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Journal of cardiac diseases and advanced treatment (JCDAT)

Editorial

X-linked dilated cardiomyopathy or Becker muscle dystrophy with dominant cardiac involvement

*Corresponding author: Josef Finsterer*, MD, PhD, Krankenanstalt Rudolfstiftung, Messerli Institute, Veterinary University of Vienna, Vienna, Austria, Europe, E-mail: fifigs1@yahoo.de

Article Information

Article Type: Editorial

Received : 02/11/2018 
Accepted : 15/11/2018
Published : 25/11/2018

Abstract

Key words: mitochondrial disorder, multisystem, mtDNA, phenotype, genotype

Article

Letter to the Editor

In a recent article, Chamberlain et al. reported about a 16yo male with dystrophinopathy due to a duplication of exons 13-16 in the dystrophin gene, diagnosed as X-linked dilated cardiomyopathy (XLDCMP) [1]. We have the following comments and concerns.

Dilated cardiomyopathy (DCMP) is usually not associated with creatine-kinase (CK)-elevation unless the underlying disorder is a muscle disease. CK-elevation in the presented patient most likely originated from the skeletal muscle. CK-elevation may go along with normal clinical exam but subclinical involvement of the muscle may be found on blood tests, electromyography, muscle MRI, ultrasound, or muscle biopsy. It is not conceivable why the patient did not undergo instrumental investigations to look for subclinical muscle involvement. Diagnosing muscle involvement is important since dystrophinopathy patients with muscle involvement may profit from administration of steroids, in particular deflazacort [2]. Secondly, the prognosis might be different if the muscle is additionally involved since the decision for or against heart transplantation (HTX), in case the patient develops intractable heart failure, may be influenced by the presence or absence of muscle affection. Thirdly, patients with dystrophinopathy may develop involvement of the respiratory muscles, lastly requiring ventilatory support. 

Concerning dCMP, it would be helpful to know the degree of myocardial fibrosis, a frequent finding in dystrophic cardiomyopathy. Myocardial fibrosis may be subendocardial, supepicardial, midmyocardial, or transmural. Fibrosis may be patchy or diffuse [3]. Did the patient undergo cardiac MRI and was late gadolinium enhancement (LGE) determined? Myocardial fibrosis may be involved in the pathogenesis of arrhythmias why it is essential to confirm or rule it out.

Sinus tachycardia is a frequent ECG abnormality in dystrophinopathies and most likely represents a compensatory mechanism. Assuming that sinus tachycardia represents a compensatory mechanism, radiofrequency ablation is rather harmful than beneficial. 

DCMP may occur in a number of other NMDs in addition to dystrophinopathies. These include myotonic dystrophies, limb girdle muscular dystrophies, congenital myopathies, myofibrillar myopathies or metabolic myopathies [4]. More rarely DCM occurs in congenital muscular dystrophies, Barth syndrome, oculopharyngodistal myopathy, inclusion body myopathy, polymyositis, or dermatomyositis. Why did the authors choose to test for dystrophinopathy and not for other NMDs?

In conclusion it is strongly recommended that the presented patient undergoes instrumental skeletal muscle examination, since it is quite likely that he needs to be re-classified as BMD with predominant cardiac involvement. Furthermore, the patient requires close follow-up to monitor muscle strength, the ability to ambulate, and putative involvement of the respiratory muscles. Also the mother needs to be examined for subclinical muscle involvement. Dystrophinopathies of whatever genetic cause represent a continuum between two ends. On the one end there is severe muscle involvement but only mild or absent cardiac disease. On the other end there may be severe cardiac disease but only mild muscle manifestations, such as hyper-CKemia. As long as the muscle is not thoroughly investigated in patients with hyper-CKemia, it is not justified to hypothesis that muscle disease is absent. 

 

References

1 Chamberlain RC, Smith EC, Campbell MJ. (2015) Novel Rod Domain Duplication in Dystrophin Resulting in X-Linked Dilated Cardiomyopathy.
   Pediatr Neurol; 53:439-41.
2 Finsterer J, Cripe L. (2014) Treatment of dystrophin cardiomyopathies. Nat Rev Cardiol; 11:168-79.
3 Tandon A, Jefferies JL, Villa CR, Hor KN, Wong BL, et al. (2015) Dystrophin genotype-cardiac phenotype correlations in Duchenne and Becker
   muscular dystrophies using cardiac magnetic resonance imaging. Am J Cardiol; 115:967-71.
4 Finsterer J, Stöllberger C, Wahbi K. (2013) Cardiomyopathy in neurological disorders. Cardiovasc Pathol; 22:389-400.

 

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