A prospective study of the cumulative incidence and course of restless legs syndrome in de novo patients with Parkinson’s disease during chronic dopaminergic therapy

The authors report the cumulative incidence of Restless Legs Syndrome (RLS) over a 3 years follow-up period in 92 de novo Parkinson’s disease patients under chronic dopaminergic therapy and the clinical course of the sensory-motor disorder over 12 months as from its onset. The overall cumulative incidence of RLS was found by 15.3 %, i.e. 14 incident cases, and by 11.9 %, i.e. 11 incident cases, after the exclusion of possible “secondary” forms of the disorder. These figures are higher than those reported in general population in Germany (Study of Health in Pomerania), confirming our previous findings of incidence rate of the disorder. At the end of the 3 years follow-up period the prevalence of “current” RLS was significantly higher than that previously found in drug naïve Parkinson’s disease patients and in controls, supporting the view that RLS emerging in the course of chronic dopaminergic therapy is the main determinant of the co-morbid association with Parkinson’s disease. During the 12 months period of observation the RLS showed a frequency of occurrence of 6.08 episodes per month on average and a remittent clinical course was prevailing in the 11 incident cases, with a significant frequency decrease in the second as compared to the first 6 months, i.e. 3.26 versus 8.9 episodes per month, and none of the patients developed augmentation in the same period. It is hypothesized that the remittent course could be due to long-term adaptation (downregulation) of the hypersensitive post-synaptic dopamine receptors in the spinal cord to a continuous dopaminergic stimulation, possibly coupled with compensatory up-regulation of pre-synaptic dopamine re-uptake mechanism, in the patients in which the hypothalamic A11 area, site of origin of the dopamine-mediated diencephalo-spinal pathway, is involved in the neurodegenerative process.