|What is Parkinson's Disease?
Parkinson's Disease 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.
Geneticists have, since 1997, found nine different specific
genetic defects, each of which causes the disease in one or
a few families with extraordinarily high incidences of the disease,
but such families are rare.
Symptoms may vary among patients, and additionally may vary
greatly over time in a single patient. However, the primary
- tremor (the best known symptom of PD),
- rigidity (increased tone or stiffness in the muscles),
- bradykinesia (slowness of movement) and akinesia (lack of
- postural instability (failing balance, walking problems)
These additional signs and symptoms are also commonly associated
with Parkinson's Disease:
- 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
- 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);
- 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.
- apathy or abulia: abulia translates from Greek as the absence
or negative of will; apathy is an absence of feeling or desire
- 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.
- sleep disturbances: including 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;
- slowed reaction time; both voluntary and involuntary motor
responses are significantly slowed.
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),
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.