Severity of Parkinson's disease is a risk factor for peak-dose dyskinesia.

Fifty four patients with idiopathic Parkinson's disease receiving levodopa therapy were studied. Thirty three of these patients displayed peak-dose dyskinesia. Neither the duration of Parkinson's disease nor the duration of levodopa therapy discriminated between patients with and patients without peak-dose dyskinesia. Consequently, these criteria could not determine whether the first appearance of peak-dose dyskinesia depends on the duration of Parkinson's disease--a factor that is related to the severity of the disease--or on the duration of levodopa therapy. A subgroup of nineteen patients with unilateral or unequivocally asymmetrical peak-dose dyskinesia was examined 12 hours after withdrawal of levodopa. A levodopa testdose provoked unilateral or unilateral preponderant peak-dose dyskinesia which always involved the most severely affected side and which also happened to be the side of onset of the disease. This demonstrates that the severity of Parkinson's disease is the main risk factor for peak-dose dyskinesia.