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Myotonic dystrophy (DM) is a group of inherited neuromuscular disorders with an autosomal dominant pattern of distribution. Even though the overall incidence is low, it remains the most frequently inherited neuromuscular disease of adult life (1). There are two distinct clinical forms, with type 1 (DM1) being more common with a prevalence rate of 1 in 20,000 (2). Type 2 (DM2) has an adult onset with a more favorable clinical course.
DM1 results from an expansion of a repetitive trinucleotide segment in the 3' untranslated region of the myotonic dystrophy protein kinase (DMPK) gene. Based on the age at onset and symptoms, four clinical categories can be distinguished: congenital, childhood, classical (adult-onset), and mild (late-onset) (3).
In general, DM is a multisystem disorder and typically presents as myotonia, muscle weakness, cataract, and cardiac conduction abnormalities (4). Cardiac manifestations are among the most common systemic features of DM and range from simple first-degree atrioventricular (AV) blocks to malignant ventricular arrhythmia. The conduction abnormalities are seen in 65% of patients (5) and typically progress with gradual manifestation over many years; however, the clinical course in an individual patient cannot be predicted.
About 20-30% of DM1 patients die due to cardiac causes (6-8) of which one-third are from a sudden cardiac death. Until recently, sudden death was thought to be primarily the result of conduction blocks. However, recent studies have shown that ventricular tachyarrhythmias are possibly a more frequent cause of death than previously thought (5). Therefore, early electrophysiological (EP) studies are recommended to identify this subgroup and a prophylactic cardiac device (permanent pacemaker and ICD) placement is recommended for those at risk of severe bradycardia or malignant ventricular tachyarrhythmia.
In this case series, we present nine cases of DM in a small, community-based teaching hospital that presented with various cardiac manifestations and received appropriate interventions, to prevent death from sudden cardiac arrest.
Case reports
Case 1
An 82-year-old Caucasian woman with a medical history of hypertension and DM presented with episodes of recurrent lightheadedness, dizziness, and near syncope. The 12-lead EKG showed a rate of 69 beats per minute (bpm), first-degree AV block with a PR interval of 244 milliseconds (ms), and a left axis deviation. There was an intraventricular conduction defect (IVCD) with a left bundle...