Sick sinus syndrome concomitant with myopathy associated with anti-mitochondrial antibodies: a case report

BACKGROUND: Anti-mitochondrial antibody (AMA)-associated myopathy is known to be concomitant with primary biliary cirrhosis and to cause both skeletal muscle disorders and arrhythmias, myocardium disorders, and respiratory muscle disorders. We report a case of AMA-associated myopathy in which the bradycardia-related symptoms preceded the skeletal muscle symptoms. CASE SUMMARY: A 59-year-old woman visited the emergency room in our hospital following a syncopal event. The patient was bradycardiac (45 b.p.m.) with a junctional rhythm resulting from sick sinus syndrome (SSS) and was suffering from heart failure. Blood tests revealed elevated creatine kinase (CK) and hepatic enzymes. She underwent permanent pacemaker implantation. However, it proved difficult to detect the electrical potential in the right atrium. Although successful atrial pacing was achieved at the lower right atrial septum, the atrial threshold was markedly high and she depended on ventricular pacing. One year later, neurological examination and muscle biopsy confirmed the diagnosis of AMA-associated myopathy. Following this diagnosis, steroid pulse therapy was initiated. Steroid administration relieved her symptoms and lowered the CK levels but the atrial standstill persisted. The patient takes low-dose prednisolone and has had an uneventful course for 3 years. DISCUSSION: To the best of our knowledge, this is the first case of AMA-associated myopathy diagnosed by the first symptom related to bradycardia due to SSS. Patients with AMA-associated myopathy can experience a variety of cardiac symptoms, including arrhythmias, and initially complain of cardiac symptoms without symptoms of skeletal myopathy. This disease should be considered when diagnosing patients with arrhythmia and elevated CK.