Late-stage Parkinson's Disease is dominated by the loss of autonomy due to motor and non-motor symptoms which can be marginally corrected by medication adjustments. However, controversy exists on the mechanisms underlying the decrease in benefit from L-dopa. So researchers assessed the response to L-dopa in late-stage Parkinson's Disease.
People with late stage Parkinson's Disease and people who had undergone Deep Brain Stimulation underwent an acute L-dopa challenge test. Those people with late stage Parkinson's Disease improved by only 11%, whereas those people who had undergone Deep Brain Stimulation improved by 37%. Rest tremor showed the largest improvement. However, the magnitude of the response to L-dopa was significantly correlated with the severity of dyskinesias in people with late stage Parkinson's Disease. As the Parkinson's Disease symptoms improved, even though the improvement was mild, the dyskinesia worsened. A decrease in L-dopa response is therefore an indicator of the progression of Parkinson's Disease.
Reference : Parkinsonism and Related Disorders  26 : 10-16 (M.Fabbri, M.Coelho, D.Abreu, L.C.Guedes, M.M.Rosa, N.Costa, A.Antonini, J.J.Ferreira)
Complete abstract : http://www.ncbi.nlm.nih.gov/pubmed/26972527