A 52-year-old woman went to the doctor with complaints of fatigue and shortness of breath during the last year with intermittent dry cough. The patient notes that the latter at times it became difficult for her to raise both hands and comb her hair. During the physical examination found: body temperature - 37.4°C, pulse - 76/min., blood pressure - 130/85 mm Hg st., SpO2 - 95%. During the neurological examination revealed: insignificant decrease in the strength of the deltoid muscle. During lung auscultation revealed: common dry rales. It is observed on the cheeks, around the eyes and on the elbowserythematous rash. Which method is most likely to confirm the diagnosis in this patient?