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.