Diagnosis of myasthenia gravis in a patient with polymyositis

In recent years, there has been an increase in publications on rare cases of combined myasthenia gravis and idiopathic inflammatory myopathies, including polymyositis. Such cases complicate the differential diagnosis and worsen patients' prognosis. This article presents a rare case of a patient with two serious autoimmune diseases: myasthenia gravis and polymyositis. A clinical case of the ocular form of myasthenia gravis in a 60-year-old woman with a long history of polymyositis is presented, with a detailed discussion of diagnostic and treatment stages. Clinically, polymyositis was manifested by proximal tetraparesis and confirmed by electromyography and biopsy data, and a good response to glucocorticoid therapy. Decrement test results were within acceptable limits. An increase in creatine phosphokinase up to 1630 U/L was observed. Ocular myasthenia gravis was diagnosed based on clinical criteria, with a positive pharmacological fatigue test (positive proserin test). Literature reviews on this topic are presented, emphasizing the importance of early diagnosis and adequate pathogenetic therapy to improve the prognosis for both polymyositis and myasthenia gravis.