The conundrum called cardiomyopathy ! How is DCM different from RCM ,NDCM and MDCM ?
Posted Dec 12 2010 1:26pm
Dilated cardiomyopathy (DCM ) is the commonest cardiac muscle disease .Diagnosis is simple and straight forward. All that we require is, documentation of LV dilatation and contractile dysfunction.The nomenclature of cardiomyopathy has remained a difficult exercise .This is primarily due to iatrogenic & intellectual confusion among cardiologists . They mixed up etiological and morphological entities together , later on they wanted to de-link etiology from morphology , ultimately they realised when illness strikes the heart , it can not differentiate the morphology, etiology and pathology as we would want to . So , whenever possible we have to label cardiomyopathy with all components (Dilated cardiomyopathy due to alcohol with some restrictive features.)
This article tries to evoke some thoughts about why LV dilatation is central to the understanding of cardiomyopathy.
DCM is the prototype where LV dilates with global hypokinesia.The upper limit of LV diameter is generally considered to be 56mm in diastole. (Range 35 -56mm) .This cut off point is too empirical for the simple reason, the left ventricle can dilate up to 50 % from it’s basal diameter and still technically be within normal limits.( A 3.5 cm LV ( end diastolic diameter ) can dilate to 5.6 cm ,i e a 50 % dilatation , still LV has not reached the upper limit of normal )
Even as we do not have a clear answer to the above issue , we recognise left ventricle muscle can hypertrophy, progressively dilate , transiently dilate, fail to dilate , regressively dilate or hypotrophy .These changes can be dynamic and heavily influenced by hemodynamic and local pathologic factors like fibrois, interstitial proliferation etc. Meanwhile , the pharmacological , surgical /catheter injuries we inflict , modifies the muscle behavior in a positive or negative manner.
In this back ground , we have found a new entity called NDCM .
Apart from DCM, a newer form of cardiomyopathy is being recognized .This is often referred to as NDCM (Non dilated cardiomyopathy) .Global systolic LV dysfunction with normal LV dimension.This a similar to the terminology MDCM (Minimally/Mildly dilated cardiomyopathy where LV dimension do not increase beyond 15 % upper limit of normal ) .
This is seen in CKD and diabetic individuals.Atria may be enlarged .Diastolic dysfunction may co exist. It is no surprise, this entity closely mimics RCM. But in RCM LV systolic function is not greatly compromised till the late stages , while NDCM it begins with systolic dysfunction. This is the only difference .There can be overlaps .
MDCM was reported in 1990 . Keren gave a excellent insight about the condition , It is unfortunate it failed to take off as a popular clinical entity . Cardiologists are argued to use this term liberally in their clinical practice .
Cardiology is not that simple as one would like to ! The two components of cardiomyopathy ie LV dilatation and LV dysfunction can be temporally dissociated one may precede the other. To complicate the matter further, one of them may not manifest at all !
Few , still consider many of the RCMs and NDCM are one and the same entities that present in different time frames in their natural history.
So the simplified concept to decode the cardiomyopathy conundrum could be
When both dilatation and dysfunction occur it is classical DCM
When dysfunction alone occur without dilatation it is NDCM
When both dysfunction and dilatation are less it is RCM*(Relaxyl dysfunction must)
When dilatation is mild and dysfunction is severe it is MDCM