RBB

[Jo80]

My son which is five was diagnosed with a myopathy but don't know for sure what kind it actually is. The neurologist said he was leaning more toward a begign congential myopathy. He has been a floppy baby ever since he was born and that is one of the signs of it. However, when we went to him and him about the heart muscle he said he would send us to a cardiologist. We went to the cardiologist and he did an EKG and a Echo. The Echo came back normal however that wasn't the case for the EKG. The EKG showed up Incomplete right bundle block. Now I am scared to death he is going to get cardiomyopathy. Can anyone help me with this? Does anybody know anything about it?

[Jeffrey R Boris, M.D.]

Dear Jo,

A myopathy is abnormal muscle.  In your son’s case, it is being used to describe the skeletal muscle abnormality.  They are typically due to a genetic error that codes for a protein or some other structural component of the muscle, for a component inside of cells, or for a component of the connective tissue.  However, a cardiomyopathy is one in which specifically the heart muscle is abnormal.  There are all kinds of myopathies, some of which affect the heart and others that don’t.  As well, there are different kinds of cardiomyopathies.  At this point, without being able to evaluate your son’s information, I can’t say whether this myopathy includes the heart or not.  I do have to say that just because your son’s echocardiogram is normal now does not necessarily mean that it won’t be later UNLESS you get an exact diagnosis.  I would consider having him seen by a genetics and metabolism specialist, as a clinical diagnosis may not be adequate without things like laboratory blood studies, genetic studies, and even, possibly, a muscle biopsy.  A more definitive diagnosis can then be used to say whether his myopathy is associated with cardiomyopathy, or not.

That said, I do have good news:  incomplete right bundle branch block (iRBBB) is a normal variant which we see frequently in children.  For our other readers, iRBBB is a finding diagnosed on the ECG.  It demonstrates a very mild delay in the electrical conduction system from the AV node in the center of the heart down to the right ventricle, the pumping chamber on the right.  It typically does not cause any heart problems and does not progress.  I can’t say for sure whether your son’s is benign, but there is a good chance that it is, and that it has nothing to do with his myopathy.