Prognosing the severity of the myasthenia gravis
Summary. The aim — to develop a prognostic model of the severe course (SC) of myasthenia gravis (MG) taking into account the clinical manifestations and the immunological type of the disease. Materials and methods. 182 patients with MG were examined (147 (80.8%) with a generalized, 35 (19.2%) with ocular form of the disease). To assess the clinical form, class, and subclass of MG, the MGFA classification was used. The severity of MG was quantified on a QMG scale. The level of antibodies to acetylcholine receptors (AchR-AB) and to muscle-specific tyrosine kinase (MuSK-AB) and the presence of antibodies to titin and SOX1 were assessed. The quality of life was assessed on the MGQОL-15, daily activity — on the MG-ADL, the level of fatigue — on the FSS scale. Results. AchR-AB were found in 124 (68.1%) patients (73.5% with generalized and 45.7% with the ocular form), to MuSK — in 16 (8.8%), to titin — in 53 (29.1%), to SOX1 — in 10 (5.5%) patients. The average MG-ADL score in the total sample was 5.0 (3.0–8.0), the FSS score — 43.0 (30.0–54.0), the MGQOL-15 score — 21.5 (9.0–33.0) points. According to ROC-analysis, it was found that out of all assessed indicators, the titer of AchR-AB has the best operational characteristics (the highest sensitivity and specificity, AUC), its ability to predict the SC of MG is very good (sensitivity 70.59; specificity 90.30; AUC 0.835; p<0.001) and it can be used to predict the SC of MG (>17 points on the QMG scale). If the titer level of AchR-AB is >6.9 nmol/L, the odds ratio of the SC of MG in patients with MG compared to those who have a titer level of AchR-AB below this level is 22.35 (95% confidence interval 6.98–71.56; p<0.001. The SC of MG (>17 points on the QMG scale), according to the rank correlation analysis, is associated with the titer of AchR-AB (ρ=0.34; p<0.001), with the MGQOL-15 score (ρ=0.41; p<0.001), MG-ADL score (ρ=0.41; p<0.001), FSS score (ρ=0.36; p<0.001). Conclusion. An AchR-AB >6.9 nmol/L is a predictor of SC of MG. The prognostic value of the titer of MuSK-AB, of the presence of antibodies to titin, to SOX1 for severe MG has not been established.
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