BACKGROUNDThe accuracy of microelectrode-guided localization can make the operation safe and effective, but only experienced neurosurgeons are capable of performing this operation. A good index to identify neuronal discharges between globus pallidus interna and globus pallidus externa is needed. The aim of this research was to establish a good and practical electrophysiologic index to distinguish neuronal discharge in the interior globus pallidus from neuronal discharge in the exterior globus pallidus region of the brain in Parkinson's disease. The effect of neurons having an atypical discharge on successful surgical localization was also quantitatively evaluated.

METHODSThe study included 30 patients with primary Parkinson's disease who underwent pallidotomy between September 2000 and October 2002. During each pallidotomy, the neuronal discharges in the pallidum and its vicinity were recorded. The recorded spikes were used to calculate the frequency, burst index, pause index, and pause ratio of the single-unit discharge. The interior and exterior globus pallidus regions were compared in terms of frequency, burst index, pause index, and pause ratio. The sensitivity, specificity, false-negative ratio, false-positive ratio, and accuracy of those indices were then evaluated.

RESULTSThe values of frequency, burst index, pause index, and pause ratio in the interior globus pallidus were (96 +/- 43) Hz, 2.31 +/- 1.81, 0.05 +/- 0.05, and 0.27 +/- 0.28, respectively, and in the exterior globus pallidus were (59 +/- 27) Hz, 0.88 +/- 0.63, 0.20 +/- 0.14, and 1.54 +/- 1.17, respectively. Use of the four indices to distinguish the two neuron types produced a sensitivity of 0.84, 0.78, 0.77, and 0.93 with a specificity of 0.64, 0.79, 0.88, and 0.87, respectively. The false-positive ratio was 0.36, 0.21, 0.12, and 0.13 and the false-negative ratio was 0.16, 0.22, 0.23, and 0.07 while the accuracy was 0.72, 0.79, 0.80, and 0.90, respectively.

CONCLUSIONSPause ratio is a relatively reliable index to distinguish neuronal discharges between the interior and exterior globus pallidus regions in Parkinson's disease. The effect of neurons with atypical discharge on the successful surgical localization would be reduced to 10% when the pause ratio is used as the index.