Features of depression development in myasthenia gravis

The relative risk of developing depression in myasthenia gravis is 2.14 times higher than in the general population. The features of depression in myasthenia patients remain poorly understood and need to be clarified. The purpose of this work was to study the features of the development of depression in patients with myasthenia gravis. From 2014 to 2017, 182 patients with myasthenia gravis were examined. 147 (80.8%) patients had a generalized form of the disease, 35 (19.2%) had an ocular form. The clinical examination included assessment of complaints, medical history, neurological examination, as well as MGFA (Myasthenia Gravis Foundation of America) disease class and subclass of the disease determination. The severity of myasthenia gravis has been quantified according to the QMG score (Quantitative Myasthenia Gravis Score). All the patients were examined for the titer of antibodies to acetylcholine receptors (AchR) and muscle-specific tyrosine kinase (MuSK) by enzyme-linked immunosorbent assay (ELISA). Patients were also tested for the presence of antibodies to titin and SOX1 by indirect immunofluorescence. To detect depression the Beck depression inventory (BDI) was used. The mean depression score in the total sample was 16.0 (10.0; 24.0), which corresponds to a moderate depression level. The mean depression score in patients with ocular form was 6.0 (3.0; 11.0) points (ie, depression is absent), whereas in patients with generalized myasthenia gravis – 19.0 (12.0; 29.0) points (corresponds to moderate depression) (p <0.001). The distribution of patients with mild depression was also uneven: significantly bigger part of the patients was recorded with myasthenia gravis of class I (ocular form) – 10 (28.6%), and with myasthenia gravis of class II – 23 (44.2%). Among the patients with myasthenia gravis of class III, only 13 (20.3%) patients were reported with mild depression and 1 (3.2%) with class IV, p<0.001. The distribution of patients with moderate depression was the opposite of others: most patients had myasthenia gravis of class II – 12 (18.8%), and there were no patients with myasthenia gravis of class I. A similar tendency is also observed in the case of severe depression: patients with myasthenia gravis of class II – 23 (35.6%) dominated, to a lesser extent - patients with myasthenia gravis of class IV – 6 (19.4%). Among patients with ocular myasthenia gravis, only 1 (2.9%) patient was found to have severe depression. Severe depression was mainly recorded in patients with myasthenia gravis of class IV – 22 (71%) patients. The number of patients with severe depression has been decreased in the class of myasthenia gravis: 13 patients (20.3%) patients with ІІІ class, 1 (1.9%) with II class, no patients with class I. The degree of depression correlates with the clinical form of myasthenia gravis (ρ= -0.52; p<0.001), class (ρ= -0.30; p<0.001) and the subclass of the disease according to MGFA (ρ= -0.36; p<0.001). A reliable correlation relationship was established between the quantitative evaluation of the severity of myasthenia gravis (according to the QMG score) and the results of the evaluation according to the BDI score in the total sample (ρ=0.73; p<0.001). The assessment indicators on the QMG score and the BDI score significantly correlated in patients with ocular (ρ=0.36; p<0.05) and generalized forms (ρ=0.67; p<0.05). In addition, the level of depression correlates with the presence (ρ=0.15; p=0.040) and the titer of antibodies to AchR (ρ=0.42; p<0.001), with the presence (ρ=0.18; p=0.016) and the titer of antibodies to MuSK-AB (ρ=0.19; p=0.011). No correlation was found between the presence of antibodies to titin and to SOX1 (ρ=0.14; p<0.05 and ρ=0.07; p