THE EFFECT OF THE REMOVAL OF THE NUCLEUS DENTATUS ON THE PARKINSONIAN SYNDROME

Parkinsonism for long was dealt with only by neurologists and neuropathologists, but it became of great interest to neurosurgeons when the possibility arose that operation might solve the problem. Interventions were carried out on all those parts of the pyramidal and extrapyramidal system which could be considered on a pathological or experimental basis to be responsible for the development of the symptoms. Since the paper by DelmasMarsalet and van Bogaert (1935) no account has been given of operations performed on the cerebellum. These authors found that after electrical coagulation of the dentate nucleus there was a slight diminution of rigidity whereas tremor became more marked. They stopped this intervention on account of complications arising in one of their patients, and as far as we know neither they nor others have since carried out operations of that kind. In the surgery of extrapyramidal diseases attention has been directed rather to interventions on the pallidothalamic system; and indeed some authors carrying out experimental research work considered that Parkinsonian tremor was of cerebellar origin (Carrea, Reissig, and Mettler, 1947, 1955). In their opinion Parkinsonian tremor is a result of a cerebellar lesion and further intervention on the cerebellum only increases it. However, according to Fulton (1949), after the isolated removal of the nucleus dentatus tremor (cerebellar intention) is of a transitory character and becomes only more marked after the removal of the nucleus globosus and emboliformis. We therefore decided to operate on the cerebellum in certain cases in order to diminish the Parkinsonian syndrome. First, it seemed to us that hypotonia resulting from a cerebellar lesion caused by removal of the dentate nucleus might be expected to reduce rigidity but that no conclusions could be drawn from the published data concerning the question of tremor; either improvement or worsening of this symptom might follow the operation. Secondly, it has become evident that surgical interventions on the pallido-thalamic system had not been so successful that we should not seek new operative methods to solve the problem. Again, among the successful operations on the thalamus there were some in the course of which the thalamic part of the dentato rubro-thalamic tract was disconnected. In these cases, tremor and rigidity diminished more markedly than after operations on the pallidum (Bravo and Cooper, 1959). The possible disadvantages of causing a cerebellar syndrome had to be taken into consideration. We expected, however, that after the removal of one nucleus dentatus the disturbing side-effects would show a tendency to recover well. On the other hand, if we wanted to achieve prolonged results the efferent tracts of the cerebellum should be disconnected as extensively as possible in spite of possible prolonged side-effects. Also it was doubtful whether disconnecting the dentate nucleus in an intact extrapyramidal system would have the same effects as the operation in a pathologically defective one. In two of our three patients we attempted a stereotactic operation on the pallido-thalamic system before interfering with the cerebellum. In one case we failed to carry out the procedure, and in the second case it did not prove very successful and the effects were not sufficiently lasting for it to seem worth while to repeat the operation.