Status of fetal tissue transplantation for the treatment of advanced Parkinson disease

In the first double-blind, placebo-controlled randomized study of fetal tissue transplantation for the treatment of patients with advanced Parkinson disease (PD), investigators found that implanted dopaminergic tissue can produce measurable improvement in young PD in the absence of medication (that is, the “off” state). The results of the study, however, also highlighted several serious limitations of transplantation. In the group of older patients in the study (in the typical age range of individuals afflicted with PD) no improvement was derived from the implant despite positron emission tomography–documented scan evidence that the graft survived and produced dopamine. Patients in the study were selected because they experienced motor fluctuations, and the transplant did not improve dyskinesias or the time required to remain “on” medication for any subgroup of patients, including young patients. Five of 33 implant-treated patients developed involuntary movements (dyskinesias or dystonia) that could not be eliminated by reducing antiparkinsonian medications. These included four patients with the best responses to transplantation. Finally, some sham-operated patients experienced a dramatic placebo effect lasting at least 1 year, which justified the controversial sham surgery. The authors believe that these problems must be solved before fetal tissue transplantation can be considered a therapeutic option for PD.