[Treatment of abnormal movements by thalamic lesions]

Thalamic targets in the treatment of involuntary movements include the lateral and usually the intermediary ventral nuclei. Destruction of their afferents in Forel's fields provides the same therapeutic result but the size of the lesion must then be very small due to the proximity of essential structures, particularly corpus Luysi. Efficacy of treatment depends partly on the aetiology of the involuntary movement (and thus from the indication for surgery) and also on the technical possibilities of electrophysiologic mapping. The true dystonic element of the involuntary movement is usually little improved whereas tremors of all types are improved or suppressed. Essential tremor, familial or not, of large amplitude and very disabling, is an ideal indication for stereotaxic surgery when it presents as intention tremor. In Parkinson's disease, the treatment is effective against tremor and rigidity but akinesia is unaltered and the progressive course of the disease uninterrupted. Indications for surgery have become rare since the availability of L-dopa, perhaps too rare for the slowly progressive forms with predominant tremor poorly relieved by dopa-therapy, surgery has a curative and probably preventive effect on the involuntary movements of limbs induced by this treatment. Suppression of post-traumatic tremor and that due to multiple sclerosis is dependent on various factors: electrophysiologic precise mapping of the target since "electrical silences or holes" exist that disturb or prevent collection of evoked potentials or spike activity; multiple neurologic lesions that may be worsened by an additional thalamic lesion; finally residual cerebellar disturbance unmasked by the suppression of tremor, a poor "functional" result despite a good operative result.(ABSTRACT TRUNCATED AT 250 WORDS)