Levodopa is the most effective symptomatic treatment of
Parkinson's disease. However, after an initial period of dramatic benefit, several limitations become apparent including, "
dopa resistant" motor symptoms (postural abnormalities, freezing episodes, speech impairment), "
dopa resistant" non-motor signs (autonomic dysfunction, mood and
cognitive impairment, etc), and/or
drug related side effects (especially
psychosis, motor fluctuations, and
dyskinesias). Motor complications include fluctuations,
dyskinesias, and dystonias. They can be very disabling and difficult to treat. Therefore, strategies should ideally be developed to prevent them. Though mechanisms underlying motor complications are only partially understood, recent work has revealed the importance of pulsatile stimulation of postsynaptic
dopamine receptors and the disease severity. As a result of intermittent stimulation there occurs a cascade of changes in cell signalling leading to upregulation of the
N-methyl-D-aspartate subtype of gamma-aminobutryric
acid-ergic neurones. Modified preparations of
levodopa (
controlled release preparations, liquid
levodopa),
catecholamine-o-
methyltransferase inhibitors,
dopamine agonists, amantidine, and various neurosurgical approaches have been used in the prevention and/or treatment of motor complications. Current management of motor complications is less than satisfactory. With better understanding of the pathogenetic mechanisms, it is hoped that future therapeutic strategies will provide a safer and targeted treatment.