Case Presentation: A 47-year-old male presented with distal extremity and facial weakness. Physical exam and electroencephalogram showed myopathy with myotonic features and a distal predominance, characteristic of myotonic dystrophy type 1. Patient denied any chest pain, shortness of breath, presyncope, syncope, and palpitations. Due to associated risk of cardiac-related complications, a baseline electrocardiogram (ECG) was obtained, which showed sinus rhythm with marked sinus arrhythmia, left axis deviation, heart rate of 66 bpm, PR interval 180 ms, QRS interval 92ms and QTc interval 406ms. Echocardiogram showed concentric left ventricular hypertrophy and an ejection fraction of 60-64%.An ambulatory outpatient ECG monitoring via Holter for 48 hours was obtained to monitor for clinically asymptomatic arrhythmias and showed a predominant sinus rhythm of 46 to 170 bpm and a mean rate of 92 bpm, periods of observed bradycardia predominantly occurring during nocturnal hours, rare multiform premature ventricular complexes with few ventricular trigeminy, a rare atrial ectopy with a 6 beats run of supraventricular tachycardia at a rate of 170 bpm, normal diurnal variation in heart rates, and normal heart rate variability. No significant ST segment deviations were observed and no pauses were noted. Given the supraventricular tachycardia, the patient was referred to cardiac electrophysiology for further evaluation and possibly more extended cardiac monitoring with an event monitor/implantable loop recorder.
Discussion: The classic symptom of myotonia is not always the first presenting feature nor does it always present. Leg weakness, unexplained extremity pain, and fatigue may be the first signs of disease activity. Notably, cardiac manifestations may present prior to any musculoskeletal symptomatology. Cardiac arrhythmias in an otherwise young, healthy individual may be the presenting sign of DM, and a thorough work up for DM should be pursued. DM is shown to cause cardiac dysfunction via alteration in troponin T, affecting cardiac contractility, abnormal splicing of SCN5A, leading to conduction system disease with prolonged PR and QRS durations, and upregulation of CELF1, which causes arrhythmias and structural heart defects. The patient presented in this case report exhibits features of myotonic dystrophy type I with left axis deviation, concentric left ventricular hypertrophy, periods of bradycardia, multiform premature ventricular complexes, and atrial ectopy runs of supraventricular tachycardia. Clinical detection of DM requires a thorough review of patient symptomatology.
Conclusions: For patients known to have DM, regular cardiac screening is imperative. Even in patients not experiencing cardiac symptoms such as presyncope or palpitations, annual EKGs and echocardiography are needed. Abnormal EKG findings are seen in over half of DM patients, and structural disease may begin to manifest well before cardiac symptoms begin. Atrial and ventricular arrhythmias occur, and electrophysiology studies are of use for both, as it has a positive predictive value for sudden cardiac death. Tissue doppler imaging may aid in early detection of cardiac disease and allows for evaluation of patients’ ejection fraction. Patients with severe arrhythmias or a high positive predictive value of sudden cardiac death necessitate interventional steps. Cardiac manifestations of DM are the second-leading cause of mortality for patients with DM, and regular cardiac screening is essential.