Where Neuromuscular Disease Meets Cardiac Dysfunction

Cardiovascular Report
January 7, 2015

Because the conduction system disease in myotonic muscular dystrophy tends to progress faster and more unpredictably than in other rhythm disorders, says Saman Nazarian, vigilant monitoring is key.

Eight years ago, Amy Deel, then in her early 30s, noticed that she had difficulty letting go of door knobs and that she would wake up at night with her hands curled up in fists. Deel dismissed both as a nuisance. When she started slurring her speech, Deel was puzzled, but when a laryngeal spasm left her breathless, she got genuinely scared.

Following referral for a neurologic work-up, Deel was told she may have myotonic muscular dystrophy (MMD), a genetic ion-channel disorder occurring at the intersection between neuromuscular and cardiac disease, and should seek specialized care. Deel found it at Johns Hopkins, which has one of the country’s few clinics with a dual-track approach so critical for the follow-up and treatment of a disorder whose neurologic and cardiac pathologies are inextricably intertwined.

Marked by progressive muscle weakness, heart rhythm anomalies and, in 3 to 4 percent of patients, heart muscle dysfunction, MMD commonly presents with subtle, confusing symptoms. Family history, if present, could be a clue, but in Deel’s case there was none, underscoring the medical truism that absence of evidence is not always evidence of absence. 

Deel’s diagnostic trajectory illustrates the wily nature of the disease, says Johns Hopkins cardiology director Gordon Tomaselli who, along with cardiac electrophysiologist Saman Nazarian and neurology colleagues, sees some 150 patients with MMD and as many family members.

Timely diagnosis is critical because the disease can be treated successfully, minimizing—even eliminating—the small but real risk of sudden cardiac death. “With proper follow-up and intervention, the majority of people can live long, healthy lives,” Tomaselli says. 

Any patient who complains of muscle weakness or recurrent muscle contractions should have an ECG, followed by in-depth cardiac and neurologic evaluations. “At the very minimum,” says Tomaselli, “myotonic dystrophy should be in our differential.”

Progressive heart block, severe bradycardia or asystole are the cardiac hallmarks of MMD. Newly diagnosed patients should have a standard ECG complemented by a 24-48 hour Holter monitor, and suspicious or inconclusive ECG findings demand closer follow-up with an ECG at least once a year. A cardiac MRI to rule out myocardial scarring is warranted in those with a history of heart rhythm anomalies, and an electrophysiology study should be considered in those with MRI-confirmed scarring. Patients with worsening conduction disease are good candidates for pacemaker implantation, Nazarian says. The handful who go on to develop left ventricular dysfunction and myocardial scarring—known triggers of dangerous ventricular arrhythmias—should be evaluated for ICD therapy, he adds.

“This is truly a spectrum disease, so individualized risk assessment is critical to avoid over-treatment of those at minimal risk for serious complications,” Nazarian says. To that end, he and Tomaselli have launched studies to help inform risk stratification and to guide therapy. 


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