Efficacy of levodopa therapy on motor function after posteroventral pallidotomy for Parkinson’s disease

To the Editor:

We read with interest the article by Uitti et al. on the efficacy of levodopa therapy on motor function in 41 patients with complicated PD submitted to microelectrode-guided pallidotomy.1 The authors found no significant change in the latency, duration, or magnitude of clinical response after administration of an acute challenge of levodopa. However, it is difficult to understand how the magnitude of the clinical response remained unchanged after surgery. This pharmacologic parameter is defined as the difference between basal “off” and best “on” Unified Parkinson’s Disease Rating Scale (UPDRS) motor scores. Many reports confirm that pallidotomy provides marked contralateral amelioration of parkinsonian symptoms, and after surgery patients reported less recognizable “on-off” fluctuations.

Current ideas about the pathophysiologic basis of motor fluctuations suggest that the magnitude of the motor response is the key factor in the development of the wearing-off phenomenon.2 The improvement in motor fluctuations after pallidotomy is most likely due to a reduction in the magnitude of the motor response as a result of reduced severity of the parkinsonian signs and symptoms in the operated side. Indeed, Uitti et al. noted that the mean motor “off” score after pallidotomy was improved by 10 points (48.7 versus 38.6). The best motor “on” score was also improved, although to a lesser degree (24.6 versus 20.1). Despite this improvement in both scores, the magnitude of the motor response should be reduced after surgery because the degree of improvement in the “off” score is bigger than that obtained in the best “on” score. Other groups, despite methodologic differences, have found a significant reduction in the magnitude and an increase in the duration of the clinical benefit after acute levodopa and apomorphine challenges.3-5

We evaluated six patients with PD who underwent pallidotomy. The magnitude was reduced …