Neurology -- Correspondence for de Bie et al., 58 (7) 1008-1012

Correspondence published:

Reply to Letter to the Editor: Johannes D. Speelman, Rob M. A. deBie (17 July 2002)

Morbidity and mortality following pallidotomy in Parkinson’s disease: A systematic review: Valerie Biousse, Nancy J. Newman (17 July 2002)

Reply to Letter to the Editor 17 July 2002

Johannes D. Speelman
Academic Medical Center Amsterdam The Netherlands,
Rob M. A. deBie
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Re: Reply to Letter to the Editor

j.d.speelman{at}amc.uva.nl Johannes D. Speelman, et al.

The objective of our systematic review was to estimate the frequency of morbidity and mortality due to unilateral and bilateral pallidotomy.[1] We agree with Drs. Biousse and Newman that properly designed studies are mandatory for the evaluation of the frequency of complications. Therefore, we used strict inclusion criteria.
The study of Biousse et al. was not included because their report only mentions the effects of pallidotomy on the visual fields and not the other adverse effects. [2, 3]
In the study of Biousse et al. two of the 40 patients (5%, 95% CI 0.6 to 17.0%) had difficulties due to a visual field defect following pallidotomy. [2] One patient was clearly aware of the visual field defect and a second patient complained of difficulty while reading. We found a frequency of 2.4%, which is in agreement with their findings (difference 2.6%, 95% CI -4.4 to 9.6%). Biousse et al. concluded that the frequency of post-pallidotomy visual field defects is low and that when visual field defects do occur, they are usually not severe or functionally limiting. [2]
References:
1. de Bie RMA, de Haan RJ, Schuurman PR, Esselink RAJ, Bosch DA, Speelman JD. Morbidity and mortality following pallidotomy in Parkinson’s disease. A systematic review. Neurology 2002;58:1008-1012.
2. Biousse V, Newman NJ, Carroll C, et al. Visual fields in patients with a posterior GPi pallidotomy. Neurology 1998;50:258-265.
3. Baron MS, Vitek JL, Bakay RAE, et al. Treatment of advanced Parkinson’s disease by posterior GPi pallidotomy: 1-year results of a pilot study. Ann Neurol 1996;40:355-366.

Morbidity and mortality following pallidotomy in Parkinson’s disease: A systematic review 17 July 2002

Valerie Biousse
Emory Eye Center,
Nancy J. Newman
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Re: Morbidity and mortality following pallidotomy in Parkinson’s disease: A systematic review

vbiouss{at}emory.edu Valerie Biousse, et al.

We read with interest the article on complications of pallidotomy in Parkinson’s disease (PD). [1] In an attempt to present the frequency of morbidity and mortality associated with pallidotomy, the authors reviewed only original studies providing data on consecutive cases of pallidotomy. There are several problems with such a selection process. First of all, the authors’ use of strict criteria for selection of “relevant studies”, although necessary and laudatory to some degree, has eliminated 91% of the articles published between 1992 and 2000. Their choice of articles to include in this review seems somewhat arbitrary.
Recently we published in Neurology a prospective study of visual field defects in 40 consecutive patients who underwent pallidotomy for PD. [2] Even though this study corresponds to the inclusion criteria detailed by the authors in their Methods section (reporting of clinical data in PD, reporting of original data, unequivocal description of morbidity and mortality, and reporting of unselected consecutive cases), it was not included among the 27 studies reviewed in their article.
Furthermore, since most studies did not systematically look for all the complications evaluated in this review, it is likely that some of these complications were overlooked, and, therefore, were underestimated in the present review. If you do not specifically look for a complication, you will not necessarily find it. This is particularly the case for those complications like visual field defects, which may not be consciously recognized by the patient, but may still be functionally limiting. For example, according to table 3, only 8/334 patients had post-operative visual field defects, which are usually detected only by systematic formal visual field testing. It is likely that a much larger number of patients had visual field defects than reported in the reviewed studies. Indeed, not all the 27 studies selected by the authors’ very strict criteria systematically and prospectively looked for all complications.
Because a “Views and Reviews” published in Neurology has a large impact and is typically considered the quintessential reference on the topic; we would like to emphasize the difficulty of evaluating the frequency of neurologic complications without properly designed prospective studies. The percentages provided by this review probably do not reflect the true morbidity and mortality following pallidotomy in PD.
References:
1) De Bie RMA, de Haan RJ, Schuurman PR, Esselink RAJ, Bosh DA, Speelman JD. Morbidity and mortality following pallidotomy in Parkinson’s disease. A systematic review. Neurology 2002;58:1008-1012.
2) Biousse V, Newman NJ, Carroll C, et al. Visual fields in patients with posterior GPi pallidotomy. Neurology 1998;50:258-265.