PEDIATRIC CARDIOMYOPATHY DEFINED
With the pediatric population, cardiomyopathy occurs in approximately 12 children out of every million with about 1,000-5,000 new cases diagnosed each year. The majority of diagnosed children are infants under the age of 12 months with fewer cases between the ages of 1 to 12 years. When cardiomyopathy is diagnosed in children before puberty, it is considered extremely unusual and it may not have the same causes, manifestations or disease progression as cardiomyopathy in adults.
There is a vast amount of literature on adult cardiomyopathy but not all of the information is relevant to children diagnosed with the disease. Unfortunately, there has been little research and focus on pediatric cardiomyopathy over the years. Consequently, the causes are not well understood. According to the Pediatric Cardiomyopathy Registry, less than 25% of all patients have an identified cause despite rigorous, standardized evaluation. What is known is that the underlying causes of cardiomyopathy in infants and children may be considerably different from that diagnosed in adolescents and adults with similar symptoms. Pediatric cardiomyopathy is more likely to be due to genetic factors while lifestyle or environmental factors play a greater role in adult cardiomyopathy.
In rare cases, pediatric cardiomyopathy may be a symptom of a larger genetic disorder that may not be immediately detected. For example, when an infant or young child is diagnosed with dilated cardiomyopathy, a rare genetic heart disease called Barth Syndrome or a mitochondrial defect (i.e. Kearns-Sayre syndrome) may be the cause. Similarly, a child with severe hypertrophic cardiomyopathy may actually have Noonan Syndrome, Pompe disease (type II glycogen storage disease), a fatty acid oxidation disorder, or mitochondrial HCM. It is therefore important for any diagnosed child to be properly evaluated for other suspected genetic disorders. A thorough evaluation remains a complicated and expensive process due to the large number of rare genetic causes, the broad range of symptoms and the existence of many specialized biochemical, enzymatic and genetic tests. Verifying a diagnosis may require getting additional blood, urine or tissue tests and consulting other specialists such as a neurologist and geneticist.
Cardiomyopathy in children may also present differently from diagnosed teenagers or adult. It is considered unusual when an infant or a child is diagnosed with symptoms at such a young age. Typically, symptoms are not apparent until the late teens or adult years when most patients are diagnosed. With hypertrophic cardiomyopathy, the disease commonly develops in association with growth and is detected when a child progresses through puberty. Even in genetically affected family members, a child that carries the muted gene from birth may appear to have a normal heart and be asymptomatic until puberty.
A diagnosis at a young age usually, but not always, signifies a serious heart condition that requires aggressive treatment. The concern lies in the uncertainty of how the heart muscle will respond with each additional growth spurt. With some older children, the condition may stabilize over time with the aid of certain medications or surgery. In severe cases, small children may experience progressive symptoms quickly leading to heart failure. This presentation contrasts with most diagnosed adults who may only have minor symptoms without serious limitations or major problems for years.
Aside from differences in the cause and manifestation, cardiomyopathy may also progress differently in children than adults. When children are diagnosed at an early age, the prognosis may be poor depending on the form of cardiomyopathy and the stage of the disease. For example, dilated cardiomyopathy can progress quite rapidly when diagnosed in young children. Up to 40% of diagnosed children with dilated cardiomyopathy fail medical management within the first year of diagnosis and of those that survive many have permanently impaired heart function. Children diagnosed with hypertrophic cardiomyopathy seem to fare better but the outcome is highly variable.
Mortality and heart transplant rates of childhood cardiomyopathies are much higher than in adults due to the rarity and uncertainty of the disease. Less than optimal outcomes may be attributed to the more fragile state of infants and young children or it may be a function of the disease's advanced progression associated with another genetic disorder. Another unfortunate reason is that cardiomyopathy is not usually detected until the end stage when obvious symptoms of heart failure are apparent. Cardiomyopathy can be easily missed in routine check-ups when there are no obvious symptoms (i.e heart murmur) or when there is no reason for diagnostic testing (i.e. no family history of the disease).