Ben Basger presents 10 points to consider on Parkinson’s Disease…
Parkinson’s disease is much more than a movement disorder!
- Dopamine loss in the substantia nigra, which serves to modify motor control, results in the recognisable core signs of asymmetrical bradykinesia (slowness) and hypokinesia (reduced amplitude) of movement, muscle rigidity (stiffness) and rest tremor.
- The earliest pathological evidence of PD starts in the nervous system of the gut, medulla and olfactory bulb and spreads transneuronally to the midbrain (substantia nigra) and then the cortex. This may explain why non-motor symptoms of PD, such as constipation, hyposmia (reduced ability to smell) and rapid eye-movement sleep disorder often precede the typical motor symptoms, and why cognitive impairment is nearly always found in people with longstanding PD.
- These non-motor symptoms, together with fatigue and depression, may precede diagnosis by as much as 25 years.
- Advancing PD is further complicated by the loss of non-dopaminergic neurones, contributing to disturbances of gait, posture, autonomic nervous function, speech, cognitive function and sleep that may become unresponsive to dopamine. Dopamine replacement alone becomes inadequate.
- Drug-induced parkinsonism due to commonly prescribed dopamine-blocking medications such as antipsychotics (e.g. haloperidol and risperidone) and antiemetics (e.g. metoclopramide and prochlorperazine) should be excluded.
- No treatment has been convincingly shown to slow PD That is, a neuroprotective drug is not available. Drugs treat symptoms ─ they have not been shown to alter the natural course of the disease.
- Although PD is a progressive disorder, deterioration is typically very slow, with considerable individual variability. The time to commence drug treatment for motor symptoms is when they are causing physical or psychological disability. It is a misconception that PD treatment is only effective for a limited time and should be deferred for as long as possible to reserve that benefit.
- All dopaminergic medications can cause nausea, gastrointestinal symptoms, hypotension, drowsiness, cognitive symptoms and impulse control disorders, but these are more common with dopamine agonists (e.g. pramipexole, ropinirole) than with levodopa/dopa decarboxylase inhibitors (LD/DDIs).
- For most patients with PD, motor fluctuations and dyskinesias (abnormal movements) are not disabling and can be adequately managed by manipulating the oral drug regimen
- The incidence of dementia increases with duration of PD. It is characterised by fluctuating cognition and visual hallucinations. Cognitive impairment affects up to 75% of people who have had PD for at least 15 years, although the main risk factor is advancing age.
Our patients may end up on a large variety of medications, apart from treatment for unrelated conditions. Time for a medication review?
Ben Basger is a lecturer and tutor in pharmacy practice, Faculty of Pharmacy, The University of Sydney.