The MoCA: Well-suited screen for cognitive impairment in Parkinson disease
JohanMarinus, Senior Researcher, Leiden University Medical Centerj.marinus@lumc.nl
Dagmar Verbaan, Jacobus J. van Hilten
Submitted February 02, 2011
We read the article by Dalrymple-Alford et al. who compared the diagnostic accuracy of the MoCa with the S-MMSE and the SCOPA-COG in healthy controls, PD patients without dementia (PD-N), PD patients with mild cognitive impairment (PD-MCI), and PD patients with dementia (PD-D). [1]
As developers of the SCOPA-COG, [2] we were interested in the comparison between the SCOPA-COG and the MoCa. The authors concluded that "all 3 mental status tests produced excellent discrimination of PD-D from patients without dementia, and PD-MCI from PD- N patients but [that] the MoCA was generally better suited across both assessments." The S-MMSE and MoCa were administered to all patients allowing head-to-head comparisons between both scales. In addition, it permitted the transformation of the data to other prevalence rates (see footnote c in Table 3).
However, the SCOPA-COG was not administered in 38 out of the 114 PD patients (37 PD-N and 1 PD-D). We were surprised that the diagnostic accuracy between the MoCa and SCOPA-COG was directly compared. A direct comparison of these parameters is only justified if the populations are identical; the comparison should therefore have been restricted to subjects in whom both instruments were administered.
Even at a constant specificity, a higher number of non-cases within the sample -as in the case of the MoCa- would affect the NPV and PPV. At higher specificity values, as in the current situation, this would have led to an increase of the NPV and a decrease of the PPV. The effect of these errors is likely to pertain to the comparison between PD-MCI and PD-N patients in particular, since here the SCOPA-COG was administered in less than half the number of PD-N patients compared to the MoCa. We ignored that a different specificity value could have been obtained for the SCOPA-COG, had all PD patients been assessed with this scale. This is very possible and would make the data even less comparable.
The authors can not draw valid conclusions regarding the difference in diagnostic accuracy between the MoCa and SCOPA -COG on the basis of the presented data. We encourage them to re-analyze the data while restricting the analysis to the population in whom both the MoCa and the SCOPA-COG was administered.
References
1. Dalrymple-Alford JC, MacAskill MR, Nakas CT, et al. The MoCA. Neurology 2010 Nov 9;75:1717-1725.
2. Marinus J, Visser M, Verwey NA, et al. Assessment of cognition in Parkinson's disease. Neurology 2003;61:1222-1228.
Disclosure: Dr. van Hilten served on the scientific advisory board and as a consultant for Novartis and GSK; received funding from the Netherlands Ministry of Economic Affairs (TREND [Trauma RElated Neuronal Dysfunction]; and is an editorial board member of Movement Disorders. Drs. Marinus and Verbaan report no disclosures.
We read the article by Dalrymple-Alford et al. who compared the diagnostic accuracy of the MoCa with the S-MMSE and the SCOPA-COG in healthy controls, PD patients without dementia (PD-N), PD patients with mild cognitive impairment (PD-MCI), and PD patients with dementia (PD-D). [1]
As developers of the SCOPA-COG, [2] we were interested in the comparison between the SCOPA-COG and the MoCa. The authors concluded that "all 3 mental status tests produced excellent discrimination of PD-D from patients without dementia, and PD-MCI from PD- N patients but [that] the MoCA was generally better suited across both assessments." The S-MMSE and MoCa were administered to all patients allowing head-to-head comparisons between both scales. In addition, it permitted the transformation of the data to other prevalence rates (see footnote c in Table 3).
However, the SCOPA-COG was not administered in 38 out of the 114 PD patients (37 PD-N and 1 PD-D). We were surprised that the diagnostic accuracy between the MoCa and SCOPA-COG was directly compared. A direct comparison of these parameters is only justified if the populations are identical; the comparison should therefore have been restricted to subjects in whom both instruments were administered.
Even at a constant specificity, a higher number of non-cases within the sample -as in the case of the MoCa- would affect the NPV and PPV. At higher specificity values, as in the current situation, this would have led to an increase of the NPV and a decrease of the PPV. The effect of these errors is likely to pertain to the comparison between PD-MCI and PD-N patients in particular, since here the SCOPA-COG was administered in less than half the number of PD-N patients compared to the MoCa. We ignored that a different specificity value could have been obtained for the SCOPA-COG, had all PD patients been assessed with this scale. This is very possible and would make the data even less comparable.
The authors can not draw valid conclusions regarding the difference in diagnostic accuracy between the MoCa and SCOPA -COG on the basis of the presented data. We encourage them to re-analyze the data while restricting the analysis to the population in whom both the MoCa and the SCOPA-COG was administered.
References
1. Dalrymple-Alford JC, MacAskill MR, Nakas CT, et al. The MoCA. Neurology 2010 Nov 9;75:1717-1725.
2. Marinus J, Visser M, Verwey NA, et al. Assessment of cognition in Parkinson's disease. Neurology 2003;61:1222-1228.
Disclosure: Dr. van Hilten served on the scientific advisory board and as a consultant for Novartis and GSK; received funding from the Netherlands Ministry of Economic Affairs (TREND [Trauma RElated Neuronal Dysfunction]; and is an editorial board member of Movement Disorders. Drs. Marinus and Verbaan report no disclosures.