Asymptomatic, Nonsustained Ventricular Tachycardia in Myotonic Dystrophy Type 1 Detected with a Loop Recorder

predominance (M3+ to M4+), weakness for hip flexion bilaterally (M5–), and for foot extension and flexion bilaterally (M2 and M4–), hyperextensible joints, absent tendon reflexes, hypotonia, ataxia, and a positive Gower’s sign. Creatine kinase was 60 U/l (normal: ! 171 U/l). Hb A 1c was 6.4% (normal: 3.5–6.0%). Triglycerides and cholesterol were elevated. Ophthalmologic investigations revealed mild cataract and a CT scan of the brain showed moderate widening of the ventricles and a considerable falx meningioma. Nerve conduction studies disclosed polyneuropathy. Needle electromyography showed typical abnormal spontaneous activity and a myogenic motor unit architecture. Analysis for mutations in the DMPK gene on chromosome 19q13.3 revealed a CTG-repeat expansion of 1,333 repeats in nuclear DNA from blood lymphocytes. The mutation was also found in his brother (1,333 repeats). His mother was clinically affected as well, had developed left bundle-branch block, and had died at age 55 years from sudden cardiac death. His medical history was negative for arterial hypertension, diabetes, angina pectoris, coronary heart disease, dyspnea, leg edema, syncope, or palpitations. The patient was first investigated for cardiac involvement at age 31 years, revealing normal P-Q interval (0.18 ms) and ST elevation on ECG and slight tricuspid insufficiency on echocardiography. At age 36 Cardiac involvement is a dominant feature of myotonic dystrophy type 1 (MD1) [1] . Cardiac involvement in MD1 manifests as impulse generation or impulse conduction disturbances or cardiomyopathy [1] . Since cardiac involvement predicts the outcome of these patients [2, 3] , it is important to detect cardiac involvement as soon as possible after establishing the neurological diagnosis to initiate adequate cardiac therapy. Though ventricular tachyarrhythmias (VTs) are a frequent finding in MD1 patients [3–6] , they are usually detected only after patients have become symptomatic. Asymptomatic, nonsustained VT is usually detected only by 24-hour ambulatory ECG or loop recording as in the following case.