptoms. History and examination are pivotal for diagnosis.
Tremor of the fingers, hands, arms or jaw affects ¾ of patients, is unilateral at onset, occurs at rest and
improves with purposeful movement. Stiffness of the muscles (rigidity) makes movement difficult and may
cause pain and cramps. Slowness of movement (akinesia) affects small and precise movements first (such
as writing or fastening buttons). Later, involvement of larger muscles leads to difficulty getting out of a
chair or starting walking. Loss of balance causes unsteadiness when walking, turning or rising from a
chair and can lead to falls and may necessitate the use of walking aids.
Slowness of movement and stiffness of the muscles almost always respond (sometimes dramatically) to
treatment with levodopa. However, illnesses other than PD (e.g., drug-induced parkinsonism, multiple
system atrophy, autosomal recessive juvenile parkinsonism) may also improve significantly with
dopaminergic drugs. Conversely, specific signs such as early falls, poor response to levodopa, symmetry
of motor manifestations, lack of tremor, and early autonomic dysfunction suggest an alternate diagnosis.
Predictive factors for more rapid motor progression, nursing home placement, and shorter survival time
in PD include older age at onset of PD, associated comorbidities, presentation with rigidity and akinesia,
and reduced responsiveness to medications (Suchowersky et al. 2006).
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Dr Andrew H Evans
Flemington Neurology
Flemington Neurology
Suite 105
55 Flemington Road
North Melbourne, Victoria 3051
admin@flemingtonneurology.com
t: 03 9348 9381 f: 03 9329 1473
55 Flemington Road
North Melbourne, Victoria 3051
admin@flemingtonneurology.com
t: 03 9348 9381 f: 03 9329 1473