Ablative therapy for movement disorders. Does thalamotomy alter the course of Parkinson's disease?

Although there is no confirmed evidence that therapy alters the course of Parkinson's disease, some follow-up of patients who have undergone thalamotomy has suggested it might slow or even halt the progress of the disease. A retrospective semiquantitative assessment of 55 patients undergoing bilateral thalamotomy and 31 undergoing unilateral operation confirms the previously held notion that postencephalitic disease or clinical onset below age 40 may progress so slowly as to appear arrested after thalamotomy. Patients left with no tremor and minimal rigidity after completion of unilateral or bilateral surgery, whether their disease is of youthful onset, postencephalitic or not, may also appear to follow stable courses postoperatively. This occurs in patients whose tremor and rigidity have been controlled by bilateral thalamotomy and also in those in whom unilateral tremor and rigidity have been controlled by unilateral surgery in the absence of significant tremor and rigidity on the other side of the body. Possible explanations are discussed.