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. 2021 Mar 12;12:635419. doi: 10.3389/fneur.2021.635419

Figure 1.

Figure 1

Anti-aquaporin 4 (AQP4)-IgG status does not define distinct subgroups of patients by principle-component analyses (PCA) independent by model, number or type of markers used. Anti-AQP4-IgG status does not define a subgroup (such as anti-AQP4-IgG positive and -negative patients) as demonstrated by the full overlap of the 95% prediction ellipses in principle-component analyses (PCA). This is irrespective of how many and which markers are, or which model is used. Patients with Neuromyelitis optica spectrum disorder (NMOSD) were colored according to their anti-AQP4-IgG-status (A,B) or the second pain variable, describing levels of pain disturbing work during the last 4 weeks (question 22 from the “36-item containing short form health survey,” SF-36 score; in C). Singular value decomposition (SVD) with imputation was used here in all PCAs to calculate principal components (PC). Prediction ellipses are such that with a probability of 0.95, a new observation from the same group will fall inside the ellipse. (A) A PCA was performed with all variables (but not anti-AQP4 statuses) and the patients were marked according to their anti-AQP4-IgG status. The PCA-plot shows PC1 and PC2, explaining 24 and 15% of the total variance, respectively, and was performed using only a limited number of key variables (N = 20) such as the Expanded Disability Status Scale (EDSS), disease activity and severity, sex and age. Prediction ellipses were drawn such that a new observation from the same group will fall inside the ellipse with a probability of 0.95. However, those prediction ellipses as well as the data points completely overlap. No difference based on anti-AQP4-IgG status is visible. (B) As in A, but all 351 variables (symptoms, disabilities, lab values, anamnestic, psychosomatic scores, and clinical markers) which have been recorded for the patients are included in the analysis, except for the anti-AQP4 statuses. Again, no difference based on anti-AQP4-IgG status is visible, in marked contrast to (C): Same as in A but shown are patients having high vs. low levels of interference of pain with normal work (including work outside the home and housework) during the past 4 weeks. A PCA based on the remaining 35 variables from the SF-36 score (except the mentioned pain variable two, for which the patient cases have been colored) is shown. Here, the prediction ellipses for a probability of 0.95, as well as the dots per se, show a remarkable difference between the two groups. AQP4, aquaporin 4; EDSS, Expanded Disability Status Scale; NMOSD, neuromyelitis optica spectrum disorder; PC, principal components; PCA, principle-component analysis; SF-36, 36-item short form health survey; SVD, singular value decomposition.