Transplantation in the treatment of paralysis agitans (Parkinson's disease)

Abstract

Over the past 3 years, there has been great interest in transplantation therapy in the treatment of Parkinson's disease. Following the impressive results reported by Madrazo in the spring of 1987, more than 350 cases of adrenal medullary implantation have been performed worldwide. There has been a significant reduction in "off" time and an increase in "on" time without chorea in 40% of patients having this procedure. The duration of effect is 1 year in half of these cases, with the other half (20% of all patients) still demonstrating significant improvement 3 years after the procedure. The mechanism of the bilateral beneficial improvement is unknown. The survival of adrenal medullary tissue has not been demonstrated at autopsy. It is thought that the mechanism of improvement involves either regenerative sprouting of the remaining dopamine producing neurons as a consequence of the release of neurotrophic factors or an interruption of the striatal pallidal output inhibitory influence of the basal ganglia on the thalamus (or both). Fetal mesencephalic implantation has also been attempted in more than 100 cases worldwide. The improvements when seen are not any more dramatic than those following the best results of adrenal medullary implantation. Graft survival has not been proved; it remains a possibility that interruption of the putaminosubthalamic pallidal pathway or a trophic influence of the tissue provides an alleviation in parkinsonism. The ethical controversy, need for long-term immunosuppression, and difficulty with obtaining tissue of the appropriate age and delivering the appropriate quantity to the putamen have made this technique less than adequate. Newer techniques employing genetic engineering, cultures of adrenal medullary tissue, and encapsulated xenografts are being investigated.