BACKGROUND. There are many studies in the literature suggesting that cognitive impairment is more pronounced in patients with myasthenia gravis compared with healthy people, but there is no explanation of the reasons and mechanisms. However, the reverse character the influence of intellectual-mnestic disorders on the course of myasthenia gravis has not been studied enough. AIM. To compare clinical, anamnestiс, laboratory and instrumental data in patients with myasthenia gravis according to the presence or absence of cognitive impairment. MATERIAL AND METHODS. 61 patients with a confirmed diagnosis of myasthenia gravis were divided into 2 groups according to the Montreal cognitive test. Patients scoring 25 or less were assigned to the first group, those scoring 26 points or more to the second group. A comparative assessment was made according to the myasthenia gravis impairment index, age of onset, duration of the disease, duration of hospitalization, severity of myasthenia gravis according to clinical scales, body mass index, electroneuromyography data, levels of antibodies to the acetylcholine receptor and skeletal muscles, and daily doses of the drugs received. RESULTS. In the 1st group, there was a significantly higher score on the Generalised Disorders subscale of the Myasthenia Gravis Impairment Index; the severity of Quantitative myasthenia gravis score was significantly higher in the 1st group than in the 2nd both for the total score and for the Musculoskeletal Lesions subscale. On average, 49 mg more pyridostigmine bromide was required in the first group, while the average body mass index was significantly lower in the first group. CONCLUSION. The presence of a cognitive deficit in patients with myasthenia gravis may worsen the clinical picture of the disease, which should be taken into account by clinicians, especially in elderly patients, who are at increased risk of developing cognitive disorders.

Myasthenia gravis is a rare autoimmune disease, the clinical picture of myasthenia gravis is manifested by fluctuating weakness, pathological muscle fatigue and it is difficult for clinicians to diagnose it appropriately. The article presents a clinical case of misdiagnosis of late-onset myasthenia gravis, it provides a chronology of the development of symptoms of the disease and an analysis of the difficulties of differential diagnosis. Despite the typical manifestations of myasthenia gravis, the patient did not receive propriate pathogenetic therapy for a long time, while he was prescribed drugs that block neuromuscular conduction and worsen the course of the disease.