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Neurology - Parkinson's Disease
Whiteboard Animation Transcript
with Raed Joundi, MD & Elizabeth Slow, MD
medskl.com/Mod...
Parkinson’s disease (or PD) is the second most common neurodegenerative disorder after Alzheimer’s disease, and affects 1% of individuals over the age of 65.
It is classified as a hypokinetic movement disorder and occurs due to degeneration of dopaminergic neurons that project from the substantia nigra in the midbrain to the basal ganglia. The initial precipitant of neuronal death is unknown, and by the time symptoms emerge, between 50-80% of dopaminergic neurons have already degenerated.
The cardinal features of PD are:
Tremor,
Rigidity,
Akinesia/bradykinesia, and
Postural instability,
easily remembered with the mnemonic TRAP.
The most essential feature for diagnosis of PD is bradykinesia, which is characterized by a reduction in both speed and amplitude of voluntary movement. This is most striking during repetitive movements like finger tapping, where taps are slowed and become progressively smaller in amplitude, or writing, where letter size decreases across the page, also known as micrographia.
Bradykinesia is also manifested as a loss of facial expression (or hypomimia), reduced vocal volume (or hypophonia), and slowing with a variety of other activities including walking, dressing, and turning in bed.
The tremor in PD is typically a unilateral, rhythmic, resting tremor between 4-6 Hz, and can classically start as a ‘pill-rolling’ tremor of the thumb and forefinger.
Rigidity is an involuntary increase in muscle tone present throughout the range of movement, and can be tested by passively moving the arm, neck, or leg. If rigidity is smooth and consistent throughout it is called ‘lead-pipe’ rigidity. If, however, there is a ratchet-like quality, it is called cogwheeling, which is thought to be due to rigidity superimposed on an underlying tremor.
Parkinsonism also causes characteristic gait abnormalities: stooped posture, small shuffling steps, reduced arm swing, and freezing, make sure to watch out for falls!
PD is treated with levodopa, which is a precursor of dopamine, the neurotransmitter that is deficient in PD. In fact, an excellent response to levodopa in a patient with asymmetric tremor-predominant parkinsonism is supportive of the diagnosis of PD.
It is important to keep in mind that PD is the most common form of parkinsonism, but patients may develop parkinsonism from other causes, including medications such as anti-psychotics, other degenerative disorders such as multiple-system atrophy, and Wilson’s disease which causes copper deposition in the basal ganglia.
23 окт 2024
