Parkinson's Disease and Parkinson's Plus Flashcards
Parkinson’s Disease - Mx
Currently accepted practice in the management of patients with Parkinson’s disease (PD) is to delay treatment until the onset of disabling symptoms and then to introduce a dopamine receptor agonist. If the patient is elderly, levodopa is sometimes used as an initial treatment.
Parkinson’s Disease - Dopamine Receptor Agonists
Dopamine receptor agonists
Eg: Bromocriptine, ropinirole, cabergoline, apomorphine. pramipexole
ergot-derived dopamine receptor agonists (bromocriptine, cabergoline, pergolide*) have been associated with pulmonary, retroperitoneal and cardiac fibrosis. The Committee on Safety of Medicines advice that an echocardiogram, ESR, creatinine and chest x-ray should be obtained prior to treatment and patients should be closely monitored
- Patients should be warned about the potential for dopamine receptor agonists to cause impulse control disorders and excessive daytime somnolence
- Also more likely than levodopa to cause hallucinations in older patients. Nasal congestion and postural hypotension are also seen in some patients
*pergolide was withdrawn from the US market in March 2007 due to concern regarding increased incidence of valvular dysfunction
Parkinson’s Disease - Levodopa
Levodopa:
- Usually combined with a decarboxylase inhibitor (e.g. carbidopa or benserazide) to prevent peripheral metabolism of levodopa to dopamine
- Reduced effectiveness with time (usually by 2 years)
- Unwanted effects: dyskinesia (involuntary writhing movements), ‘on-off’ effect, dry mouth, anorexia, palpitations, postural hypotension, psychosis, drowsiness
- Of no use in neuroleptic induced parkinsonism
Increasing the dose of L-dopa is required when ‘off’ symptoms (bradykinesia, rigidity, freezing) do not respond to the starting dose.
Increasing the frequency of L-dopa, which has a short half-life, is required when patients become ‘off’ in between doses. As the disease progresses the on period after each dose becomes shorter.
Entacapone and selegiline are used as adjuncts to prolong the ‘on’ period after a dose of L-dopa.
Parkinson’s Disease - MAO-B Inhibitors
MAO-B (Monoamine Oxidase-B) inhibitors
e.g. Selegiline
inhibits the breakdown of dopamine secreted by the dopaminergic neurons
Parkinson’s Disease - Amantadine
Amantadine:
- Mechanism is not fully understood, probably increases dopamine release and inhibits its uptake at dopaminergic synapses
- Side-effects include ataxia, slurred speech, confusion, dizziness and livedo reticularis
Parkinson’s Disease - COMT (Catechol-O-Methyl Transferase) inhibitors
COMT (Catechol-O-Methyl Transferase) inhibitors
e. g. Entacapone, tolcapone
- COMT is an enzyme involved in the breakdown of dopamine, and hence its inhibitor may be used as an adjunct to levodopa therapy
- Used in conjunction with levodopa in patients with established PD
Parkinson’s Disease - Antimuscarinics
Antimuscarinics:
- block cholinergic receptors
- now used more to treat drug-induced parkinsonism rather than idiopathic Parkinson’s disease
- help tremor and rigidity
e. g. procyclidine, benzotropine, trihexyphenidyl (benzhexol)
Parkinson’s Disease - Epidemiology
Parkinson’s disease is a progressive neurodegenerative condition caused by degeneration of dopaminergic neurons in the substantia nigra.. This results in a classic triad of features: bradykinesia, tremor and rigidity. The symptoms of Parkinson’s disease are characteristically asymmetrical.
Epidemiology
around twice as common in men
mean age of diagnosis is 65 years
Parkinson’s Disease - Bradykinesia
Bradykinesia
poverty of movement also seen, sometimes referred to as hypokinesia
short, shuffling steps with reduced arm swinging
difficulty in initiating movement
Parkinson’s Disease - Tremor
Tremor
most marked at rest, 3-5 Hz
worse when stressed or tired
typically ‘pill-rolling’, i.e. in the thumb and index finger
Parkinson’s Disease - Rigidity
Rigidity
lead pipe
cogwheel: due to superimposed tremor
Parkinson’s Disease - Other Characteristic Features:
Other characteristic features mask-like facies flexed posture micrographia drooling of saliva psychiatric features: depression is the most common feature (affects about 40%); dementia, psychosis and sleep disturbances may also occur impaired olfaction REM sleep behaviour disorder
Parkinson’s Disease - Autonomic Dysfunction
Patient who presents with hypotensive episodes who is on a PD drug (e.g. Sinemet - Levodopa) = classic non-motor symptom of Parkinsons disease. A significant proportion of patients with PD demonstrate autonomic dysfunction in addition to the classic motor symptoms of rigidity, bradykinesia, resting tremor and postural instability. The patient is likely to demonstrate a significant lying/standing blood pressure difference. Blood pressure lability is a feature of dysautonomia and NO ACTION IS REQUIRED i.e. No pharmacological Mx/IV Fluids (monitor only)
Dopamine Agonists and Impulse Control Disorder - Example Question
A 75-year-old man is referred to you for the management of tremor and mobility issues. On examination, he has a noticeable resting tremor that is worse in the right hand when compared to the left. He also is quite bradykinetic when mobilising and displays mild rigidity. His speech and cognitive function do not appear to be affected. His blood pressure is 125/80 mmHg without any significant postural drop.
You suspect idiopathic Parkinson’s disease. Further history taking reveals that this gentleman has had a previous significant gambling problem which is now well controlled.
Which of the following medications, in particular, should be avoided in this patient?
Rasagiline Levodopa/carbidopa > Pramipexole Entacapone Amantadine
There is an established link between the use of dopamine receptor agonists and serious impulse control disorders. For patients who have a history of habitual behaviours associated with increased risk, this group of medications should be avoided.
PD - Initial Mx of patients <65
Although the treatment of choice should always be individualised to each patient, it is a general rule of starting dopamine agonists such as ropinirole for younger patients under 65, saving L-dopa for later in the disease while reducing the long-term risk of motor complications.
Selegiline is a monoamine oxidase B inhibitor. While it can be a useful adjunct, it does not produce significant functional benefit as a monotherapy and is not commonly used alone for patients with significant motor symptoms.