PPollak, Joseph Fourier University Grenoble Franceppollak@ujf-grenoble.fr
P D Charles, N Van Blercom, P Krack, S L Lee, J Xie, G Besson, and A L Benabid
Submitted October 29, 2002
We thank Dr Montgomery for his comments and share his concern about
the importance of adequately selecting parkinsonian patients for surgery.
Dr Montgomery's remark deals with the use of regression and correlational
analyses to study the predictive factors of outcome from bilateral
subthalamic nucleus stimulation. While it is true that the regression
analysis of the data is retrospective, the original patient enrollment,
treatment, and data collection was performed prospectively. The
calculation of the sensitivity, specificity, and confidence intervals
would need considerably more patients, hardly compatible with this type of
therapeutic procedure. The receiver-operating-characteristic curves
proposed by Dr Montgomery are frequently used to assess the usefulness of
diagnostic markers, but the method also has some disadvantages. [1] We
think that univariate analysis is one of the most appropriate statistical
methods for our study. We agree with the necessity of validating our
model in another prospective study. We do not know if “the large majority
of times, the specificity and sensitivity of protectors fall when tested
prospectively” but it has been shown that it is not always true. [2]
Most studies of the surgical treatment of PD found that outcome from
surgery are better in patients with levodopa-responsive motor symptoms.
Welter et al. [3] also used regression analysis in their series of
parkinsonian patients treated with subthalamic nucleus stimulation. In
keeping with our results they found that the outcome of STN stimulation
was excellent in levodopa-responsive forms of PD. Our results are
consistent with the classical inclusion criteria for subthalamic nucleus
stimulation and imply that the decision to operate on the oldest patients
and/or patients with levodopa resistant motor symptoms should be
carefully weighed. The other lesson from our experience is that
parkinsonian patients with severe levodopa-induced motor complications may
still be surgical candidates if a fair levodopa response is maintained,
i.e. if their best on-motor score is low. This result is clinically
sensible. The relative young age at the time of surgery could have been
expected as a good predictor since young-onset PD is characterized by a
good response to levodopa with minimal on-period axial or non-motor
symptoms except fluctuations and dyskinesias. [4] Moreover, surgery
related complications are more frequent in an elderly population.
References
1. Feinstein AR. Clinical epidemiology. The architecture of clinical
research. Philadelphia: WB Saunders Company, 1985.
2. Besson G, Robert C, Hommel M, Perret J. Is it clinically possible
to distinguish non-hemorrhagic infarct from hemorrhagic stroke? Stroke
1995;26:1205-1209.
3. Welter ML, Houeto JL, Tezenas du Montcel S, Mesnage V, Bonnet
AM,Pillon B, Arnulf I, Pidoux B, Dormont D, Cornu P, Agid Y. Clinical
predictive factors of subthalamic stimulation in Parkinson's disease.Brain
2002;125:575-583.
4. Quinn N, Critchley P, Marsden CD. Young onset Parkinson's disease.
Mov Disord 1987;2:73-91.
We thank Dr Montgomery for his comments and share his concern about the importance of adequately selecting parkinsonian patients for surgery. Dr Montgomery's remark deals with the use of regression and correlational analyses to study the predictive factors of outcome from bilateral subthalamic nucleus stimulation. While it is true that the regression analysis of the data is retrospective, the original patient enrollment, treatment, and data collection was performed prospectively. The calculation of the sensitivity, specificity, and confidence intervals would need considerably more patients, hardly compatible with this type of therapeutic procedure. The receiver-operating-characteristic curves proposed by Dr Montgomery are frequently used to assess the usefulness of diagnostic markers, but the method also has some disadvantages. [1] We think that univariate analysis is one of the most appropriate statistical methods for our study. We agree with the necessity of validating our model in another prospective study. We do not know if “the large majority of times, the specificity and sensitivity of protectors fall when tested prospectively” but it has been shown that it is not always true. [2]
Most studies of the surgical treatment of PD found that outcome from surgery are better in patients with levodopa-responsive motor symptoms. Welter et al. [3] also used regression analysis in their series of parkinsonian patients treated with subthalamic nucleus stimulation. In keeping with our results they found that the outcome of STN stimulation was excellent in levodopa-responsive forms of PD. Our results are consistent with the classical inclusion criteria for subthalamic nucleus stimulation and imply that the decision to operate on the oldest patients and/or patients with levodopa resistant motor symptoms should be carefully weighed. The other lesson from our experience is that parkinsonian patients with severe levodopa-induced motor complications may still be surgical candidates if a fair levodopa response is maintained, i.e. if their best on-motor score is low. This result is clinically sensible. The relative young age at the time of surgery could have been expected as a good predictor since young-onset PD is characterized by a good response to levodopa with minimal on-period axial or non-motor symptoms except fluctuations and dyskinesias. [4] Moreover, surgery related complications are more frequent in an elderly population.
References
1. Feinstein AR. Clinical epidemiology. The architecture of clinical research. Philadelphia: WB Saunders Company, 1985.
2. Besson G, Robert C, Hommel M, Perret J. Is it clinically possible to distinguish non-hemorrhagic infarct from hemorrhagic stroke? Stroke 1995;26:1205-1209.
3. Welter ML, Houeto JL, Tezenas du Montcel S, Mesnage V, Bonnet AM,Pillon B, Arnulf I, Pidoux B, Dormont D, Cornu P, Agid Y. Clinical predictive factors of subthalamic stimulation in Parkinson's disease.Brain 2002;125:575-583.
4. Quinn N, Critchley P, Marsden CD. Young onset Parkinson's disease. Mov Disord 1987;2:73-91.